m_surface.cc

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/*===========================================================================
  === File description
  ===========================================================================*/
 
/*===========================================================================
  === External declarations
  ===========================================================================*/
 
#include <cmath>
#include "array.h"
#include "arts.h"
#include "arts_constants.h"
#include "auto_md.h"
#include "check_input.h"
#include "matpack_complex.h"
#include "fastem.h"
#include "geodetic.h"
#include "interpolation.h"
#include "math_funcs.h"
#include "matpack_math.h"
#include "messages.h"
#include "physics_funcs.h"
#include "ppath.h"
#include "rte.h"
#include "special_interp.h"
#include "surface.h"
#include "tessem.h"
#include "arts_conversions.h"
#include "gas_scattering.h"
 
using Constant::pi;
using Conversion::deg2rad;
 
inline constexpr Numeric EARTH_RADIUS=Constant::earth_radius;
inline constexpr Numeric DEG2RAD = Conversion::deg2rad(1);
 
/*===========================================================================
  === The functions (in alphabetical order)
  ===========================================================================*/
 
/* Workspace method: Doxygen documentation will be auto-generated */
void FastemStandAlone(Matrix& emissivity,
                      Matrix& reflectivity,
                      const Vector& f_grid,
                      const Numeric& surface_skin_t,
                      const Numeric& za,
                      const Numeric& salinity,
                      const Numeric& wind_speed,
                      const Numeric& rel_aa,
                      const Vector& transmittance,
                      const Index& fastem_version,
                      const Verbosity&) {
  const Index nf = f_grid.nelem();
 
  chk_if_in_range("zenith angle", za, 90, 180);
  chk_if_in_range_exclude("surface skin temperature", surface_skin_t, 260, 373);
  chk_if_in_range_exclude_high("salinity", salinity, 0, 1);
  chk_if_in_range_exclude_high("wind speed", wind_speed, 0, 100);
  chk_if_in_range("azimuth angle", rel_aa, -180, 180);
  chk_vector_length("transmittance", "f_grid", transmittance, f_grid);
  if (fastem_version < 3 || fastem_version > 6)
    throw std::runtime_error(
        "Invalid fastem version: 3 <= fastem_version <= 6");
 
  emissivity.resize(nf, 4);
  reflectivity.resize(nf, 4);
 
  const Numeric t = max(surface_skin_t, Numeric(270));
 
  for (Index i = 0; i < nf; i++) {
    if (f_grid[i] > 250e9)
      throw std::runtime_error("Only frequency <= 250 GHz are allowed");
    chk_if_in_range("transmittance", transmittance[i], 0, 1);
 
    Vector e, r;
 
    fastem(e,
           r,
           f_grid[i],
           za,
           t,
           salinity,
           wind_speed,
           transmittance[i],
           rel_aa,
           fastem_version);
 
    emissivity(i, joker) = e;
    reflectivity(i, joker) = r;
  }
 
  // FASTEM does not work close to the horizon (at least v6). Make sure values
  // are inside [0,1]. Then seems best to make sure that e+r=1.
  for (Index i = 0; i < nf; i++) {
    for (Index s = 0; s < 2; s++) {
      if (emissivity(i, s) > 1) {
        emissivity(i, s) = 1;
        reflectivity(i, s) = 0;
      }
      if (emissivity(i, s) < 0) {
        emissivity(i, s) = 0;
        reflectivity(i, s) = 1;
      }
      if (reflectivity(i, s) > 1) {
        emissivity(i, s) = 0;
        reflectivity(i, s) = 1;
      }
      if (reflectivity(i, s) < 0) {
        emissivity(i, s) = 1;
        reflectivity(i, s) = 0;
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void InterpGriddedField2ToPosition(Numeric& outvalue,
                                   const Index& atmosphere_dim,
                                   const Vector& lat_grid,
                                   const Vector& lat_true,
                                   const Vector& lon_true,
                                   const Vector& rtp_pos,
                                   const GriddedField2& gfield2,
                                   const Verbosity&) {
  // Set expected order of grids
  Index gfield_latID = 0;
  Index gfield_lonID = 1;
 
  // Basic checks and sizes
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_latlon_true(atmosphere_dim, lat_grid, lat_true, lon_true);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  gfield2.checksize_strict();
  //
  chk_griddedfield_gridname(gfield2, gfield_latID, "Latitude");
  chk_griddedfield_gridname(gfield2, gfield_lonID, "Longitude");
  //
  const Index nlat = gfield2.data.nrows();
  const Index nlon = gfield2.data.ncols();
  //
  if (nlat < 2 || nlon < 2) {
    ostringstream os;
    os << "The data in *gfield2* must span a geographical region. That is,\n"
       << "the latitude and longitude grids must have a length >= 2.";
    throw runtime_error(os.str());
  }
 
  const Vector& GFlat = gfield2.get_numeric_grid(gfield_latID);
  const Vector& GFlon = gfield2.get_numeric_grid(gfield_lonID);
 
  // Determine true geographical position
  Vector lat(1), lon(1);
  pos2true_latlon(
      lat[0], lon[0], atmosphere_dim, lat_grid, lat_true, lon_true, rtp_pos);
 
  // Ensure correct coverage of lon grid
  Vector lon_shifted;
  lon_shiftgrid(lon_shifted, GFlon, lon[0]);
 
  // Check if lat/lon we need are actually covered
  chk_if_in_range("rtp_pos.lat", lat[0], GFlat[0], GFlat[nlat - 1]);
  chk_if_in_range("rtp_pos.lon", lon[0], lon_shifted[0], lon_shifted[nlon - 1]);
 
  // Interpolate in lat and lon
  //
  GridPos gp_lat, gp_lon;
  gridpos(gp_lat, GFlat, lat[0]);
  gridpos(gp_lon, lon_shifted, lon[0]);
  Vector itw(4);
  interpweights(itw, gp_lat, gp_lon);
  outvalue = interp(itw, gfield2.data, gp_lat, gp_lon);
}
 
 
/* Workspace method: Doxygen documentation will be auto-generated */
void InterpSurfaceFieldToPosition(Numeric& outvalue,
                                  const Index& atmosphere_dim,
                                  const Vector& lat_grid,
                                  const Vector& lon_grid,
                                  const Vector& rtp_pos,
                                  const Matrix& z_surface,
                                  const Matrix& field,
                                  const Verbosity& verbosity) {
  // Input checks (dummy p_grid)
  chk_atm_grids(atmosphere_dim, uniform_grid(2, 2, -1), lat_grid, lon_grid);
  chk_atm_surface(
      "input argument *field*", field, atmosphere_dim, lat_grid, lon_grid);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  //
  const Numeric zmax = max(z_surface);
  const Numeric zmin = min(z_surface);
  const Numeric dzok = 1;
  if (rtp_pos[0] < zmin - dzok || rtp_pos[0] > zmax + dzok) {
    ostringstream os;
    os << "The given position does not match *z_surface*.\nThe altitude in "
       << "*rtp_pos* is " << rtp_pos[0] / 1e3 << " km.\n"
       << "The altitude range covered by *z_surface* is [" << zmin / 1e3 << ","
       << zmax / 1e3 << "] km.\n"
       << "One possible mistake is to mix up *rtp_pos* and *rte_los*.";
    throw runtime_error(os.str());
  }
 
  if (atmosphere_dim == 1) {
    outvalue = field(0, 0);
  } else {
    chk_interpolation_grids("Latitude interpolation", lat_grid, rtp_pos[1]);
    GridPos gp_lat, gp_lon;
    gridpos(gp_lat, lat_grid, rtp_pos[1]);
    if (atmosphere_dim == 3) {
      chk_interpolation_grids("Longitude interpolation", lon_grid, rtp_pos[2]);
      gridpos(gp_lon, lon_grid, rtp_pos[2]);
    }
    //
    outvalue = interp_atmsurface_by_gp(atmosphere_dim, field, gp_lat, gp_lon);
  }
 
  // Interpolate
  CREATE_OUT3;
  out3 << "    Result = " << outvalue << "\n";
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceFastem(Workspace& ws,
                     Matrix& iy,
                     ArrayOfTensor3& diy_dx,
                     const Tensor3& iy_transmittance,
                     const Index& iy_id,
                     const Index& jacobian_do,
                     const Index& atmosphere_dim,
                     const EnergyLevelMap& nlte_field,
                     const Index& cloudbox_on,
                     const Index& stokes_dim,
                     const Vector& f_grid,
                     const Vector& rtp_pos,
                     const Vector& rtp_los,
                     const Vector& rte_pos2,
                     const String& iy_unit,
                     const Agenda& iy_main_agenda,
                     const Numeric& surface_skin_t,
                     const Numeric& salinity,
                     const Numeric& wind_speed,
                     const Numeric& wind_direction,
                     const Index& fastem_version,
                     const Verbosity& verbosity) {
  // Most obvious input checks are performed in specular_losCalc and surfaceFastem
 
  // Obtain radiance and transmission for specular direction
 
  // Determine specular direction
  Vector specular_los, surface_normal;
  specular_losCalcNoTopography(specular_los,
                               surface_normal,
                               rtp_pos,
                               rtp_los,
                               atmosphere_dim,
                               verbosity);
 
  // Use iy_aux to get optical depth for downwelling radiation.
  ArrayOfString iy_aux_vars(1);
  iy_aux_vars[0] = "Optical depth";
 
  // Calculate iy for downwelling radiation
  // Note that iy_transmittance used here lacks surface R. Fixed below.
  //
  const Index nf = f_grid.nelem();
  Vector transmittance(nf);
  Vector geo_pos;
  ArrayOfMatrix iy_aux;
  Ppath ppath;
  //
  iy_main_agendaExecute(ws,
                        iy,
                        iy_aux,
                        ppath,
                        diy_dx,
                        geo_pos,
                        0,
                        iy_transmittance,
                        iy_aux_vars,
                        iy_id,
                        iy_unit,
                        cloudbox_on,
                        jacobian_do,
                        f_grid,
                        nlte_field,
                        rtp_pos,
                        specular_los,
                        rte_pos2,
                        iy_main_agenda);
 
  // Convert tau to transmissions
  for (Index i = 0; i < nf; i++) {
    transmittance[i] = exp(-iy_aux[0](i, 0));
  }
 
  // Call Fastem by surface_RTprop version
  //
  Matrix surface_los;
  Tensor4 surface_rmatrix;
  Matrix surface_emission;
  //
  surfaceFastem(surface_los,
                surface_rmatrix,
                surface_emission,
                atmosphere_dim,
                stokes_dim,
                f_grid,
                rtp_pos,
                rtp_los,
                surface_skin_t,
                salinity,
                wind_speed,
                wind_direction,
                transmittance,
                fastem_version,
                verbosity);
 
  // Add up
  //
  Tensor3 I(1, nf, stokes_dim);
  I(0, joker, joker) = iy;
  Matrix sensor_los_dummy(1, 1, 0);
  //
  surface_calc(iy, I, sensor_los_dummy, surface_rmatrix, surface_emission);
 
  // Adjust diy_dx, if necessary.
  // For vector cases this is a slight approximation, as the order of the
  // different transmission and reflectivities matters.
  if (iy_transmittance.npages()) {
    for (Index q = 0; q < diy_dx.nelem(); q++) {
      for (Index p = 0; p < diy_dx[q].npages(); p++) {
        for (Index i = 0; i < nf; i++) {
          Vector x{diy_dx[q](p, i, joker)};
          mult(diy_dx[q](p, i, joker), surface_rmatrix(0, i, joker, joker), x);
        }
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceFlatReflectivity(Workspace& ws,
                         Matrix& iy,
                         ArrayOfTensor3& diy_dx,
                         ArrayOfTensor4& dsurface_rmatrix_dx,
                         ArrayOfMatrix& dsurface_emission_dx,
                         const Tensor3& iy_transmittance,
                         const Index& iy_id,
                         const Index& jacobian_do,
                         const Index& suns_do,
                         const Index& atmosphere_dim,
                         const EnergyLevelMap& nlte_field,
                         const Index& cloudbox_on,
                         const Index& stokes_dim,
                         const Vector& f_grid,
                         const Vector& lat_grid,
                         const Vector& lon_grid,
                         const Matrix& z_surface,
                         const Vector& refellipsoid,
                         const Vector& rtp_pos,
                         const Vector& rtp_los,
                         const Vector& rte_pos2,
                         const String& iy_unit,
                         const Tensor3& surface_reflectivity,
                         const Tensor3& surface_props_data,
                         const ArrayOfString& surface_props_names,
                         const ArrayOfString& dsurface_names,
                         const ArrayOfRetrievalQuantity& jacobian_quantities,
                         const Agenda& iy_main_agenda,
                         const Verbosity& verbosity) {
 
  // Input checks
  ARTS_USER_ERROR_IF(atmosphere_dim==2, "This method does not work for 2d atmospheres.")
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_size("iy",iy,f_grid.nelem(),stokes_dim);
 
  // Check surface_data
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  // Interplation grid positions and weights
  ArrayOfGridPos gp_lat(1), gp_lon(1);
  Matrix itw;
  rte_pos2gridpos(
      gp_lat[0], gp_lon[0], atmosphere_dim, lat_grid, lon_grid, rtp_pos);
  interp_atmsurface_gp2itw(itw, atmosphere_dim, gp_lat, gp_lon);
 
  // Skin temperature
  Vector surface_skin_t(1);
  surface_props_interp(surface_skin_t,
                       "Skin temperature",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  chk_not_negative("surface_skin_t", surface_skin_t[0]);
 
 
 
  //Allocate
  Tensor3 iy_trans_new;
  Matrix iy_incoming;
  Vector specular_los, surface_normal;
  ArrayOfMatrix iy_aux;
  Ppath ppath;
  ArrayOfTensor3 diy_dx_dumb;
  Matrix surface_los;
  Tensor4 surface_rmatrix;
  Matrix surface_emission;
  Tensor3 I(1,f_grid.nelem(),stokes_dim);
  if (iy_transmittance.npages()) {
    iy_trans_new=iy_transmittance;
  }
 
  //get specular line of sight
  specular_losCalc(specular_los,
                   surface_normal,
                   rtp_pos,
                   rtp_los,
                   atmosphere_dim,
                   lat_grid,
                   lon_grid,
                   refellipsoid,
                   z_surface,
                   0,
                   verbosity);
 
  // Calculate incoming radiation directions, surface reflection matrix and
  // emission vector
  surfaceFlatReflectivity(surface_los,
                          surface_rmatrix,
                          surface_emission,
                          f_grid,
                          stokes_dim,
                          atmosphere_dim,
                          rtp_pos,
                          rtp_los,
                          specular_los,
                          surface_skin_t[0],
                          surface_reflectivity,
                          verbosity);
 
 
 
  // Jacobian part
  if (jacobian_do) {
    dsurface_check(surface_props_names,
                   dsurface_names,
                   dsurface_rmatrix_dx,
                   dsurface_emission_dx);
 
    Index irq;
 
    // Skin temperature
    irq = find_first(dsurface_names, String("Skin temperature"));
    if (irq >= 0) {
      const Numeric dd = 0.1;
      Matrix surface_los2;
      surfaceFlatReflectivity(surface_los2,
                                    dsurface_rmatrix_dx[irq],
                                    dsurface_emission_dx[irq],
                                    f_grid,
                                    stokes_dim,
                                    atmosphere_dim,
                                    rtp_pos,
                                    rtp_los,
                                    specular_los,
                                    surface_skin_t[0]+dd,
                                    surface_reflectivity,
                                    verbosity);
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
  }
 
  iySurfaceRtpropCalc(ws,
                      iy,
                      diy_dx,
                      surface_los,
                      surface_rmatrix,
                      surface_emission,
                      dsurface_names,
                      dsurface_rmatrix_dx,
                      dsurface_emission_dx,
                      iy_transmittance,
                      iy_id,
                      jacobian_do,
                      suns_do,
                      jacobian_quantities,
                      atmosphere_dim,
                      nlte_field,
                      cloudbox_on,
                      stokes_dim,
                      f_grid,
                      rtp_pos,
                      rtp_los,
                      rte_pos2,
                      iy_unit,
                      iy_main_agenda,
                      verbosity);
 
 
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceFlatReflectivityDirect(
    Workspace& ws,
    Matrix& iy,
    const Vector& rtp_pos,
    const Vector& rtp_los,
    const Index& stokes_dim,
    const Vector& f_grid,
    const Index& atmosphere_dim,
    const Vector& p_grid,
    const Vector& lat_grid,
    const Vector& lon_grid,
    const Tensor3& z_field,
    const Tensor3& t_field,
    const EnergyLevelMap& nlte_field,
    const Tensor4& vmr_field,
    const ArrayOfArrayOfSpeciesTag& abs_species,
    const Tensor3& wind_u_field,
    const Tensor3& wind_v_field,
    const Tensor3& wind_w_field,
    const Tensor3& mag_u_field,
    const Tensor3& mag_v_field,
    const Tensor3& mag_w_field,
    const Matrix& z_surface,
    const Tensor3& surface_reflectivity,
    const Vector& refellipsoid,
    const Tensor4& pnd_field,
    const ArrayOfTensor4& dpnd_field_dx,
    const ArrayOfString& scat_species,
    const ArrayOfArrayOfSingleScatteringData& scat_data,
    const Numeric& ppath_lmax,
    const Numeric& ppath_lraytrace,
    const Index& ppath_inside_cloudbox_do,
    const Index& cloudbox_on,
    const ArrayOfIndex& cloudbox_limits,
    const Index& suns_do,
    const Index& gas_scattering_do,
    const Index& jacobian_do,
    const ArrayOfRetrievalQuantity& jacobian_quantities,
    const ArrayOfSun& suns,
    const Numeric& rte_alonglos_v,
    const String& iy_unit,
    const Agenda& propmat_clearsky_agenda,
    const Agenda& water_p_eq_agenda,
    const Agenda& gas_scattering_agenda,
    const Agenda& ppath_step_agenda,
    const Verbosity& verbosity) {
  //Check for correct unit
  ARTS_USER_ERROR_IF(iy_unit != "1" && suns_do,
                     "If suns are present only iy_unit=\"1\" can be used.");
 
  chk_size("iy", iy, f_grid.nelem(), stokes_dim);
 
  if (suns_do) {
    Matrix iy_incoming;
    Index suns_visible;
    Vector specular_los;
 
    //Get incoming direct radiation, if no sun is in line of sight, then
    //iy_incoming is zero.
    surface_get_incoming_direct(ws,
                                iy_incoming,
                                suns_visible,
                                specular_los,
                                rtp_pos,
                                rtp_los,
                                stokes_dim,
                                f_grid,
                                atmosphere_dim,
                                p_grid,
                                lat_grid,
                                lon_grid,
                                z_field,
                                t_field,
                                nlte_field,
                                vmr_field,
                                abs_species,
                                wind_u_field,
                                wind_v_field,
                                wind_w_field,
                                mag_u_field,
                                mag_v_field,
                                mag_w_field,
                                z_surface,
                                refellipsoid,
                                pnd_field,
                                dpnd_field_dx,
                                scat_species,
                                scat_data,
                                ppath_lmax,
                                ppath_lraytrace,
                                ppath_inside_cloudbox_do,
                                cloudbox_on,
                                cloudbox_limits,
                                gas_scattering_do,
                                jacobian_do,
                                jacobian_quantities,
                                suns,
                                rte_alonglos_v,
                                propmat_clearsky_agenda,
                                water_p_eq_agenda,
                                gas_scattering_agenda,
                                ppath_step_agenda,
                                verbosity);
 
    if (suns_visible) {
      Matrix surface_los;
      Tensor4 surface_rmatrix;
      Matrix surface_emission;
      Numeric surface_skin_t_dummy = 1.;
 
      //As we only consider the reflection of the direct radiation we do not consider
      //any type of surface emission, therefore we set the surface skin temperature
      //to a dummy value and later on set the surface emission vector (matrix) to zero.
      surfaceFlatReflectivity(surface_los,
                              surface_rmatrix,
                              surface_emission,
                              f_grid,
                              stokes_dim,
                              atmosphere_dim,
                              rtp_pos,
                              rtp_los,
                              specular_los,
                              surface_skin_t_dummy,
                              surface_reflectivity,
                              verbosity);
 
      surface_emission *= 0.;
 
      Tensor3 I(1, f_grid.nelem(), stokes_dim);
      I(0, joker, joker) = iy_incoming;
 
      surface_calc(iy, I, surface_los, surface_rmatrix, surface_emission);
 
      //TODO: add reflectivity jacobian
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceFlatRefractiveIndex(Workspace& ws,
                               Matrix& iy,
                               ArrayOfTensor3& diy_dx,
                               ArrayOfTensor4& dsurface_rmatrix_dx,
                               ArrayOfMatrix& dsurface_emission_dx,
                               const Tensor3& iy_transmittance,
                               const Index& iy_id,
                               const Index& jacobian_do,
                               const Index& suns_do,
                               const Index& atmosphere_dim,
                               const EnergyLevelMap& nlte_field,
                               const Index& cloudbox_on,
                               const Index& stokes_dim,
                               const Vector& f_grid,
                               const Vector& lat_grid,
                               const Vector& lon_grid,
                               const Matrix& z_surface,
                               const Vector& refellipsoid,
                               const Vector& rtp_pos,
                               const Vector& rtp_los,
                               const Vector& rte_pos2,
                               const String& iy_unit,
                               const GriddedField3& surface_complex_refr_index,
                               const Tensor3& surface_props_data,
                               const ArrayOfString& surface_props_names,
                               const ArrayOfString& dsurface_names,
                               const ArrayOfRetrievalQuantity& jacobian_quantities,
                               const Agenda& iy_main_agenda,
                               const Verbosity& verbosity) {
 
  // Input checks
  ARTS_USER_ERROR_IF(atmosphere_dim==2, "This method does not work for 2d atmospheres.")
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_size("iy",iy,f_grid.nelem(),stokes_dim);
 
  // Check surface_data
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  // Interplation grid positions and weights
  ArrayOfGridPos gp_lat(1), gp_lon(1);
  Matrix itw;
  rte_pos2gridpos(
      gp_lat[0], gp_lon[0], atmosphere_dim, lat_grid, lon_grid, rtp_pos);
  interp_atmsurface_gp2itw(itw, atmosphere_dim, gp_lat, gp_lon);
 
  // Skin temperature
  Vector surface_skin_t(1);
  surface_props_interp(surface_skin_t,
                       "Skin temperature",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  chk_not_negative("surface_skin_t", surface_skin_t[0]);
 
 
  //Allocate
  Tensor3 iy_trans_new;
  Matrix iy_incoming;
  Vector specular_los, surface_normal;
  ArrayOfMatrix iy_aux;
  Ppath ppath;
  ArrayOfTensor3 diy_dx_dumb;
  Matrix surface_los;
  Tensor4 surface_rmatrix;
  Matrix surface_emission;
  Tensor3 I(1,f_grid.nelem(),stokes_dim);
  if (iy_transmittance.npages()) {
    iy_trans_new=iy_transmittance;
  }
 
  //get specular line of sight
  specular_losCalc(specular_los,
                   surface_normal,
                   rtp_pos,
                   rtp_los,
                   atmosphere_dim,
                   lat_grid,
                   lon_grid,
                   refellipsoid,
                   z_surface,
                   0,
                   verbosity);
 
  // Calculate incoming radiation directions, surface reflection matrix and
  // emission vector
  surfaceFlatRefractiveIndex(surface_los,
                             surface_rmatrix,
                             surface_emission,
                             f_grid,
                             stokes_dim,
                             atmosphere_dim,
                             rtp_pos,
                             rtp_los,
                             specular_los,
                             surface_skin_t[0],
                             surface_complex_refr_index,
                             verbosity);
 
 
 
  // Jacobian part
  if (jacobian_do) {
    dsurface_check(surface_props_names,
                   dsurface_names,
                   dsurface_rmatrix_dx,
                   dsurface_emission_dx);
 
    Index irq;
 
    // Skin temperature
    irq = find_first(dsurface_names, String("Skin temperature"));
    if (irq >= 0) {
      const Numeric dd = 0.1;
      Matrix surface_los2;
      surfaceFlatRefractiveIndex(surface_los2,
                              dsurface_rmatrix_dx[irq],
                              dsurface_emission_dx[irq],
                              f_grid,
                              stokes_dim,
                              atmosphere_dim,
                              rtp_pos,
                              rtp_los,
                              specular_los,
                              surface_skin_t[0]+dd,
                                 surface_complex_refr_index,
                              verbosity);
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
  }
 
  iySurfaceRtpropCalc(ws,
                      iy,
                      diy_dx,
                      surface_los,
                      surface_rmatrix,
                      surface_emission,
                      dsurface_names,
                      dsurface_rmatrix_dx,
                      dsurface_emission_dx,
                      iy_transmittance,
                      iy_id,
                      jacobian_do,
                      suns_do,
                      jacobian_quantities,
                      atmosphere_dim,
                      nlte_field,
                      cloudbox_on,
                      stokes_dim,
                      f_grid,
                      rtp_pos,
                      rtp_los,
                      rte_pos2,
                      iy_unit,
                      iy_main_agenda,
                      verbosity);
 
 
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceFlatRefractiveIndexDirect(
    Workspace& ws,
    Matrix& iy,
    const Vector& rtp_pos,
    const Vector& rtp_los,
    const Index& stokes_dim,
    const Vector& f_grid,
    const Index& atmosphere_dim,
    const Vector& p_grid,
    const Vector& lat_grid,
    const Vector& lon_grid,
    const Tensor3& z_field,
    const Tensor3& t_field,
    const EnergyLevelMap& nlte_field,
    const Tensor4& vmr_field,
    const ArrayOfArrayOfSpeciesTag& abs_species,
    const Tensor3& wind_u_field,
    const Tensor3& wind_v_field,
    const Tensor3& wind_w_field,
    const Tensor3& mag_u_field,
    const Tensor3& mag_v_field,
    const Tensor3& mag_w_field,
    const Matrix& z_surface,
    const GriddedField3& surface_complex_refr_index,
    const Vector& refellipsoid,
    const Tensor4& pnd_field,
    const ArrayOfTensor4& dpnd_field_dx,
    const ArrayOfString& scat_species,
    const ArrayOfArrayOfSingleScatteringData& scat_data,
    const Numeric& ppath_lmax,
    const Numeric& ppath_lraytrace,
    const Index& ppath_inside_cloudbox_do,
    const Index& cloudbox_on,
    const ArrayOfIndex& cloudbox_limits,
    const Index& suns_do,
    const Index& gas_scattering_do,
    const Index& jacobian_do,
    const ArrayOfRetrievalQuantity& jacobian_quantities,
    const ArrayOfSun& suns,
    const Numeric& rte_alonglos_v,
    const String& iy_unit,
    const Agenda& propmat_clearsky_agenda,
    const Agenda& water_p_eq_agenda,
    const Agenda& gas_scattering_agenda,
    const Agenda& ppath_step_agenda,
    const Verbosity& verbosity) {
  //Check for correct unit
  ARTS_USER_ERROR_IF(iy_unit != "1" && suns_do,
                     "If suns are present only iy_unit=\"1\" can be used.");
 
  chk_size("iy", iy, f_grid.nelem(), stokes_dim);
 
  if (suns_do) {
    Matrix iy_incoming;
    Index suns_visible;
    Vector specular_los;
 
    //Get incoming direct radiation, if no sun is in line of sight, then
    //iy_incoming is zero.
    surface_get_incoming_direct(ws,
                                iy_incoming,
                                suns_visible,
                                specular_los,
                                rtp_pos,
                                rtp_los,
                                stokes_dim,
                                f_grid,
                                atmosphere_dim,
                                p_grid,
                                lat_grid,
                                lon_grid,
                                z_field,
                                t_field,
                                nlte_field,
                                vmr_field,
                                abs_species,
                                wind_u_field,
                                wind_v_field,
                                wind_w_field,
                                mag_u_field,
                                mag_v_field,
                                mag_w_field,
                                z_surface,
                                refellipsoid,
                                pnd_field,
                                dpnd_field_dx,
                                scat_species,
                                scat_data,
                                ppath_lmax,
                                ppath_lraytrace,
                                ppath_inside_cloudbox_do,
                                cloudbox_on,
                                cloudbox_limits,
                                gas_scattering_do,
                                jacobian_do,
                                jacobian_quantities,
                                suns,
                                rte_alonglos_v,
                                propmat_clearsky_agenda,
                                water_p_eq_agenda,
                                gas_scattering_agenda,
                                ppath_step_agenda,
                                verbosity);
 
    if (suns_visible) {
      Matrix surface_los;
      Tensor4 surface_rmatrix;
      Matrix surface_emission;
      Numeric surface_skin_t_dummy = 1.;
 
      //As we only consider the reflection of the direct radiation we do not consider
      //any type of surface emission, therefore we set the surface skin temperature
      //to a dummy value and later on set the surface emission vector (matrix) to zero.
     surfaceFlatRefractiveIndex(surface_los,
                                surface_rmatrix,
                                surface_emission,
                                f_grid,
                                stokes_dim,
                                atmosphere_dim,
                                rtp_pos,
                                rtp_los,
                                specular_los,
                                surface_skin_t_dummy,
                                surface_complex_refr_index,
                                verbosity);
 
      surface_emission *= 0.;
 
      Tensor3 I(1, f_grid.nelem(), stokes_dim);
      I(0, joker, joker) = iy_incoming;
 
      surface_calc(iy, I, surface_los, surface_rmatrix, surface_emission);
 
      //TODO: add reflectivity jacobian
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceInit(Matrix& iy,
                   const Vector& f_grid,
                   const Index& stokes_dim,
                   const Verbosity&) {
  iy.resize(f_grid.nelem(), stokes_dim);
  iy = 0.;
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceLambertian(Workspace& ws,
                         Matrix& iy,
                         ArrayOfTensor3& diy_dx,
                         const Tensor3& iy_transmittance,
                         const Index& iy_id,
                         const Index& jacobian_do,
                         const Index& suns_do,
                         const Index& atmosphere_dim,
                         const EnergyLevelMap& nlte_field,
                         const Index& cloudbox_on,
                         const Index& stokes_dim,
                         const Vector& f_grid,
                         const Vector& lat_grid,
                         const Vector& lon_grid,
                         const Matrix& z_surface,
                         const Vector& refellipsoid,
                         const Vector& rtp_pos,
                         const Vector& rtp_los,
                         const Vector& rte_pos2,
                         const String& iy_unit,
                         const Vector& surface_scalar_reflectivity,
                         const Tensor3& surface_props_data,
                         const ArrayOfString& surface_props_names,
                         const ArrayOfString& dsurface_names,
                         const ArrayOfRetrievalQuantity& jacobian_quantities,
                         const Agenda& iy_main_agenda,
                         const Index& N_za,
                         const Index& N_aa,
                         const Verbosity& verbosity) {
  // Input checks
  ARTS_USER_ERROR_IF(surface_scalar_reflectivity.nelem() != f_grid.nelem() &&
                     surface_scalar_reflectivity.nelem() != 1,
                     "The number of elements in *surface_scalar_reflectivity* should\n",
                     "match length of *f_grid* or be 1.",
                     "\n length of *f_grid* : ", f_grid.nelem(),
                     "\n length of *surface_scalar_reflectivity* : ",
                     surface_scalar_reflectivity.nelem());
  ARTS_USER_ERROR_IF(min(surface_scalar_reflectivity) < 0 ||
                         max(surface_scalar_reflectivity) > 1,
                     "All values in *surface_scalar_reflectivity* must be inside [0,1].");
  ARTS_USER_ERROR_IF(atmosphere_dim==2, "This method does not work for 2d atmospheres.");
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_size("iy",iy,f_grid.nelem(),stokes_dim);
 
  // Check surface_data
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  // Interplation grid positions and weights
  ArrayOfGridPos gp_lat(1), gp_lon(1);
  Matrix itw;
  rte_pos2gridpos(
      gp_lat[0], gp_lon[0], atmosphere_dim, lat_grid, lon_grid, rtp_pos);
  interp_atmsurface_gp2itw(itw, atmosphere_dim, gp_lat, gp_lon);
 
  // Skin temperature
  Vector surface_skin_t(1);
  surface_props_interp(surface_skin_t,
                       "Skin temperature",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  chk_not_negative("surface_skin_t", surface_skin_t[0]);
 
 
 
 
  const Index nf = f_grid.nelem();
 
  Vector za_grid, aa_grid, za_grid_weights;
 
  //get angular grids. here we use gauss quadrature. As the function is not intended for
  //a hemisphere but for full sphere, we have to tweak it a little bit and use only
  //the first half of the angles.
  AngularGridsSetFluxCalc(za_grid,
                          aa_grid,
                          za_grid_weights,
                          N_za * 2,
                          N_aa,
                          "double_gauss",
                          verbosity);
 
  Tensor3 iy_trans_new;
 
 
  ArrayOfString iy_aux_var(0);
  if (suns_do) {
    iy_aux_var.resize(1);
    iy_aux_var[0] = "Direct radiation";
  }
 
  Matrix iy_temp;
  Matrix Flx(nf, 1, 0.);
 
  if (iy_transmittance.npages()) {
    iy_trans_new=iy_transmittance;
  }
 
 
  ArrayOfTensor3 diy_dx_dumb;
  iy.resize(nf, stokes_dim);
  iy = 0;
 
  Vector los;
 
  //No azimuth dependency
  if (N_aa == 1) {
    //Set azimuth angle index
    Index i_aa = 0;
 
    for (Index i_za = 0; i_za < N_za; i_za++) {
 
      if (atmosphere_dim==1){
        los.resize(1);
      }
      else{
        los.resize(2);
        // For clearsky, the skylight is in general approximately independent of the azimuth direction.
        // So, we consider only the line of sight plane.
        los[1] = 0.;
      }
      los[0] = za_grid[i_za];
 
 
      // Calculate downwelling radiation for a los
      ArrayOfMatrix iy_aux;
      Ppath ppath;
      Vector geo_pos_dumb;
      Index iy_id_new = iy_id + i_za + i_aa * N_za + 1;
      iy_main_agendaExecute(ws,
                            iy_temp,
                            iy_aux,
                            ppath,
                            diy_dx_dumb,
                            geo_pos_dumb,
                            0,
                            iy_trans_new,
                            iy_aux_var,
                            iy_id_new,
                            iy_unit,
                            cloudbox_on,
                            jacobian_do,
                            f_grid,
                            nlte_field,
                            rtp_pos,
                            los,
                            rte_pos2,
                            iy_main_agenda);
 
      //For the case that a sun is present and the los is towards a sun, we
      //subtract the direct radiation, so that only the diffuse radiation is considered here.
      //If sun is within los iy_aux[0] is the incoming and attenuated direct (sun)
      //radiation at the surface. Otherwise,  it is zero.
      if (suns_do) {
        iy_temp -= iy_aux[0];
      }
      iy_temp *= abs(cos(deg2rad(los[0])) * sin(deg2rad(los[0]))) *
                 za_grid_weights[i_za];
      Flx(joker, 0) += iy_temp(joker, 0);
    }
    //Azimuthal integration just gives a factor of 2*pi
    Flx *= 2 * pi;
 
  //Azimuth dependency
  } else {
    // before we start with the actual RT calculation, we calculate the integration
    // weights for a trapezoidal integration over the azimuth.
    Vector aa_grid_weights;
    Vector aa_grid_rad = aa_grid;
 
    //For the integration we need the aa grid in rad
    for (Index i = 0; i < aa_grid_rad.nelem(); i++) {
      aa_grid_rad[i] = deg2rad(aa_grid_rad[i]);
    }
 
    calculate_int_weights_arbitrary_grid(aa_grid_weights, aa_grid_rad);
 
    //Allocate
    los.resize(2);
 
    for (Index i_aa = 0; i_aa < N_aa; i_aa++) {
      for (Index i_za = 0; i_za < N_za; i_za++) {
 
 
        los[0] = za_grid[i_za];
        los[1] = aa_grid[i_aa];
 
        // Calculate downwelling radiation for LOS ilos
        ArrayOfMatrix iy_aux;
        Ppath ppath;
        Vector geo_pos_dumb;
        Index iy_id_new = iy_id + i_za + i_aa * N_za + 1;
        iy_main_agendaExecute(ws,
                              iy_temp,
                              iy_aux,
                              ppath,
                              diy_dx_dumb,
                              geo_pos_dumb,
                              0,
                              iy_trans_new,
                              iy_aux_var,
                              iy_id_new,
                              iy_unit,
                              cloudbox_on,
                              jacobian_do,
                              f_grid,
                              nlte_field,
                              rtp_pos,
                              los,
                              rte_pos2,
                              iy_main_agenda);
 
        //For the case that a sun is present and the los is towards a sun, we
        //subtract the direct radiation, so that only the diffuse radiation is considered here.
        //If sun is within los iy_aux[0] is the incoming and attenuated direct (sun)
        //radiation at the surface. Otherwise it is zero.
        if (suns_do) {
          iy_temp -= iy_aux[0];
        }
        iy_temp *= abs(cos(deg2rad(los[0])) * sin(deg2rad(los[0]))) *
                   za_grid_weights[i_za] * aa_grid_weights[i_aa];
        Flx(joker, 0) += iy_temp(joker, 0);
      }
    }
  }
 
  Vector specular_los, surface_normal;
  specular_losCalc(specular_los,
                   surface_normal,
                   rtp_pos,
                   rtp_los,
                   atmosphere_dim,
                   lat_grid,
                   lon_grid,
                   refellipsoid,
                   z_surface,
                   0,
                   verbosity);
 
  //Surface emission
  Vector b(nf);
  planck(b, f_grid, surface_skin_t[0]);
 
  //Upwelling radiation
  Numeric r;
  for (Index i_freq = 0; i_freq < f_grid.nelem(); i_freq++) {
    if (i_freq == 0 || surface_scalar_reflectivity.nelem() > 1) {
      r = surface_scalar_reflectivity[i_freq];
    }
    iy(i_freq, 0) = r *
                        cos(deg2rad(specular_los[0])) / pi * Flx(i_freq, 0) +
                    (1 - r) * b[i_freq];
  }
 
  // Surface Jacobians
  if (jacobian_do && dsurface_names.nelem()) {
 
    Index irq;
    irq = find_first(dsurface_names, String("Skin temperature"));
 
    if (irq >= 0){
      // Find index among jacobian quantities
      Index ihit = -1;
      for (Index j = 0; j < jacobian_quantities.nelem() && ihit < 0; j++) {
        if (dsurface_names[irq] == jacobian_quantities[j].Subtag()) {
          ihit = j;
        }
      }
 
      // Derivative of surface skin temperature, as observed at the surface
      Matrix diy_dpos0(f_grid.nelem(), stokes_dim, 0.), diy_dpos;
      dplanck_dt(diy_dpos0(joker, 0), f_grid, surface_skin_t[0]);
 
      Vector emissivity=surface_scalar_reflectivity;
      emissivity*=-1;
      emissivity+=1;
      diy_dpos0*=ExhaustiveMatrixView{emissivity};
 
      // Weight with transmission to sensor
      iy_transmittance_mult(diy_dpos, iy_transmittance, diy_dpos0);
 
      // Put into diy_dx
      diy_from_pos_to_rgrids(diy_dx[ihit],
                             jacobian_quantities[ihit],
                             diy_dpos,
                             atmosphere_dim,
                             rtp_pos);
 
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceLambertianDirect(
    Workspace& ws,
    Matrix& iy,
    const Vector& rtp_pos,
    const Index& stokes_dim,
    const Vector& f_grid,
    const Index& atmosphere_dim,
    const Vector& p_grid,
    const Vector& lat_grid,
    const Vector& lon_grid,
    const Tensor3& z_field,
    const Tensor3& t_field,
    const EnergyLevelMap& nlte_field,
    const Tensor4& vmr_field,
    const ArrayOfArrayOfSpeciesTag& abs_species,
    const Tensor3& wind_u_field,
    const Tensor3& wind_v_field,
    const Tensor3& wind_w_field,
    const Tensor3& mag_u_field,
    const Tensor3& mag_v_field,
    const Tensor3& mag_w_field,
    const Matrix& z_surface,
    const Vector& surface_scalar_reflectivity,
    const Vector& refellipsoid,
    const Tensor4& pnd_field,
    const ArrayOfTensor4& dpnd_field_dx,
    const ArrayOfString& scat_species,
    const ArrayOfArrayOfSingleScatteringData& scat_data,
    const Numeric& ppath_lmax,
    const Numeric& ppath_lraytrace,
    const Index& cloudbox_on,
    const ArrayOfIndex& cloudbox_limits,
    const Index& suns_do,
    const Index& gas_scattering_do,
    const Index& jacobian_do,
    const ArrayOfRetrievalQuantity& jacobian_quantities,
    const ArrayOfSun& suns,
    const Numeric& rte_alonglos_v,
    const String& iy_unit,
    const Agenda& propmat_clearsky_agenda,
    const Agenda& water_p_eq_agenda,
    const Agenda& gas_scattering_agenda,
    const Agenda& ppath_step_agenda,
    const Verbosity& verbosity) {
  //Allocate
  ArrayOfVector sun_rte_los(suns.nelem());
  ArrayOfMatrix transmitted_sunlight;
  ArrayOfArrayOfTensor3 dtransmitted_sunlight;
  ArrayOfPpath sun_ppaths(suns.nelem());
  ArrayOfIndex suns_visible(suns.nelem());
 
  //Check for correct unit
  ARTS_USER_ERROR_IF(iy_unit != "1" && suns_do,
                     "If suns are present only iy_unit=\"1\" can be used.");
  //Check size of iy
  chk_size("iy",iy,f_grid.nelem(),stokes_dim);
 
  ARTS_USER_ERROR_IF(surface_scalar_reflectivity.nelem() != f_grid.nelem() &&
                         surface_scalar_reflectivity.nelem() != 1,
                     "The number of elements in *surface_scalar_reflectivity* should\n",
                     "match length of *f_grid* or be 1.",
                     "\n length of *f_grid* : ", f_grid.nelem(),
                     "\n length of *surface_scalar_reflectivity* : ",
                     surface_scalar_reflectivity.nelem());
  ARTS_USER_ERROR_IF(min(surface_scalar_reflectivity) < 0 ||
                         max(surface_scalar_reflectivity) > 1,
                     "All values in *surface_scalar_reflectivity* must be inside [0,1].");
  // Input checks
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
 
 
  //do something only if there is a sun
  if (suns_do) {
    //get sun ppaths
    get_sun_ppaths(ws,
                    sun_ppaths,
                    suns_visible,
                    sun_rte_los,
                    rtp_pos,
                    suns,
                    f_grid,
                    atmosphere_dim,
                    p_grid,
                    lat_grid,
                    lon_grid,
                    z_field,
                    z_surface,
                    refellipsoid,
                    ppath_lmax,
                    ppath_lraytrace,
                    ppath_step_agenda,
                    verbosity);
 
    get_direct_radiation(ws,
                         transmitted_sunlight,
                         dtransmitted_sunlight,
                         stokes_dim,
                         f_grid,
                         atmosphere_dim,
                         p_grid,
                         lat_grid,
                         lon_grid,
                         t_field,
                         nlte_field,
                         vmr_field,
                         abs_species,
                         wind_u_field,
                         wind_v_field,
                         wind_w_field,
                         mag_u_field,
                         mag_v_field,
                         mag_w_field,
                         cloudbox_on,
                         cloudbox_limits,
                         gas_scattering_do,
                         1,
                         sun_ppaths,
                         suns,
                         suns_visible,
                         refellipsoid,
                         pnd_field,
                         dpnd_field_dx,
                         scat_species,
                         scat_data,
                         jacobian_do,
                         jacobian_quantities,
                         propmat_clearsky_agenda,
                         water_p_eq_agenda,
                         gas_scattering_agenda,
                         rte_alonglos_v,
                         verbosity);
 
    //loop over suns
    Vector specular_los, surface_normal;
 
    for (Index i_sun = 0; i_sun < suns.nelem(); i_sun++) {
      if (suns_visible[i_sun]) {
        //sun_rte_los is the direction toward the sun, but we need from the sun
 
        Vector incoming_los;
        mirror_los(incoming_los,sun_rte_los[i_sun], atmosphere_dim);
 
        specular_losCalc(specular_los,
                         surface_normal,
                         rtp_pos,
                         incoming_los,
                         atmosphere_dim,
                         lat_grid,
                         lon_grid,
                         refellipsoid,
                         z_surface,
                         0,
                         verbosity);
 
        // Only the first component of transmitted_sunlight is relevant.
        // Comment taken from surfaceLambertianSimple.
        // This follows VDISORT that refers to: K. L. Coulson, Polarization and Intensity of Light in
        // the Atmosphere (1989), page 229
        // (Thanks to Michael Kahnert for providing this information!)
        // Update: Is the above for a later edition? We have not found a copy of
        // that edition. In a 1988 version of the book, the relevant page seems
        // to be 232.
 
        Vector iy_surface_direct(f_grid.nelem());
        Numeric r;
        for (Index i_freq = 0; i_freq < f_grid.nelem(); i_freq++) {
          if (i_freq == 0 || surface_scalar_reflectivity.nelem() > 1) {
            r = surface_scalar_reflectivity[i_freq];
          }
          iy_surface_direct[i_freq] = r / pi *
                                      transmitted_sunlight[i_sun](i_freq, 0) *
                                      cos(deg2rad(specular_los[0]));
        }
 
        //Add the surface contribution of the direct part
        iy(joker, 0) += iy_surface_direct;
 
 
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceRtpropAgenda(Workspace& ws,
                           Matrix& iy,
                           ArrayOfTensor3& diy_dx,
                           Numeric& surface_skin_t,
                           Matrix& surface_los,
                           Tensor4& surface_rmatrix,
                           Matrix& surface_emission,
                           const Tensor3& iy_transmittance,
                           const Index& iy_id,
                           const Index& jacobian_do,
                           const Index& suns_do,
                           const Index& atmosphere_dim,
                           const EnergyLevelMap& nlte_field,
                           const Index& cloudbox_on,
                           const Index& stokes_dim,
                           const Vector& f_grid,
                           const Vector& rtp_pos,
                           const Vector& rtp_los,
                           const Vector& rte_pos2,
                           const String& iy_unit,
                           const Agenda& iy_main_agenda,
                           const Agenda& surface_rtprop_agenda,
                           const Verbosity&) {
  // Input checks
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
 
  // Call *surface_rtprop_agenda*
  surface_rtprop_agendaExecute(ws,
                               surface_skin_t,
                               surface_emission,
                               surface_los,
                               surface_rmatrix,
                               f_grid,
                               rtp_pos,
                               rtp_los,
                               surface_rtprop_agenda);
 
  // Check output of *surface_rtprop_agenda*
  const Index nlos = surface_los.nrows();
  const Index nf = f_grid.nelem();
  //
  if (nlos)  // if 0, blackbody ground and not all checks are needed
  {
    if (surface_los.ncols() != rtp_los.nelem())
      throw runtime_error("Number of columns in *surface_los* is not correct.");
    if (nlos != surface_rmatrix.nbooks())
      throw runtime_error(
          "Mismatch in size of *surface_los* and *surface_rmatrix*.");
    if (surface_rmatrix.npages() != nf)
      throw runtime_error(
          "Mismatch in size of *surface_rmatrix* and *f_grid*.");
    if (surface_rmatrix.nrows() != stokes_dim ||
        surface_rmatrix.ncols() != stokes_dim)
      throw runtime_error(
          "Mismatch between size of *surface_rmatrix* and *stokes_dim*.");
  }
  if (surface_emission.ncols() != stokes_dim)
    throw runtime_error(
        "Mismatch between size of *surface_emission* and *stokes_dim*.");
  if (surface_emission.nrows() != nf)
    throw runtime_error("Mismatch in size of *surface_emission* and f_grid*.");
 
  // Variable to hold down-welling radiation
  Tensor3 I(nlos, nf, stokes_dim);
 
  ArrayOfString iy_aux_var(0);
  if (suns_do) iy_aux_var.emplace_back("Direct radiation");
 
  // Loop *surface_los*-es. If no such LOS, we are ready.
  if (nlos > 0) {
    for (Index ilos = 0; ilos < nlos; ilos++) {
      Vector los{surface_los(ilos, joker)};
 
      // Include surface reflection matrix in *iy_transmittance*
      // If iy_transmittance is empty, this is interpreted as the
      // variable is not needed.
      //
      Tensor3 iy_trans_new;
      //
      if (iy_transmittance.npages()) {
        iy_transmittance_mult(iy_trans_new,
                             iy_transmittance,
                             surface_rmatrix(ilos, joker, joker, joker));
      }
 
      // Calculate downwelling radiation for LOS ilos
      //
      {
        ArrayOfMatrix iy_aux;
        Ppath ppath;
        Vector geo_pos;
        Index iy_id_new = iy_id + ilos + 1;
        iy_main_agendaExecute(ws,
                              iy,
                              iy_aux,
                              ppath,
                              diy_dx,
                              geo_pos,
                              0,
                              iy_trans_new,
                              iy_aux_var,
                              iy_id_new,
                              iy_unit,
                              cloudbox_on,
                              jacobian_do,
                              f_grid,
                              nlte_field,
                              rtp_pos,
                              los,
                              rte_pos2,
                              iy_main_agenda);
 
        //For the case that a sun is present and the los is towards a sun, we
        //subtract the direct radiation, so that only the diffuse radiation is considered here.
        //If sun is within los iy_aux[0] is the incoming and attenuated direct (sun)
        //radiation at the surface. Otherwise it is zero.
        if (suns_do){
          iy-=iy_aux[0];
        }
 
      }
 
      if (iy.ncols() != stokes_dim || iy.nrows() != nf) {
        ostringstream os;
        os << "The size of *iy* returned from *" << iy_main_agenda.name()
           << "* is\n"
           << "not correct:\n"
           << "  expected size = [" << nf << "," << stokes_dim << "]\n"
           << "  size of iy    = [" << iy.nrows() << "," << iy.ncols() << "]\n";
        throw runtime_error(os.str());
      }
 
      I(ilos, joker, joker) = iy;
    }
  }
 
  // Add up
  surface_calc(iy, I, surface_los, surface_rmatrix, surface_emission);
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void iySurfaceRtpropCalc(Workspace& ws,
                         Matrix& iy,
                         ArrayOfTensor3& diy_dx,
                         const Matrix& surface_los,
                         const Tensor4& surface_rmatrix,
                         const Matrix& surface_emission,
                         const ArrayOfString& dsurface_names,
                         const ArrayOfTensor4& dsurface_rmatrix_dx,
                         const ArrayOfMatrix& dsurface_emission_dx,
                         const Tensor3& iy_transmittance,
                         const Index& iy_id,
                         const Index& jacobian_do,
                         const Index& suns_do,
                         const ArrayOfRetrievalQuantity& jacobian_quantities,
                         const Index& atmosphere_dim,
                         const EnergyLevelMap& nlte_field,                         
                         const Index& cloudbox_on,
                         const Index& stokes_dim,
                         const Vector& f_grid,
                         const Vector& rtp_pos,
                         const Vector& rtp_los,
                         const Vector& rte_pos2,
                         const String& iy_unit,
                         const Agenda& iy_main_agenda,
                         const Verbosity&) {
  // Input checks
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
 
  // Check provided surface rtprop variables
  const Index nlos = surface_los.nrows();
  const Index nf = f_grid.nelem();
  //
  if (nlos)  // if 0, blackbody ground and not all checks are needed
  {
    if (surface_los.ncols() != rtp_los.nelem())
      throw runtime_error("Number of columns in *surface_los* is not correct.");
    if (nlos != surface_rmatrix.nbooks())
      throw runtime_error(
          "Mismatch in size of *surface_los* and *surface_rmatrix*.");
    if (surface_rmatrix.npages() != nf)
      throw runtime_error(
          "Mismatch in size of *surface_rmatrix* and *f_grid*.");
    if (surface_rmatrix.nrows() != stokes_dim ||
        surface_rmatrix.ncols() != stokes_dim)
      throw runtime_error(
          "Mismatch between size of *surface_rmatrix* and *stokes_dim*.");
  }
  if (surface_emission.ncols() != stokes_dim)
    throw runtime_error(
        "Mismatch between size of *surface_emission* and *stokes_dim*.");
  if (surface_emission.nrows() != nf)
    throw runtime_error("Mismatch in size of *surface_emission* and f_grid*.");
 
  // Variable to hold down-welling radiation
  Tensor3 I(nlos, nf, stokes_dim);
 
  ArrayOfString iy_aux_var(0);
  if (suns_do) iy_aux_var.emplace_back("Direct radiation");
 
  // Loop *surface_los*-es.
  if (nlos > 0) {
    for (Index ilos = 0; ilos < nlos; ilos++) {
      Vector los{surface_los(ilos, joker)};
 
      // Include surface reflection matrix in *iy_transmittance*
      // If iy_transmittance is empty, this is interpreted as the
      // variable is not needed.
      //
      Tensor3 iy_trans_new;
      //
      if (iy_transmittance.npages()) {
        iy_transmittance_mult(iy_trans_new,
                             iy_transmittance,
                             surface_rmatrix(ilos, joker, joker, joker));
      }
 
      // Calculate downwelling radiation for LOS ilos
      //
      {
        ArrayOfMatrix iy_aux;
        Ppath ppath;
        Vector geo_pos;
        iy_main_agendaExecute(ws,
                              iy,
                              iy_aux,
                              ppath,
                              diy_dx,
                              geo_pos,
                              0,
                              iy_trans_new,
                              iy_aux_var,
                              iy_id,
                              iy_unit,
                              cloudbox_on,
                              jacobian_do,
                              f_grid,
                              nlte_field,
                              rtp_pos,
                              los,
                              rte_pos2,
                              iy_main_agenda);
 
        //For the case that a sun is present and the los is towards a sun, we
        //subtract the direct radiation, so that only the diffuse radiation is considered here.
        //If sun is within los iy_aux[0] is the incoming and attenuated direct (sun)
        //radiation at the surface. Otherwise it is zero.
        if (suns_do){
          iy-=iy_aux[0];
        }
 
      }
 
      if (iy.ncols() != stokes_dim || iy.nrows() != nf) {
        ostringstream os;
        os << "The size of *iy* returned from *" << iy_main_agenda.name()
           << "* is\n"
           << "not correct:\n"
           << "  expected size = [" << nf << "," << stokes_dim << "]\n"
           << "  size of iy    = [" << iy.nrows() << "," << iy.ncols() << "]\n";
        throw runtime_error(os.str());
      }
 
      I(ilos, joker, joker) = iy;
    }
  }
 
  // Add up
  surface_calc(iy, I, surface_los, surface_rmatrix, surface_emission);
 
  // Surface Jacobians
  if (jacobian_do && dsurface_names.nelem()) {
    // Loop dsurface_names
    for (Index i = 0; i < dsurface_names.nelem(); i++) {
      // Error if derivatives not calculated
      // Or should we accept this?
      if (dsurface_emission_dx[i].empty() || dsurface_rmatrix_dx[i].empty()) {
        ostringstream os;
        os << "The derivatives for surface quantity: " << dsurface_names[i]
           << "\nwere not calculated by *iy_surface_agenda*.\n"
           << "That is, *dsurface_emission_dx* and/or *dsurface_rmatrix_dx*\n"
           << "are empty.";
        throw runtime_error(os.str());
      } else {
        // Find index among jacobian quantities
        Index ihit = -1;
        for (Index j = 0; j < jacobian_quantities.nelem() && ihit < 0; j++) {
          if (dsurface_names[i] == jacobian_quantities[j].Subtag()) {
            ihit = j;
          }
        }
        ARTS_ASSERT(ihit >= 0);
        // Derivative, as observed at the surface
        Matrix diy_dpos0, diy_dpos;
        surface_calc(diy_dpos0,
                     I,
                     surface_los,
                     dsurface_rmatrix_dx[i],
                     dsurface_emission_dx[i]);
        // Weight with transmission to sensor
        iy_transmittance_mult(diy_dpos, iy_transmittance, diy_dpos0);
        // Put into diy_dx
        diy_from_pos_to_rgrids(diy_dx[ihit],
                               jacobian_quantities[ihit],
                               diy_dpos,
                               atmosphere_dim,
                               rtp_pos);
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void specular_losCalcNoTopography(Vector& specular_los,
                                  Vector& surface_normal,
                                  const Vector& rtp_pos,
                                  const Vector& rtp_los,
                                  const Index& atmosphere_dim,
                                  const Verbosity&) {
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
 
  surface_normal.resize(max(Index(1), atmosphere_dim - 1));
  specular_los.resize(max(Index(1), atmosphere_dim - 1));
 
  if (atmosphere_dim == 1) {
    surface_normal[0] = 0;
    if (rtp_los[0] < 90) {
      throw runtime_error(
          "Invalid zenith angle. The zenith angle corresponds "
          "to observe the surface from below.");
    }
    specular_los[0] = 180 - rtp_los[0];
  }
 
  else if (atmosphere_dim == 2) {
    specular_los[0] = sign(rtp_los[0]) * 180 - rtp_los[0];
    surface_normal[0] = 0;
  }
 
  else if (atmosphere_dim == 3) {
    specular_los[0] = 180 - rtp_los[0];
    specular_los[1] = rtp_los[1];
    surface_normal[0] = 0;
    surface_normal[1] = 0;
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void specular_losCalc(Vector& specular_los,
                      Vector& surface_normal,
                      const Vector& rtp_pos,
                      const Vector& rtp_los,
                      const Index& atmosphere_dim,
                      const Vector& lat_grid,
                      const Vector& lon_grid,
                      const Vector& refellipsoid,
                      const Matrix& z_surface,
                      const Index& ignore_surface_slope,
                      const Verbosity& verbosity) {
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_if_in_range("ignore_surface_slope", ignore_surface_slope, 0, 1);
 
  // Use special function if there is no slope, or it is ignored
  if (atmosphere_dim == 1 || ignore_surface_slope) {
    specular_losCalcNoTopography(specular_los,
                                 surface_normal,
                                 rtp_pos,
                                 rtp_los,
                                 atmosphere_dim,
                                 verbosity);
    return;
  }
 
  surface_normal.resize(max(Index(1), atmosphere_dim - 1));
  specular_los.resize(max(Index(1), atmosphere_dim - 1));
 
  if (atmosphere_dim == 2) {
    chk_interpolation_grids("Latitude interpolation", lat_grid, rtp_pos[1]);
    GridPos gp_lat;
    gridpos(gp_lat, lat_grid, rtp_pos[1]);
    Numeric c1;  // Radial slope of the surface
    plevel_slope_2d(
        c1, lat_grid, refellipsoid, z_surface(joker, 0), gp_lat, rtp_los[0]);
    Vector itw(2);
    interpweights(itw, gp_lat);
    const Numeric rv_surface = refell2d(refellipsoid, lat_grid, gp_lat) +
                               interp(itw, z_surface(joker, 0), gp_lat);
    surface_normal[0] = -plevel_angletilt(rv_surface, c1);
    if (abs(rtp_los[0] - surface_normal[0]) < 90) {
      throw runtime_error(
          "Invalid zenith angle. The zenith angle corresponds "
          "to observe the surface from below.");
    }
    specular_los[0] =
        sign(rtp_los[0]) * 180 - rtp_los[0] + 2 * surface_normal[0];
  }
 
  else {
    // Calculate surface normal in South-North direction
    chk_interpolation_grids("Latitude interpolation", lat_grid, rtp_pos[1]);
    chk_interpolation_grids("Longitude interpolation", lon_grid, rtp_pos[2]);
    GridPos gp_lat, gp_lon;
    gridpos(gp_lat, lat_grid, rtp_pos[1]);
    gridpos(gp_lon, lon_grid, rtp_pos[2]);
    Numeric c1, c2;
    plevel_slope_3d(
        c1, c2, lat_grid, lon_grid, refellipsoid, z_surface, gp_lat, gp_lon, 0);
    Vector itw(4);
    interpweights(itw, gp_lat, gp_lon);
    const Numeric rv_surface = refell2d(refellipsoid, lat_grid, gp_lat) +
                               interp(itw, z_surface, gp_lat, gp_lon);
    const Numeric zaSN = 90 - plevel_angletilt(rv_surface, c1);
    // The same for East-West
    plevel_slope_3d(c1,
                    c2,
                    lat_grid,
                    lon_grid,
                    refellipsoid,
                    z_surface,
                    gp_lat,
                    gp_lon,
                    90);
    const Numeric zaEW = 90 - plevel_angletilt(rv_surface, c1);
    // Convert to Cartesian, and determine normal by cross-product
    Vector tangentSN(3), tangentEW(3), normal(3);
    zaaa2cart(tangentSN[0], tangentSN[1], tangentSN[2], zaSN, 0);
    zaaa2cart(tangentEW[0], tangentEW[1], tangentEW[2], zaEW, 90);
    cross3(normal, tangentSN, tangentEW);
    // Convert rtp_los to cartesian and flip direction
    Vector di(3);
    zaaa2cart(di[0], di[1], di[2], rtp_los[0], rtp_los[1]);
    di *= -1;
    // Set LOS normal vector
    cart2zaaa(
        surface_normal[0], surface_normal[1], normal[0], normal[1], normal[2]);
    if (abs(rtp_los[0] - surface_normal[0]) < 90) {
      throw runtime_error(
          "Invalid zenith angle. The zenith angle corresponds "
          "to observe the surface from below.");
    }
    // Specular direction is 2(dn*di)dn-di, where dn is the normal vector
    Vector speccart(3);
    const Numeric fac = 2 * (normal * di);
    for (Index i = 0; i < 3; i++) {
      speccart[i] = fac * normal[i] - di[i];
    }
    cart2zaaa(specular_los[0],
              specular_los[1],
              speccart[0],
              speccart[1],
              speccart[2]);
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceBlackbody(Matrix& surface_los,
                      Tensor4& surface_rmatrix,
                      Matrix& surface_emission,
                      const Index& atmosphere_dim,
                      const Vector& f_grid,
                      const Index& stokes_dim,
                      const Vector& rtp_pos,
                      const Vector& rtp_los,
                      const Numeric& surface_skin_t,
                      const Verbosity& verbosity) {
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_not_negative("surface_skin_t", surface_skin_t);
 
  CREATE_OUT2;
  out2 << "  Sets variables to model a blackbody surface with a temperature "
       << " of " << surface_skin_t << " K.\n";
 
  surface_los.resize(0, 0);
  surface_rmatrix.resize(0, 0, 0, 0);
 
  const Index nf = f_grid.nelem();
 
  Vector b(nf);
  planck(b, f_grid, surface_skin_t);
 
  surface_emission.resize(nf, stokes_dim);
  surface_emission = 0.0;
 
  for (Index iv = 0; iv < nf; iv++) {
    surface_emission(iv, 0) = b[iv];
    for (Index is = 1; is < stokes_dim; is++) {
      surface_emission(iv, is) = 0;
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceFastem(Matrix& surface_los,
                   Tensor4& surface_rmatrix,
                   Matrix& surface_emission,
                   const Index& atmosphere_dim,
                   const Index& stokes_dim,
                   const Vector& f_grid,
                   const Vector& rtp_pos,
                   const Vector& rtp_los,
                   const Numeric& surface_skin_t,
                   const Numeric& salinity,
                   const Numeric& wind_speed,
                   const Numeric& wind_direction,
                   const Vector& transmittance,
                   const Index& fastem_version,
                   const Verbosity& verbosity) {
  // Input checks
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_if_in_range("wind_direction", wind_direction, -180, 180);
 
  const Index nf = f_grid.nelem();
 
  // Determine specular direction
  Vector specular_los, surface_normal;
  specular_losCalcNoTopography(specular_los,
                               surface_normal,
                               rtp_pos,
                               rtp_los,
                               atmosphere_dim,
                               verbosity);
 
  // Determine relative azimuth
  //
  // According to email from James Hocking, UkMet:
  // All azimuth angles are defined as being measured clockwise from north
  // (i.e. if the projection onto the Earth's surface of the view path lies due
  // north the azimuth angle is 0 and if it lies due east the azimuth angle is
  // 90 degrees). The relative azimuth is the wind direction (azimuth) angle
  // minus the satellite azimuth angle.
  Numeric rel_azimuth = wind_direction;  // Always true for 1D
  if (atmosphere_dim == 2 && rtp_los[0] < 0) {
    rel_azimuth -= 180;
    resolve_lon(rel_azimuth, -180, 180);
  } else if (atmosphere_dim == 3) {
    rel_azimuth -= rtp_los[1];
    resolve_lon(rel_azimuth, -180, 180);
  }
 
  // Call FASTEM
  Matrix emissivity, reflectivity;
  FastemStandAlone(emissivity,
                   reflectivity,
                   f_grid,
                   surface_skin_t,
                   abs(rtp_los[0]),
                   salinity,
                   wind_speed,
                   rel_azimuth,
                   transmittance,
                   fastem_version,
                   verbosity);
 
  // Set surface_los
  surface_los.resize(1, specular_los.nelem());
  surface_los(0, joker) = specular_los;
 
  // Surface emission
  //
  Vector b(nf);
  planck(b, f_grid, surface_skin_t);
  //
  surface_emission.resize(nf, stokes_dim);
  for (Index i = 0; i < nf; i++) {
    // I
    surface_emission(i, 0) = b[i] * 0.5 * (emissivity(i, 0) + emissivity(i, 1));
    // Q
    if (stokes_dim >= 2) {
      surface_emission(i, 1) =
          b[i] * 0.5 * (emissivity(i, 0) - emissivity(i, 1));
    }
    // U and V
    for (Index j = 2; j < stokes_dim; j++) {
      surface_emission(i, j) = b[i] * emissivity(i, j);
    }
  }
 
  // Surface reflectivity matrix
  //
  surface_rmatrix.resize(1, nf, stokes_dim, stokes_dim);
  surface_rmatrix = 0.0;
  for (Index iv = 0; iv < nf; iv++) {
    surface_rmatrix(0, iv, 0, 0) =
        0.5 * (reflectivity(iv, 0) + reflectivity(iv, 1));
    if (stokes_dim >= 2) {
      surface_rmatrix(0, iv, 0, 1) =
          0.5 * (reflectivity(iv, 0) - reflectivity(iv, 1));
      ;
      surface_rmatrix(0, iv, 1, 0) = surface_rmatrix(0, iv, 0, 1);
      surface_rmatrix(0, iv, 1, 1) = surface_rmatrix(0, iv, 0, 0);
 
      for (Index i = 2; i < stokes_dim; i++) {
        surface_rmatrix(0, iv, i, i) = surface_rmatrix(0, iv, 0, 0);
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceMapToLinearPolarisation(Matrix& surface_emission,
                                    Tensor4& surface_rmatrix,
                                    const Index& stokes_dim,
                                    const Numeric& pol_angle,
                                    const Verbosity& ) {
  ARTS_USER_ERROR_IF (stokes_dim != 1,
        "You should only use this method where the main calculations are "
        "done with *stokes_dim* set to 1.");
  
  Index local_stokes = surface_emission.ncols();
  ARTS_USER_ERROR_IF (local_stokes < 2,
        "This method requires that the input surface proporties match a Stokes "
        "dimension of 2-4. Incoming *surface_emission* matches stokes_dim=1.");
 
  const Index nf = surface_emission.nrows();
  const Index nlos = surface_rmatrix.nbooks();
  Matrix se = surface_emission;
  Tensor4 sr = surface_rmatrix;
  surface_emission.resize(nf, 1);
  surface_rmatrix.resize(nlos, nf, 1, 1);
  
  if (local_stokes == 2) {
    const Numeric alpha = DEG2RAD * pol_angle; 
    const Numeric c2 = pow( cos(alpha), 2 );
    const Numeric s2 = pow( sin(alpha), 2 );
    for (Index f=0; f<nf; ++f) {
      const Numeric bv = se(f,0) + se(f,1); // Note that we have to multiply with 2
      const Numeric bh = se(f,0) - se(f,1); // as we place a single pol as I
      surface_emission(f,0) = c2*bv + s2*bh;
      for (Index l=0; l<nlos; ++l) {
        const Numeric rv = sr(l,f,0,0) + sr(l,f,1,0); 
        const Numeric rh = sr(l,f,0,0) - sr(l,f,1,0);
        surface_rmatrix(l,f,0,0) = c2*rv + s2*rh;
      }
    }
  } else {
    Matrix Cm, Cs, Lp, Lm;
    mueller_stokes2modif(Cm, local_stokes);
    mueller_modif2stokes(Cs, local_stokes);
    mueller_rotation(Lp, local_stokes, pol_angle);
    mueller_rotation(Lm, local_stokes, -pol_angle);
    Matrix Mleft(local_stokes,local_stokes), Mright(local_stokes,local_stokes);
    mult(Mleft, Cm, Lp);
    mult(Mright, Lm, Cs);
    //
    Vector Vr(local_stokes);
    Matrix Tmp(local_stokes,local_stokes), Mr(local_stokes,local_stokes);
    //
    for (Index f=0; f<nf; ++f) {
      mult(Vr, Mleft, se(f,joker) );        // Note that we have to multiply with 2
      surface_emission(f,0) = 2.0 * Vr[0];  // as we place a single pol as I
      for (Index l=0; l<nlos; ++l) {
        mult(Tmp, sr(l,f,joker,joker), Mright);
        mult(Mr, Mleft, Tmp);
        surface_rmatrix(l,f,0,0) = Tmp(0,0);
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceTelsem(Matrix& surface_los,
                   Tensor4& surface_rmatrix,
                   Matrix& surface_emission,
                   const Index& atmosphere_dim,
                   const Index& stokes_dim,
                   const Vector& f_grid,
                   const Vector& lat_grid,
                   const Vector& lat_true,
                   const Vector& lon_true,
                   const Vector& rtp_pos,
                   const Vector& rtp_los,
                   const Vector& specular_los,
                   const Numeric& surface_skin_t,
                   const TelsemAtlas& atlas,
                   const Numeric& r_min,
                   const Numeric& r_max,
                   const Numeric& d_max,
                   const Verbosity& verbosity) {
  // Input checks
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_rte_los(atmosphere_dim, specular_los);
  chk_if_in_range_exclude(
      "surface skin temperature", surface_skin_t, 190.0, 373.0);
 
  const Index nf = f_grid.nelem();
  Matrix surface_rv_rh(nf, 2);
 
  // Lookup cell in atlas.
 
  Numeric lat, lon;
  pos2true_latlon(
      lat, lon, atmosphere_dim, lat_grid, lat_true, lon_true, rtp_pos);
  chk_if_in_range("Latitude input to TELSEM2", lat, -90.0, 90.0);
 
  lon = fmod(lon, 360.0);
  if (lon < 0) {
    lon += 360.0;
  }
  chk_if_in_range("Longitude input to TELSEM2", lon, 0.0, 360.0);
 
  Index cellnumber = atlas.calc_cellnum(lat, lon);
  // Check if cell is in atlas.
  if (!atlas.contains(cellnumber)) {
    if (d_max <= 0.0) {
      throw std::runtime_error(
          "Given coordinates are not contained in "
          " TELSEM atlas. To enable nearest neighbour"
          "interpolation set *d_max* to a positive "
          "value.");
    } else {
      cellnumber = atlas.calc_cellnum_nearest_neighbor(lat, lon);
      Numeric lat_nn, lon_nn;
      std::tie(lat_nn, lon_nn) = atlas.get_coordinates(cellnumber);
      Numeric d = sphdist(lat, lon, lat_nn, lon_nn);
      if (d > d_max) {
        std::ostringstream out{};
        out << "Distance of nearest neighbour exceeds provided limit (";
        out << d << " > " << d_max << ").";
        throw std::runtime_error(out.str());
      }
    }
  }
 
  Index class1 = atlas.get_class1(cellnumber);
  Index class2 = atlas.get_class2(cellnumber);
 
  Vector emis_h = atlas.get_emis_h(cellnumber);
  Vector emis_v = atlas.get_emis_v(cellnumber);
  Numeric e_v, e_h;
 
  // Incidence angle
  const Numeric theta = calc_incang(rtp_los, specular_los);
  ARTS_ASSERT(theta <= 90);
 
  for (Index i = 0; i < nf; ++i) {
    if (f_grid[i] < 5e9)
      throw std::runtime_error("Only frequency >= 5 GHz are allowed");
    if (f_grid[i] > 900e9)
      throw std::runtime_error("Only frequency <= 900 GHz are allowed");
 
    // For frequencies 700 <= f <= 900 GHz use 700 GHz to avoid extrapolation
    // outside of TELSEM specifications.
    Numeric f = std::min(f_grid[i], 700e9) * 1e-9;
    std::tie(e_v, e_h) =
        atlas.emis_interp(theta, f, class1, class2, emis_v, emis_h);
 
    surface_rv_rh(i, 0) = min(max(1.0 - e_v, r_min), r_max);
    surface_rv_rh(i, 1) = min(max(1.0 - e_h, r_min), r_max);
  }
 
  surfaceFlatRvRh(surface_los,
                  surface_rmatrix,
                  surface_emission,
                  f_grid,
                  stokes_dim,
                  atmosphere_dim,
                  rtp_pos,
                  rtp_los,
                  specular_los,
                  surface_skin_t,
                  surface_rv_rh,
                  verbosity);
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceTessem(Matrix& surface_los,
                   Tensor4& surface_rmatrix,
                   Matrix& surface_emission,
                   const Index& atmosphere_dim,
                   const Index& stokes_dim,
                   const Vector& f_grid,
                   const Vector& rtp_pos,
                   const Vector& rtp_los,
                   const Numeric& surface_skin_t,
                   const TessemNN& net_h,
                   const TessemNN& net_v,
                   const Numeric& salinity,
                   const Numeric& wind_speed,
                   const Verbosity& verbosity) {
  // Input checks
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_if_in_range_exclude(
      "surface skin temperature", surface_skin_t, 260.0, 373.0);
  chk_if_in_range_exclude_high("salinity", salinity, 0, 1);
  chk_if_in_range_exclude_high("wind speed", wind_speed, 0, 100);
 
  // Determine specular direction
  Vector specular_los, surface_normal;
  specular_losCalcNoTopography(specular_los,
                               surface_normal,
                               rtp_pos,
                               rtp_los,
                               atmosphere_dim,
                               verbosity);
 
  // TESSEM in and out
  //
  Vector out(2);
  VectorView e_h = out[Range(0, 1)];
  VectorView e_v = out[Range(1, 1)];
  //
  Vector in(5);
  in[1] = 180.0 - abs(rtp_los[0]);
  in[2] = wind_speed;
  in[3] = surface_skin_t;
  in[4] = salinity;
 
  // Get Rv and Rh
  //
  const Index nf = f_grid.nelem();
  Matrix surface_rv_rh(nf, 2);
  //
  for (Index i = 0; i < nf; ++i) {
    if (f_grid[i] < 5e9)
      throw std::runtime_error("Only frequency >= 5 GHz are allowed");
    if (f_grid[i] > 900e9)
      throw std::runtime_error("Only frequency <= 900 GHz are allowed");
 
    in[0] = f_grid[i];
 
    tessem_prop_nn(e_h, net_h, in);
    tessem_prop_nn(e_v, net_v, in);
 
    surface_rv_rh(i, 0) = min(max(1 - e_v[0], (Numeric)0), (Numeric)1);
    surface_rv_rh(i, 1) = min(max(1 - e_h[0], (Numeric)0), (Numeric)1);
  }
 
  surfaceFlatRvRh(surface_los,
                  surface_rmatrix,
                  surface_emission,
                  f_grid,
                  stokes_dim,
                  atmosphere_dim,
                  rtp_pos,
                  rtp_los,
                  specular_los,
                  surface_skin_t,
                  surface_rv_rh,
                  verbosity);
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceFlatRefractiveIndex(Matrix& surface_los,
                                Tensor4& surface_rmatrix,
                                Matrix& surface_emission,
                                const Vector& f_grid,
                                const Index& stokes_dim,
                                const Index& atmosphere_dim,
                                const Vector& rtp_pos,
                                const Vector& rtp_los,
                                const Vector& specular_los,
                                const Numeric& surface_skin_t,
                                const GriddedField3& surface_complex_refr_index,
                                const Verbosity& verbosity) {
  CREATE_OUT2;
  CREATE_OUT3;
 
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_rte_los(atmosphere_dim, specular_los);
  chk_not_negative("surface_skin_t", surface_skin_t);
 
  // Interpolate *surface_complex_refr_index*
  //
  const Index nf = f_grid.nelem();
  //
  Matrix n_real(nf, 1), n_imag(nf, 1);
  //
  complex_n_interp(n_real,
                   n_imag,
                   surface_complex_refr_index,
                   "surface_complex_refr_index",
                   f_grid,
                   Vector(1, surface_skin_t));
 
  out2 << "  Sets variables to model a flat surface\n";
  out3 << "     surface temperature: " << surface_skin_t << " K.\n";
 
  surface_los.resize(1, specular_los.nelem());
  surface_los(0, joker) = specular_los;
 
  surface_emission.resize(nf, stokes_dim);
  surface_rmatrix.resize(1, nf, stokes_dim, stokes_dim);
 
  // Incidence angle
  const Numeric incang = calc_incang(rtp_los, specular_los);
  ARTS_ASSERT(incang <= 90);
 
  // Complex (amplitude) reflection coefficients
  Complex Rv, Rh;
 
  for (Index iv = 0; iv < nf; iv++) {
    // Set n2 (refractive index of surface medium)
    Complex n2(n_real(iv, 0), n_imag(iv, 0));
 
    // Amplitude reflection coefficients
    fresnel(Rv, Rh, Numeric(1.0), n2, incang);
 
    // Fill reflection matrix and emission vector
    surface_specular_R_and_b(surface_rmatrix(0, iv, joker, joker),
                             surface_emission(iv, joker),
                             Rv,
                             Rh,
                             f_grid[iv],
                             stokes_dim,
                             surface_skin_t);
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceFlatReflectivity(Matrix& surface_los,
                             Tensor4& surface_rmatrix,
                             Matrix& surface_emission,
                             const Vector& f_grid,
                             const Index& stokes_dim,
                             const Index& atmosphere_dim,
                             const Vector& rtp_pos,
                             const Vector& rtp_los,
                             const Vector& specular_los,
                             const Numeric& surface_skin_t,
                             const Tensor3& surface_reflectivity,
                             const Verbosity& verbosity) {
  CREATE_OUT2;
 
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_rte_los(atmosphere_dim, specular_los);
  chk_not_negative("surface_skin_t", surface_skin_t);
 
  const Index nf = f_grid.nelem();
 
  if (surface_reflectivity.nrows() != stokes_dim &&
      surface_reflectivity.ncols() != stokes_dim) {
    ostringstream os;
    os << "The number of rows and columnss in *surface_reflectivity* must\n"
       << "match *stokes_dim*."
       << "\n stokes_dim : " << stokes_dim
       << "\n number of rows in *surface_reflectivity* : "
       << surface_reflectivity.nrows()
       << "\n number of columns in *surface_reflectivity* : "
       << surface_reflectivity.ncols() << "\n";
    throw runtime_error(os.str());
  }
 
  if (surface_reflectivity.npages() != nf &&
      surface_reflectivity.npages() != 1) {
    ostringstream os;
    os << "The number of pages in *surface_reflectivity* should\n"
       << "match length of *f_grid* or be 1."
       << "\n length of *f_grid* : " << nf
       << "\n dimension of *surface_reflectivity* : "
       << surface_reflectivity.npages() << "\n";
    throw runtime_error(os.str());
  }
 
  out2 << "  Sets variables to model a flat surface\n";
 
  surface_los.resize(1, specular_los.nelem());
  surface_los(0, joker) = specular_los;
 
  surface_emission.resize(nf, stokes_dim);
  surface_rmatrix.resize(1, nf, stokes_dim, stokes_dim);
 
  Matrix R, IR(stokes_dim, stokes_dim);
 
  Vector b(nf);
  planck(b, f_grid, surface_skin_t);
 
  Vector B(stokes_dim, 0);
 
  for (Index iv = 0; iv < nf; iv++) {
    if (iv == 0 || surface_reflectivity.npages() > 1) {
      R = surface_reflectivity(iv, joker, joker);
      for (Index i = 0; i < stokes_dim; i++) {
        for (Index j = 0; j < stokes_dim; j++) {
          if (i == j) {
            IR(i, j) = 1 - R(i, j);
          } else {
            IR(i, j) = -R(i, j);
          }
        }
      }
    }
 
    surface_rmatrix(0, iv, joker, joker) = R;
 
    B[0] = b[iv];
    mult(surface_emission(iv, joker), IR, B);
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceFlatRvRh(Matrix& surface_los,
                     Tensor4& surface_rmatrix,
                     Matrix& surface_emission,
                     const Vector& f_grid,
                     const Index& stokes_dim,
                     const Index& atmosphere_dim,
                     const Vector& rtp_pos,
                     const Vector& rtp_los,
                     const Vector& specular_los,
                     const Numeric& surface_skin_t,
                     const Matrix& surface_rv_rh,
                     const Verbosity&) {
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_rte_los(atmosphere_dim, specular_los);
  chk_not_negative("surface_skin_t", surface_skin_t);
 
  const Index nf = f_grid.nelem();
 
  if (surface_rv_rh.ncols() != 2) {
    ostringstream os;
    os << "The number of columns in *surface_rv_rh* must be two,\n"
       << "but the actual number of columns is " << surface_rv_rh.ncols()
       << "\n";
    throw runtime_error(os.str());
  }
 
  if (surface_rv_rh.nrows() != nf && surface_rv_rh.nrows() != 1) {
    ostringstream os;
    os << "The number of rows in *surface_rv_rh* should\n"
       << "match length of *f_grid* or be 1."
       << "\n length of *f_grid* : " << nf
       << "\n rows in *surface_rv_rh* : " << surface_rv_rh.nrows() << "\n";
    throw runtime_error(os.str());
  }
 
  if (min(surface_rv_rh) < 0 || max(surface_rv_rh) > 1) {
    throw runtime_error("All values in *surface_rv_rh* must be inside [0,1].");
  }
 
  surface_los.resize(1, specular_los.nelem());
  surface_los(0, joker) = specular_los;
 
  surface_emission.resize(nf, stokes_dim);
  surface_rmatrix.resize(1, nf, stokes_dim, stokes_dim);
 
  surface_emission = 0;
  surface_rmatrix = 0;
 
  Vector b(nf);
  planck(b, f_grid, surface_skin_t);
 
  Numeric rmean = 0.0, rdiff = 0.0;
 
  for (Index iv = 0; iv < nf; iv++) {
    if (iv == 0 || surface_rv_rh.nrows() > 1) {
      rmean = 0.5 * (surface_rv_rh(iv, 0) + surface_rv_rh(iv, 1));
      rdiff = 0.5 * (surface_rv_rh(iv, 0) - surface_rv_rh(iv, 1));
    }
 
    surface_emission(iv, 0) = (1.0 - rmean) * b[iv];
    surface_rmatrix(0, iv, 0, 0) = rmean;
 
    if (stokes_dim > 1) {
      surface_emission(iv, 1) = -rdiff * b[iv];
 
      surface_rmatrix(0, iv, 0, 1) = rdiff;
      surface_rmatrix(0, iv, 1, 0) = rdiff;
      surface_rmatrix(0, iv, 1, 1) = rmean;
 
      for (Index i = 2; i < stokes_dim; i++) {
        surface_rmatrix(0, iv, i, i) = rmean;
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceFlatScalarReflectivity(Matrix& surface_los,
                                   Tensor4& surface_rmatrix,
                                   Matrix& surface_emission,
                                   const Vector& f_grid,
                                   const Index& stokes_dim,
                                   const Index& atmosphere_dim,
                                   const Vector& rtp_pos,
                                   const Vector& rtp_los,
                                   const Vector& specular_los,
                                   const Numeric& surface_skin_t,
                                   const Vector& surface_scalar_reflectivity,
                                   const Verbosity&) {
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_rte_los(atmosphere_dim, specular_los);
  chk_not_negative("surface_skin_t", surface_skin_t);
 
  const Index nf = f_grid.nelem();
 
  if (surface_scalar_reflectivity.nelem() != nf &&
      surface_scalar_reflectivity.nelem() != 1) {
    ostringstream os;
    os << "The number of elements in *surface_scalar_reflectivity* should\n"
       << "match length of *f_grid* or be 1."
       << "\n length of *f_grid* : " << nf
       << "\n length of *surface_scalar_reflectivity* : "
       << surface_scalar_reflectivity.nelem() << "\n";
    throw runtime_error(os.str());
  }
 
  if (min(surface_scalar_reflectivity) < 0 ||
      max(surface_scalar_reflectivity) > 1) {
    throw runtime_error(
        "All values in *surface_scalar_reflectivity* must be inside [0,1].");
  }
 
  surface_los.resize(1, specular_los.nelem());
  surface_los(0, joker) = specular_los;
 
  surface_emission.resize(nf, stokes_dim);
  surface_rmatrix.resize(1, nf, stokes_dim, stokes_dim);
 
  surface_emission = 0;
  surface_rmatrix = 0;
 
  Vector b(nf);
  planck(b, f_grid, surface_skin_t);
 
  Numeric r = 0.0;
 
  for (Index iv = 0; iv < nf; iv++) {
    if (iv == 0 || surface_scalar_reflectivity.nelem() > 1) {
      r = surface_scalar_reflectivity[iv];
    }
 
    surface_emission(iv, 0) = (1.0 - r) * b[iv];
    surface_rmatrix(0, iv, 0, 0) = r;
    for (Index i = 1; i < stokes_dim; i++) {
      surface_rmatrix(0, iv, i, i) = r;
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surfaceLambertianSimple(Matrix& surface_los,
                             Tensor4& surface_rmatrix,
                             Matrix& surface_emission,
                             const Vector& f_grid,
                             const Index& stokes_dim,
                             const Index& atmosphere_dim,
                             const Vector& rtp_pos,
                             const Vector& rtp_los,
                             const Vector& surface_normal,
                             const Numeric& surface_skin_t,
                             const Vector& surface_scalar_reflectivity,
                             const Index& lambertian_nza,
                             const Numeric& za_pos,
                             const Verbosity&) {
  const Index nf = f_grid.nelem();
 
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  chk_not_negative("surface_skin_t", surface_skin_t);
  chk_if_in_range("za_pos", za_pos, 0, 1);
 
  if (surface_scalar_reflectivity.nelem() != nf &&
      surface_scalar_reflectivity.nelem() != 1) {
    ostringstream os;
    os << "The number of elements in *surface_scalar_reflectivity* should\n"
       << "match length of *f_grid* or be 1."
       << "\n length of *f_grid* : " << nf
       << "\n length of *surface_scalar_reflectivity* : "
       << surface_scalar_reflectivity.nelem() << "\n";
    throw runtime_error(os.str());
  }
 
  if (min(surface_scalar_reflectivity) < 0 ||
      max(surface_scalar_reflectivity) > 1) {
    throw runtime_error(
        "All values in *surface_scalar_reflectivity* must be inside [0,1].");
  }
 
  // Allocate and init everything to zero
  //
  surface_los.resize(lambertian_nza, rtp_los.nelem());
  surface_rmatrix.resize(lambertian_nza, nf, stokes_dim, stokes_dim);
  surface_emission.resize(nf, stokes_dim);
  //
  surface_los = 0.0;
  surface_rmatrix = 0.0;
  surface_emission = 0.0;
 
  // Help variables
  //
  const Numeric dza = (90.0 - abs(surface_normal[0])) / (Numeric)lambertian_nza;
  const Vector za_lims=uniform_grid(0.0, lambertian_nza + 1, dza);
 
  // surface_los
  for (Index ip = 0; ip < lambertian_nza; ip++) {
    surface_los(ip, 0) = za_lims[ip] + za_pos * dza;
    if (atmosphere_dim == 2) {
      if (rtp_los[0] < 0) {
        surface_los(ip, 0) *= -1.0;
      }
 
    } else if (atmosphere_dim == 3) {
      surface_los(ip, 1) = rtp_los[1];
    }
  }
 
  Vector b(nf);
  planck(b, f_grid, surface_skin_t);
 
  // Loop frequencies and set remaining values
  //
  Numeric r = 0.0;
  //
  for (Index iv = 0; iv < nf; iv++) {
    // Get reflectivity
    if (iv == 0 || surface_scalar_reflectivity.nelem() > 1) {
      r = surface_scalar_reflectivity[iv];
    }
 
    // surface_rmatrix:
    // Only element (0,0) is set to be non-zero. This follows VDISORT
    // that refers to: K. L. Coulson, Polarization and Intensity of Light in
    // the Atmosphere (1989), page 229
    // (Thanks to Michael Kahnert for providing this information!)
    // Update: Is the above for a later edition? We have not found a copy of
    // that edition. In a 1988 version of the book, the relevant page seems
    // to be 232.
    for (Index ip = 0; ip < lambertian_nza; ip++) {
      const Numeric w =
          r * 0.5 *
          (cos(2 * DEG2RAD * za_lims[ip]) - cos(2 * DEG2RAD * za_lims[ip + 1]));
      surface_rmatrix(ip, iv, 0, 0) = w;
    }
 
    // surface_emission
    surface_emission(iv, 0) = (1 - r) * b[iv];
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_complex_refr_indexFromGriddedField5(
    GriddedField3& surface_complex_refr_index,
    const Index& atmosphere_dim,
    const Vector& lat_grid,
    const Vector& lat_true,
    const Vector& lon_true,
    const Vector& rtp_pos,
    const GriddedField5& complex_n_field,
    const Verbosity&) {
  // Set expected order of grids
  Index gfield_fID = 0;
  Index gfield_tID = 1;
  Index gfield_compID = 2;
  Index gfield_latID = 3;
  Index gfield_lonID = 4;
 
  // Basic checks and sizes
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_latlon_true(atmosphere_dim, lat_grid, lat_true, lon_true);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  complex_n_field.checksize_strict();
  //
  chk_griddedfield_gridname(complex_n_field, gfield_fID, "Frequency");
  chk_griddedfield_gridname(complex_n_field, gfield_tID, "Temperature");
  chk_griddedfield_gridname(complex_n_field, gfield_compID, "Complex");
  chk_griddedfield_gridname(complex_n_field, gfield_latID, "Latitude");
  chk_griddedfield_gridname(complex_n_field, gfield_lonID, "Longitude");
  //
  const Index nf = complex_n_field.data.nshelves();
  const Index nt = complex_n_field.data.nbooks();
  const Index nn = complex_n_field.data.npages();
  const Index nlat = complex_n_field.data.nrows();
  const Index nlon = complex_n_field.data.ncols();
  //
  if (nlat < 2 || nlon < 2) {
    ostringstream os;
    os << "The data in *complex_refr_index_field* must span a geographical "
       << "region. That is,\nthe latitude and longitude grids must have a "
       << "length >= 2.";
    throw runtime_error(os.str());
  }
  //
  if (nn != 2) {
    ostringstream os;
    os << "The data in *complex_refr_index_field* must have exactly two "
       << "pages. One page each\nfor the real and imaginary part of the "
       << "complex refractive index.";
    throw runtime_error(os.str());
  }
 
  const Vector& GFlat = complex_n_field.get_numeric_grid(gfield_latID);
  const Vector& GFlon = complex_n_field.get_numeric_grid(gfield_lonID);
 
  // Determine true geographical position
  Vector lat(1), lon(1);
  pos2true_latlon(
      lat[0], lon[0], atmosphere_dim, lat_grid, lat_true, lon_true, rtp_pos);
 
  // Ensure correct coverage of lon grid
  Vector lon_shifted;
  lon_shiftgrid(lon_shifted, GFlon, lon[0]);
 
  // Check if lat/lon we need are actually covered
  chk_if_in_range("rtp_pos.lat", lat[0], GFlat[0], GFlat[nlat - 1]);
  chk_if_in_range("rtp_pos.lon", lon[0], lon_shifted[0], lon_shifted[nlon - 1]);
 
  // Size and fills grids of *surface_complex_refr_index*
  surface_complex_refr_index.resize(nf, nt, 2);
  surface_complex_refr_index.set_grid_name(0, "Frequency");
  surface_complex_refr_index.set_grid(
      0, complex_n_field.get_numeric_grid(gfield_fID));
  surface_complex_refr_index.set_grid_name(1, "Temperature");
  surface_complex_refr_index.set_grid(
      1, complex_n_field.get_numeric_grid(gfield_tID));
  surface_complex_refr_index.set_grid_name(2, "Complex");
  surface_complex_refr_index.set_grid(2, {"real", "imaginary"});
 
  // Interpolate in lat and lon
  //
  GridPos gp_lat, gp_lon;
  gridpos(gp_lat, GFlat, lat[0]);
  gridpos(gp_lon, lon_shifted, lon[0]);
  Vector itw(4);
  interpweights(itw, gp_lat, gp_lon);
  //
  for (Index iv = 0; iv < nf; iv++) {
    for (Index it = 0; it < nt; it++) {
      surface_complex_refr_index.data(iv, it, 0) = interp(
          itw, complex_n_field.data(iv, it, 0, joker, joker), gp_lat, gp_lon);
      surface_complex_refr_index.data(iv, it, 1) = interp(
          itw, complex_n_field.data(iv, it, 1, joker, joker), gp_lat, gp_lon);
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_reflectivityFromGriddedField6(Tensor3& surface_reflectivity,
                                           const Index& stokes_dim,
                                           const Vector& f_grid,
                                           const Index& atmosphere_dim,
                                           const Vector& lat_grid,
                                           const Vector& lat_true,
                                           const Vector& lon_true,
                                           const Vector& rtp_pos,
                                           const Vector& rtp_los,
                                           const GriddedField6& r_field,
                                           const Verbosity&) {
  // Basic checks and sizes
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_if_in_range("stokes_dim", stokes_dim, 1, 4);
  chk_latlon_true(atmosphere_dim, lat_grid, lat_true, lon_true);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  r_field.checksize_strict();
  chk_griddedfield_gridname(r_field, 0, "Frequency");
  chk_griddedfield_gridname(r_field, 1, "Stokes element");
  chk_griddedfield_gridname(r_field, 2, "Stokes element");
  chk_griddedfield_gridname(r_field, 3, "Incidence angle");
  chk_griddedfield_gridname(r_field, 4, "Latitude");
  chk_griddedfield_gridname(r_field, 5, "Longitude");
  //
  const Index nf_in = r_field.data.nvitrines();
  const Index ns2 = r_field.data.nshelves();
  const Index ns1 = r_field.data.nbooks();
  const Index nza = r_field.data.npages();
  const Index nlat = r_field.data.nrows();
  const Index nlon = r_field.data.ncols();
  //
  if (nlat < 2 || nlon < 2) {
    ostringstream os;
    os << "The data in *r_field* must span a geographical region. That is,\n"
       << "the latitude and longitude grids must have a length >= 2.";
    throw runtime_error(os.str());
  }
  //
  if (nza < 2) {
    ostringstream os;
    os << "The data in *r_field* must span a range of zenith angles. That\n"
       << "is the zenith angle grid must have a length >= 2.";
    throw runtime_error(os.str());
  }
  if (ns1 < stokes_dim || ns2 < stokes_dim || ns1 > 4 || ns2 > 4) {
    ostringstream os;
    os << "The \"Stokes dimensions\" must have a size that is >= "
       << "*stokes_dim* (but not exceeding 4).";
    throw runtime_error(os.str());
  }
 
  // Determine true geographical position
  Vector lat(1), lon(1);
  pos2true_latlon(
      lat[0], lon[0], atmosphere_dim, lat_grid, lat_true, lon_true, rtp_pos);
 
  // Ensure correct coverage of lon grid
  Vector lon_shifted;
  lon_shiftgrid(lon_shifted, r_field.get_numeric_grid(5), lon[0]);
 
  // Interpolate in lat and lon
  Tensor4 r_f_za(nf_in, stokes_dim, stokes_dim, nza);
  {
    chk_interpolation_grids(
        "Latitude interpolation", r_field.get_numeric_grid(4), lat[0]);
    chk_interpolation_grids("Longitude interpolation", lon_shifted, lon[0]);
    GridPos gp_lat, gp_lon;
    gridpos(gp_lat, r_field.get_numeric_grid(4), lat[0]);
    gridpos(gp_lon, lon_shifted, lon[0]);
    Vector itw(4);
    interpweights(itw, gp_lat, gp_lon);
    for (Index iv = 0; iv < nf_in; iv++) {
      for (Index iz = 0; iz < nza; iz++) {
        for (Index is1 = 0; is1 < stokes_dim; is1++) {
          for (Index is2 = 0; is2 < stokes_dim; is2++) {
            r_f_za(iv, is1, is2, iz) =
                interp(itw,
                       r_field.data(iv, is1, is2, iz, joker, joker),
                       gp_lat,
                       gp_lon);
          }
        }
      }
    }
  }
 
  // Interpolate in incidence angle, cubic if possible
  Tensor3 r_f(nf_in, stokes_dim, stokes_dim);
  Index order = 3;
  if (nza < 4) {
    order = 1;
  }
  {
    chk_interpolation_grids(
      "Incidence angle interpolation", r_field.get_numeric_grid(3), 180 - rtp_los[0]);
    const LagrangeInterpolation lag(0, 180 - rtp_los[0], r_field.get_numeric_grid(3), order);
    const auto itw = interpweights(lag);
    //
    for (Index i = 0; i < nf_in; i++) {
      for (Index is1 = 0; is1 < stokes_dim; is1++) {
        for (Index is2 = 0; is2 < stokes_dim; is2++) {
          r_f(i, is1, is2) = interp(r_f_za(i, is1, is2, joker), itw, lag);
        }
      }
    }
  }
 
  // Extract or interpolate in frequency
  //
  if (nf_in == 1) {
    surface_reflectivity = r_f;
  } else {
    chk_interpolation_grids(
        "Frequency interpolation", r_field.get_numeric_grid(0), f_grid);
    const Index nf_out = f_grid.nelem();
    surface_reflectivity.resize(nf_out, stokes_dim, stokes_dim);
    //
    ArrayOfGridPos gp(nf_out);
    Matrix itw(nf_out, 2);
    gridpos(gp, r_field.get_numeric_grid(0), f_grid);
    interpweights(itw, gp);
    for (Index is1 = 0; is1 < stokes_dim; is1++) {
      for (Index is2 = 0; is2 < stokes_dim; is2++) {
        interp(surface_reflectivity(joker, is1, is2),
               itw,
               r_f(joker, is1, is2),
               gp);
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_scalar_reflectivityFromGriddedField4(
    Vector& surface_scalar_reflectivity,
    const Index& stokes_dim,
    const Vector& f_grid,
    const Index& atmosphere_dim,
    const Vector& lat_grid,
    const Vector& lat_true,
    const Vector& lon_true,
    const Vector& rtp_pos,
    const Vector& rtp_los,
    const GriddedField4& r_field,
    const Verbosity&) {
  // Basic checks and sizes
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_if_in_range("stokes_dim", stokes_dim, 1, 1);
  chk_latlon_true(atmosphere_dim, lat_grid, lat_true, lon_true);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  chk_rte_los(atmosphere_dim, rtp_los);
  r_field.checksize_strict();
  chk_griddedfield_gridname(r_field, 0, "Frequency");
  chk_griddedfield_gridname(r_field, 1, "Incidence angle");
  chk_griddedfield_gridname(r_field, 2, "Latitude");
  chk_griddedfield_gridname(r_field, 3, "Longitude");
  //
  const Index nf_in = r_field.data.nbooks();
  const Index nza = r_field.data.npages();
  const Index nlat = r_field.data.nrows();
  const Index nlon = r_field.data.ncols();
  //
  if (nlat < 2 || nlon < 2) {
    ostringstream os;
    os << "The data in *r_field* must span a geographical region. That is,\n"
       << "the latitude and longitude grids must have a length >= 2.";
    throw runtime_error(os.str());
  }
  //
  if (nza < 2) {
    ostringstream os;
    os << "The data in *r_field* must span a range of zenith angles. That\n"
       << "is the zenith angle grid must have a length >= 2.";
    throw runtime_error(os.str());
  }
 
  // Determine true geographical position
  Vector lat(1), lon(1);
  pos2true_latlon(
      lat[0], lon[0], atmosphere_dim, lat_grid, lat_true, lon_true, rtp_pos);
 
  // Ensure correct coverage of lon grid
  Vector lon_shifted;
  lon_shiftgrid(lon_shifted, r_field.get_numeric_grid(3), lon[0]);
 
  // Interpolate in lat and lon
  Matrix r_f_za(nf_in, nza);
  {
    chk_interpolation_grids(
        "Latitude interpolation", r_field.get_numeric_grid(2), lat[0]);
    chk_interpolation_grids("Longitude interpolation", lon_shifted, lon[0]);
    GridPos gp_lat, gp_lon;
    gridpos(gp_lat, r_field.get_numeric_grid(2), lat[0]);
    gridpos(gp_lon, lon_shifted, lon[0]);
    Vector itw(4);
    interpweights(itw, gp_lat, gp_lon);
    for (Index iv = 0; iv < nf_in; iv++) {
      for (Index iz = 0; iz < nza; iz++) {
        r_f_za(iv, iz) =
            interp(itw, r_field.data(iv, iz, joker, joker), gp_lat, gp_lon);
      }
    }
  }
 
  // Interpolate in incidence angle, cubic if possible
  Vector r_f(nf_in);
  Index order = 3;
  if (nza < 4) {
    order = 1;
  }
  {
    chk_interpolation_grids(
      "Incidence angle interpolation", r_field.get_numeric_grid(1), 180 - rtp_los[0]);
    const LagrangeInterpolation lag(0, 180 - rtp_los[0], r_field.get_numeric_grid(1), order);
    const auto itw=interpweights(lag);
    for (Index i = 0; i < nf_in; i++) {
      r_f[i] = interp(r_f_za(i, joker), itw, lag);
    }
  }
 
  // Extract or interpolate in frequency
  //
  if (nf_in == 1) {
    surface_scalar_reflectivity.resize(1);
    surface_scalar_reflectivity[0] = r_f[0];
  } else {
    chk_interpolation_grids(
        "Frequency interpolation", r_field.get_numeric_grid(0), f_grid);
    const Index nf_out = f_grid.nelem();
    surface_scalar_reflectivity.resize(nf_out);
    //
    ArrayOfGridPos gp(nf_out);
    Matrix itw(nf_out, 2);
    gridpos(gp, r_field.get_numeric_grid(0), f_grid);
    interpweights(itw, gp);
    interp(surface_scalar_reflectivity, itw, r_f, gp);
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_scalar_reflectivityFromSurface_rmatrix(
    Vector& surface_scalar_reflectivity,
    const Tensor4& surface_rmatrix,
    const Verbosity&) {
  const Index nf = surface_rmatrix.npages();
  const Index nlos = surface_rmatrix.nbooks();
 
  surface_scalar_reflectivity.resize(nf);
  surface_scalar_reflectivity = 0;
 
  for (Index i = 0; i < nf; i++) {
    for (Index l = 0; l < nlos; l++) {
      surface_scalar_reflectivity[i] += surface_rmatrix(l, i, 0, 0);
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void InterpSurfaceTypeMask(Index& surface_type,
                           const Index& atmosphere_dim,
                           const Vector& lat_grid,
                           const Vector& lat_true,
                           const Vector& lon_true,
                           const Vector& rtp_pos,
                           const GriddedField2& surface_type_mask,
                           const Verbosity&) {
  // Set expected order of grids
  Index gfield_latID = 0;
  Index gfield_lonID = 1;
 
  // Basic checks and sizes
  chk_if_in_range("atmosphere_dim", atmosphere_dim, 1, 3);
  chk_latlon_true(atmosphere_dim, lat_grid, lat_true, lon_true);
  chk_rte_pos(atmosphere_dim, rtp_pos);
  surface_type_mask.checksize_strict();
  //
  chk_griddedfield_gridname(surface_type_mask, gfield_latID, "Latitude");
  chk_griddedfield_gridname(surface_type_mask, gfield_lonID, "Longitude");
  //
  const Index nlat = surface_type_mask.data.nrows();
  const Index nlon = surface_type_mask.data.ncols();
  //
  if (nlat < 2 || nlon < 2) {
    ostringstream os;
    os << "The data in *surface_type_mask* must span a geographical "
       << "region. Accordingly,\nthe latitude and longitude grids must "
       << "both have a length >= 2.";
    throw runtime_error(os.str());
  }
 
  const Vector& GFlat = surface_type_mask.get_numeric_grid(gfield_latID);
  const Vector& GFlon = surface_type_mask.get_numeric_grid(gfield_lonID);
 
  // Determine true geographical position
  Vector lat(1), lon(1);
  pos2true_latlon(
      lat[0], lon[0], atmosphere_dim, lat_grid, lat_true, lon_true, rtp_pos);
 
  // Ensure correct coverage of lon grid
  Vector lon_shifted;
  lon_shiftgrid(lon_shifted, GFlon, lon[0]);
 
  // Check if lat/lon we need are actually covered
  chk_if_in_range("rtp_pos.lat", lat[0], GFlat[0], GFlat[nlat - 1]);
  chk_if_in_range("rtp_pos.lon", lon[0], lon_shifted[0], lon_shifted[nlon - 1]);
 
  // Grid positions
  GridPos gp_lat, gp_lon;
  gridpos(gp_lat, GFlat, lat[0]);
  gridpos(gp_lon, lon_shifted, lon[0]);
  
  // Extract closest point
  Index ilat, ilon;
  if (gp_lat.fd[0] < 0.5) {
    ilat = gp_lat.idx;
  } else {
    ilat = gp_lat.idx + 1;
  }
  if (gp_lon.fd[0] < 0.5) {
    ilon = gp_lon.idx;
  } else {
    ilon = gp_lon.idx + 1;
  }
  surface_type = (Index)round(surface_type_mask.data(ilat, ilon));
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_rtpropFromTypesAverage(
       Workspace& ws,
       Vector& surface_type_mix,
       Numeric& surface_skin_t,
       Matrix& surface_los,
       Tensor4& surface_rmatrix,
       Matrix& surface_emission,
       const Vector& f_grid,
       const Index& stokes_dim,
       const Index& atmosphere_dim,
       const Vector& lat_grid,
       const Vector& lon_grid,
       const Vector& lat_true,
       const Vector& lon_true,
       const Vector& rtp_pos,
       const Vector& rtp_los,
       const Vector& refellipsoid,
       const GriddedField2& surface_type_mask,
       const ArrayOfAgenda& surface_rtprop_agenda_array,
       const Numeric& z_sensor,
       const Matrix& dlos,
       const Vector& dlos_weight_vector,
       const Verbosity& verbosity)
{
  ARTS_USER_ERROR_IF(atmosphere_dim != 3, "This method only works for 3D.");
 
  // Determine satellite sensor_pos and sensor_los
  Vector sat_pos = rtp_pos;
  Vector sat_los = rtp_los;
  rte_pos_losBackwardToAltitude(sat_pos,
                                sat_los,
                                atmosphere_dim,
                                lat_grid,
                                lon_grid,
                                refellipsoid,
                                z_sensor,
                                0,
                                verbosity);
 
  // Some sizes
  const Index nf = f_grid.nelem();
  const Index ntypes = surface_rtprop_agenda_array.nelem();
  const Index nlos = dlos.nrows();
 
  // Find ground sample positions
  Matrix ground_pos, ground_los, sensor_pos(nlos, 3), sensor_los;
  //
  sensor_pos(joker, 0) = sat_pos[0];
  sensor_pos(joker, 1) = sat_pos[1];
  sensor_pos(joker, 2) = sat_pos[2];
  losAddLosAndDlos(sensor_los, sat_los, dlos, verbosity);
  //
  IntersectionGeometricalWithAltitude(ground_pos,
                                      ground_los,
                                      sensor_pos,
                                      sensor_los,
                                      refellipsoid,
                                      lat_grid,
                                      lon_grid,
                                      rtp_pos[0],
                                      verbosity);
  
  // Prepare output variables
  surface_type_mix.resize(ntypes);
  surface_type_mix = 0.;
  surface_skin_t = 0.;
  surface_los.resize(1,2);
  surface_los = 0.;
  surface_rmatrix.resize(1, nf, stokes_dim, stokes_dim);
  surface_rmatrix = 0.;
  surface_emission.resize(nf, stokes_dim);
  surface_emission = 0.;
 
  // Help variables
  const Numeric weight_sum = sum(dlos_weight_vector);
  Numeric tmp_skin_t;
  Vector tmp_type_mix;
  Matrix tmp_emission, tmp_los;
  Tensor4 tmp_rmatrix;
  
  // Loop los-es to sample
  for (Index i=0; i<nlos; ++i) {
    surface_rtpropFromTypesNearest(ws,
                                   tmp_type_mix,
                                   tmp_skin_t,
                                   tmp_los,
                                   tmp_rmatrix,
                                   tmp_emission,
                                   f_grid,
                                   atmosphere_dim,
                                   lat_grid,
                                   lat_true,
                                   lon_true,
                                   Vector{ground_pos(i, joker)},
                                   Vector{ground_los(i, joker)},
                                   surface_type_mask,
                                   surface_rtprop_agenda_array,
                                   verbosity);
    ARTS_USER_ERROR_IF(tmp_los.nrows() != 1,
                       "This method requires that all surface types "
                       "returns a *surface_los* with one row.");
 
    // Sum up
    const Numeric weight = dlos_weight_vector[i] / weight_sum;
    tmp_type_mix *= weight;
    surface_type_mix += tmp_type_mix;
    surface_skin_t += weight * tmp_skin_t;
    tmp_los *= weight;
    surface_los += tmp_los;
    tmp_rmatrix *= weight;
    surface_rmatrix += tmp_rmatrix;
    tmp_emission *= weight;
    surface_emission += tmp_emission;
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_rtpropFromTypesManual(Workspace& ws,
                                   Vector& surface_type_mix,
                                   Numeric& surface_skin_t,
                                   Matrix& surface_los,
                                   Tensor4& surface_rmatrix,
                                   Matrix& surface_emission,
                                   const Vector& f_grid,
                                   const Vector& rtp_pos,
                                   const Vector& rtp_los,
                                   const ArrayOfAgenda& surface_rtprop_agenda_array,
                                   const Index& surface_type,
                                   const Verbosity&)
{
  ARTS_USER_ERROR_IF(surface_type < 0 or
     surface_type >= surface_rtprop_agenda_array.nelem(),
     "Provided surface type index invalid (<0 or too high w.r.t. "
     "length of *surface_rtprop_agenda_array*).");
  
  surface_type_mix.resize(surface_rtprop_agenda_array.nelem());
  surface_type_mix = 0.0;
  surface_type_mix[surface_type] = 1.0;
 
  surface_rtprop_agenda_arrayExecute(ws,
                                     surface_skin_t,
                                     surface_emission,
                                     surface_los,
                                     surface_rmatrix,
                                     surface_type,
                                     f_grid,
                                     rtp_pos,
                                     rtp_los,
                                     surface_rtprop_agenda_array);
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_rtpropFromTypesNearest(Workspace& ws,
                                    Vector& surface_type_mix,
                                    Numeric& surface_skin_t,
                                    Matrix& surface_los,
                                    Tensor4& surface_rmatrix,
                                    Matrix& surface_emission,
                                    const Vector& f_grid,
                                    const Index& atmosphere_dim,
                                    const Vector& lat_grid,
                                    const Vector& lat_true,
                                    const Vector& lon_true,
                                    const Vector& rtp_pos,
                                    const Vector& rtp_los,
                                    const GriddedField2& surface_type_mask,
                                    const ArrayOfAgenda& surface_rtprop_agenda_array,
                                    const Verbosity& verbosity)
{
  Index surface_type;
  InterpSurfaceTypeMask(surface_type,
                        atmosphere_dim,
                        lat_grid,
                        lat_true,
                        lon_true,
                        rtp_pos,
                        surface_type_mask,
                        verbosity);
  ARTS_USER_ERROR_IF(surface_type < 0 or
     surface_type >= surface_rtprop_agenda_array.nelem(),
     "Interpolation gave invalid surface type index (<0 or too "
     "high w.f.t. length of *surface_rtprop_agenda_array*).");
 
  surface_type_mix.resize(surface_rtprop_agenda_array.nelem());
  surface_type_mix = 0.0;
  surface_type_mix[surface_type] = 1.0;
 
  surface_rtprop_agenda_arrayExecute(ws,
                                     surface_skin_t,
                                     surface_emission,
                                     surface_los,
                                     surface_rmatrix,
                                     surface_type,
                                     f_grid,
                                     rtp_pos,
                                     rtp_los,
                                     surface_rtprop_agenda_array);
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void surface_rtpropInterpFreq(Vector& f_grid,
                              Tensor4& surface_rmatrix,
                              Matrix& surface_emission,
                              const Vector& f_new,
                              const Verbosity&) {
  const Index nf = f_grid.nelem();
  const Index ns = surface_emission.ncols();
  const Index nlos = surface_rmatrix.nbooks();
  const Index nnew = f_new.nelem();
 
  // Checks
  ARTS_USER_ERROR_IF(surface_emission.nrows() not_eq nf,
     "Different number of frequencies in *f_grid* and *surface_emission*.");
  ARTS_USER_ERROR_IF(surface_rmatrix.npages() not_eq nf,
     "Different number of frequencies in *f_grid* and *surface_rmatrix*.");
  ARTS_USER_ERROR_IF(surface_rmatrix.ncols() not_eq ns,
     "Different number of Stokes elements in *surface_emission* and *surface_rmatrix*.");
 
  // Set up interpolation
  chk_interpolation_grids("Frequency interpolation", f_grid, f_new);
  ArrayOfGridPos gp(nnew);
  Matrix itw(nnew, 2);
  gridpos(gp, f_grid, f_new);
  interpweights(itw, gp);
 
  // Interpolate
  Tensor4 rmatrix = surface_rmatrix;
  Matrix emission = surface_emission;
  surface_rmatrix.resize(nlos, nnew, ns, ns);
  surface_emission.resize(nnew, ns);
  //
  for (Index is = 0; is < ns; ++is) {
    interp(surface_emission(joker, is), itw, emission(joker, is), gp);
    for (Index il = 0; il < nlos; ++il) {
      for (Index is2 = 0; is2 < ns; ++is2) {
        interp(surface_rmatrix(il, joker, is, is2),
               itw,
               rmatrix(il, joker, is, is2),
               gp);
      }
    }
  }
  f_grid = f_new;
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void SurfaceBlackbody(Matrix& surface_los,
                      Tensor4& surface_rmatrix,
                      ArrayOfTensor4& dsurface_rmatrix_dx,
                      Matrix& surface_emission,
                      ArrayOfMatrix& dsurface_emission_dx,
                      const Index& stokes_dim,
                      const Index& atmosphere_dim,
                      const Vector& lat_grid,
                      const Vector& lon_grid,
                      const Vector& f_grid,
                      const Vector& rtp_pos,
                      const Vector& rtp_los,
                      const Tensor3& surface_props_data,
                      const ArrayOfString& surface_props_names,
                      const ArrayOfString& dsurface_names,
                      const Index& jacobian_do,
                      const Verbosity& verbosity) {
  // Check surface_data
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  // Interplation grid positions and weights
  ArrayOfGridPos gp_lat(1), gp_lon(1);
  Matrix itw;
  rte_pos2gridpos(
      gp_lat[0], gp_lon[0], atmosphere_dim, lat_grid, lon_grid, rtp_pos);
  interp_atmsurface_gp2itw(itw, atmosphere_dim, gp_lat, gp_lon);
 
  // Skin temperature
  Vector skin_t(1);
  surface_props_interp(skin_t,
                       "Skin temperature",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  surfaceBlackbody(surface_los,
                   surface_rmatrix,
                   surface_emission,
                   atmosphere_dim,
                   f_grid,
                   stokes_dim,
                   rtp_pos,
                   rtp_los,
                   skin_t[0],
                   verbosity);
 
  surface_rmatrix.resize(1, f_grid.nelem(), stokes_dim, stokes_dim);
  surface_rmatrix = 0.0;
 
  // Jacobian part
  if (jacobian_do) {
    dsurface_check(surface_props_names,
                   dsurface_names,
                   dsurface_rmatrix_dx,
                   dsurface_emission_dx);
 
    Index irq;
 
    // Skin temperature
    irq = find_first(dsurface_names, String("Skin temperature"));
    if (irq >= 0) {
      Matrix dbdt(f_grid.nelem(), 1);
      dplanck_dt(dbdt(joker, 0), f_grid, skin_t[0]);
      dsurface_emission_dx[irq] = dbdt;
      dsurface_rmatrix_dx[irq].resize(surface_rmatrix.nbooks(),
                                      surface_rmatrix.npages(),
                                      surface_rmatrix.nrows(),
                                      surface_rmatrix.ncols());
      dsurface_rmatrix_dx[irq] = 0;
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void SurfaceDummy(ArrayOfTensor4& dsurface_rmatrix_dx,
                  ArrayOfMatrix& dsurface_emission_dx,
                  const Index& atmosphere_dim,
                  const Vector& lat_grid,
                  const Vector& lon_grid,
                  const Tensor3& surface_props_data,
                  const ArrayOfString& surface_props_names,
                  const ArrayOfString& dsurface_names,
                  const Index& jacobian_do,
                  const Verbosity&) {
  if (surface_props_names.nelem())
    throw runtime_error(
        "When calling this method, *surface_props_names* should be empty.");
 
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  if (jacobian_do) {
    dsurface_check(surface_props_names,
                   dsurface_names,
                   dsurface_rmatrix_dx,
                   dsurface_emission_dx);
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void SurfaceFastem(Matrix& surface_los,
                   Tensor4& surface_rmatrix,
                   ArrayOfTensor4& dsurface_rmatrix_dx,
                   Matrix& surface_emission,
                   ArrayOfMatrix& dsurface_emission_dx,
                   const Index& stokes_dim,
                   const Index& atmosphere_dim,
                   const Vector& lat_grid,
                   const Vector& lon_grid,
                   const Vector& f_grid,
                   const Vector& rtp_pos,
                   const Vector& rtp_los,
                   const Tensor3& surface_props_data,
                   const ArrayOfString& surface_props_names,
                   const ArrayOfString& dsurface_names,
                   const Index& jacobian_do,
                   const Vector& transmittance,
                   const Index& fastem_version,
                   const Verbosity& verbosity) {
  // Check surface_data
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  // Interplation grid positions and weights
  ArrayOfGridPos gp_lat(1), gp_lon(1);
  Matrix itw;
  rte_pos2gridpos(
      gp_lat[0], gp_lon[0], atmosphere_dim, lat_grid, lon_grid, rtp_pos);
  interp_atmsurface_gp2itw(itw, atmosphere_dim, gp_lat, gp_lon);
 
  // Skin temperature
  Vector skin_t(1);
  surface_props_interp(skin_t,
                       "Water skin temperature",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Wind speed
  Vector wind_speed(1);
  surface_props_interp(wind_speed,
                       "Wind speed",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Wind direction
  Vector wind_direction(1);
  surface_props_interp(wind_direction,
                       "Wind direction",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Salinity
  Vector salinity(1);
  surface_props_interp(salinity,
                       "Salinity",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Call FASTEM
  surfaceFastem(surface_los,
                surface_rmatrix,
                surface_emission,
                atmosphere_dim,
                stokes_dim,
                f_grid,
                rtp_pos,
                rtp_los,
                skin_t[0],
                salinity[0],
                wind_speed[0],
                wind_direction[0],
                transmittance,
                fastem_version,
                verbosity);
 
  // Jacobian part
  if (jacobian_do) {
    dsurface_check(surface_props_names,
                   dsurface_names,
                   dsurface_rmatrix_dx,
                   dsurface_emission_dx);
 
    Index irq;
 
    // Skin temperature
    irq = find_first(dsurface_names, String("Water skin temperature"));
    if (irq >= 0) {
      const Numeric dd = 0.1;
      Matrix surface_los2;
      surfaceFastem(surface_los2,
                    dsurface_rmatrix_dx[irq],
                    dsurface_emission_dx[irq],
                    atmosphere_dim,
                    stokes_dim,
                    f_grid,
                    rtp_pos,
                    rtp_los,
                    skin_t[0] + dd,
                    salinity[0],
                    wind_speed[0],
                    wind_direction[0],
                    transmittance,
                    fastem_version,
                    verbosity);
      //
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
 
    // Wind speed
    irq = find_first(dsurface_names, String("Wind speed"));
    if (irq >= 0) {
      const Numeric dd = 0.1;
      Matrix surface_los2;
      surfaceFastem(surface_los2,
                    dsurface_rmatrix_dx[irq],
                    dsurface_emission_dx[irq],
                    atmosphere_dim,
                    stokes_dim,
                    f_grid,
                    rtp_pos,
                    rtp_los,
                    skin_t[0],
                    salinity[0],
                    wind_speed[0] + dd,
                    wind_direction[0],
                    transmittance,
                    fastem_version,
                    verbosity);
      //
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
 
    // Wind direction
    irq = find_first(dsurface_names, String("Wind direction"));
    if (irq >= 0) {
      const Numeric dd = 1;
      Matrix surface_los2;
      surfaceFastem(surface_los2,
                    dsurface_rmatrix_dx[irq],
                    dsurface_emission_dx[irq],
                    atmosphere_dim,
                    stokes_dim,
                    f_grid,
                    rtp_pos,
                    rtp_los,
                    skin_t[0],
                    salinity[0],
                    wind_speed[0],
                    wind_direction[0] + dd,
                    transmittance,
                    fastem_version,
                    verbosity);
      //
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
 
    // Salinity
    irq = find_first(dsurface_names, String("Salinity"));
    if (irq >= 0) {
      const Numeric dd = 0.0005;
      Matrix surface_los2;
      surfaceFastem(surface_los2,
                    dsurface_rmatrix_dx[irq],
                    dsurface_emission_dx[irq],
                    atmosphere_dim,
                    stokes_dim,
                    f_grid,
                    rtp_pos,
                    rtp_los,
                    skin_t[0],
                    salinity[0] + dd,
                    wind_speed[0],
                    wind_direction[0],
                    transmittance,
                    fastem_version,
                    verbosity);
      //
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
  }
}
 
 
/* Workspace method: Doxygen documentation will be auto-generated */
void SurfaceFlatScalarReflectivity(Matrix& surface_los,
                                   Tensor4& surface_rmatrix,
                                   ArrayOfTensor4& dsurface_rmatrix_dx,
                                   Matrix& surface_emission,
                                   ArrayOfMatrix& dsurface_emission_dx,
                                   const Index& stokes_dim,
                                   const Index& atmosphere_dim,
                                   const Vector& lat_grid,
                                   const Vector& lon_grid,
                                   const Vector& f_grid,
                                   const Vector& rtp_pos,
                                   const Vector& rtp_los,
                                   const Vector& specular_los,
                                   const Tensor3& surface_props_data,
                                   const ArrayOfString& surface_props_names,
                                   const ArrayOfString& dsurface_names,
                                   const Index& jacobian_do,
                                   const Vector& f_reflectivities,
                                   const Verbosity& verbosity) {
  // Check surface_data
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  // Check of GINs
  chk_if_increasing("GIN *f_reflectivities*", f_reflectivities);
 
  // Sizes
  const Index nr = f_reflectivities.nelem();
  const Index nf = f_grid.nelem();
 
  // Interplation grid positions and weights
  ArrayOfGridPos gp_lat(1), gp_lon(1);
  Matrix itw;
  rte_pos2gridpos(
      gp_lat[0], gp_lon[0], atmosphere_dim, lat_grid, lon_grid, rtp_pos);
  interp_atmsurface_gp2itw(itw, atmosphere_dim, gp_lat, gp_lon);
 
  // Skin temperature
  Vector surface_skin_t(1);
  surface_props_interp(surface_skin_t,
                       "Skin temperature",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Reflectivities
  Vector reflectivities(nr);
  //
  for (Index i=0; i<nr; i++) {
    Vector rv(1);
    ostringstream sstr;
    sstr << "Scalar reflectivity " << i;
    surface_props_interp(rv,
                         sstr.str(),
                         atmosphere_dim,
                         gp_lat,
                         gp_lon,
                         itw,
                         surface_props_data,
                         surface_props_names);
    reflectivities[i] = rv[0];
  }
 
  // Create surface_scalar_reflectivity
  Vector surface_scalar_reflectivity(nf);
  ArrayOfGridPos gp(nf);
  if (nr==1) {
    gp4length1grid(gp);
  } else {
    gridpos(gp, f_reflectivities, f_grid, 1e99);
    jacobian_type_extrapol(gp);
  }
  Matrix itw2(nf, 2);
  interpweights(itw2, gp);
  interp( surface_scalar_reflectivity, itw2, reflectivities, gp);
 
  // Call non-Jacobian method
  surfaceFlatScalarReflectivity(surface_los,
                                surface_rmatrix,
                                surface_emission,
                                f_grid,
                                stokes_dim,
                                atmosphere_dim,
                                rtp_pos,
                                rtp_los,
                                specular_los,
                                surface_skin_t[0],
                                surface_scalar_reflectivity,
                                verbosity);
  
  // Jacobian part
  if (jacobian_do) {
    dsurface_check(surface_props_names,
                   dsurface_names,
                   dsurface_rmatrix_dx,
                   dsurface_emission_dx);
 
    Index irq;
 
    // Skin temperature
    irq = find_first(dsurface_names, String("Skin temperature"));
    if (irq >= 0) {
      const Numeric dd = 0.1;
      Matrix surface_los2;
      surfaceFlatScalarReflectivity(surface_los2,
                                    dsurface_rmatrix_dx[irq],
                                    dsurface_emission_dx[irq],
                                    f_grid,
                                    stokes_dim,
                                    atmosphere_dim,
                                    rtp_pos,
                                    rtp_los,
                                    specular_los,
                                    surface_skin_t[0]+dd,
                                    surface_scalar_reflectivity,
                                    verbosity);
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
 
    // Reflectivities
    for (Index i=0; i<nr; i++) {
      ostringstream sstr;
      sstr << "Scalar reflectivity " << i;
      irq = find_first(dsurface_names, String(sstr.str()));
      if (irq >= 0) {
        const Numeric dd = 1e-4;
        Vector rpert = reflectivities;
        rpert[i] += dd;
        interp( surface_scalar_reflectivity, itw2, rpert, gp);
        //
        Matrix surface_los2;
        surfaceFlatScalarReflectivity(surface_los2,
                                      dsurface_rmatrix_dx[irq],
                                      dsurface_emission_dx[irq],
                                      f_grid,
                                      stokes_dim,
                                      atmosphere_dim,
                                      rtp_pos,
                                      rtp_los,
                                      specular_los,
                                      surface_skin_t[0],
                                      surface_scalar_reflectivity,
                                      verbosity);
        dsurface_rmatrix_dx[irq] -= surface_rmatrix;
        dsurface_rmatrix_dx[irq] /= dd;
        dsurface_emission_dx[irq] -= surface_emission;
        dsurface_emission_dx[irq] /= dd;
      }
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void SurfaceTessem(Matrix& surface_los,
                   Tensor4& surface_rmatrix,
                   ArrayOfTensor4& dsurface_rmatrix_dx,
                   Matrix& surface_emission,
                   ArrayOfMatrix& dsurface_emission_dx,
                   const Index& stokes_dim,
                   const Index& atmosphere_dim,
                   const Vector& lat_grid,
                   const Vector& lon_grid,
                   const Vector& f_grid,
                   const Vector& rtp_pos,
                   const Vector& rtp_los,
                   const TessemNN& net_h,
                   const TessemNN& net_v,
                   const Tensor3& surface_props_data,
                   const ArrayOfString& surface_props_names,
                   const ArrayOfString& dsurface_names,
                   const Index& jacobian_do,
                   const Verbosity& verbosity) {
  // Check surface_data
  surface_props_check(atmosphere_dim,
                      lat_grid,
                      lon_grid,
                      surface_props_data,
                      surface_props_names);
 
  // Interplation grid positions and weights
  ArrayOfGridPos gp_lat(1), gp_lon(1);
  Matrix itw;
  rte_pos2gridpos(
      gp_lat[0], gp_lon[0], atmosphere_dim, lat_grid, lon_grid, rtp_pos);
  interp_atmsurface_gp2itw(itw, atmosphere_dim, gp_lat, gp_lon);
 
  // Skin temperature
  Vector skin_t(1);
  surface_props_interp(skin_t,
                       "Water skin temperature",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Wind speed
  Vector wind_speed(1);
  surface_props_interp(wind_speed,
                       "Wind speed",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Salinity
  Vector salinity(1);
  surface_props_interp(salinity,
                       "Salinity",
                       atmosphere_dim,
                       gp_lat,
                       gp_lon,
                       itw,
                       surface_props_data,
                       surface_props_names);
 
  // Call TESSEM
  surfaceTessem(surface_los,
                surface_rmatrix,
                surface_emission,
                atmosphere_dim,
                stokes_dim,
                f_grid,
                rtp_pos,
                rtp_los,
                skin_t[0],
                net_h,
                net_v,
                salinity[0],
                wind_speed[0],
                verbosity);
 
  // Jacobian part
  if (jacobian_do) {
    dsurface_check(surface_props_names,
                   dsurface_names,
                   dsurface_rmatrix_dx,
                   dsurface_emission_dx);
 
    Index irq;
 
    // Skin temperature
    irq = find_first(dsurface_names, String("Water skin temperature"));
    if (irq >= 0) {
      const Numeric dd = 0.1;
      Matrix surface_los2;
      surfaceTessem(surface_los2,
                    dsurface_rmatrix_dx[irq],
                    dsurface_emission_dx[irq],
                    atmosphere_dim,
                    stokes_dim,
                    f_grid,
                    rtp_pos,
                    rtp_los,
                    skin_t[0] + dd,
                    net_h,
                    net_v,
                    salinity[0],
                    wind_speed[0],
                    verbosity);
      //
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
 
    // Wind speed
    irq = find_first(dsurface_names, String("Wind speed"));
    if (irq >= 0) {
      const Numeric dd = 0.1;
      Matrix surface_los2;
      surfaceTessem(surface_los2,
                    dsurface_rmatrix_dx[irq],
                    dsurface_emission_dx[irq],
                    atmosphere_dim,
                    stokes_dim,
                    f_grid,
                    rtp_pos,
                    rtp_los,
                    skin_t[0],
                    net_h,
                    net_v,
                    salinity[0],
                    wind_speed[0] + dd,
                    verbosity);
      //
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
 
    // Salinity
    irq = find_first(dsurface_names, String("Salinity"));
    if (irq >= 0) {
      const Numeric dd = 0.0005;
      Matrix surface_los2;
      surfaceTessem(surface_los2,
                    dsurface_rmatrix_dx[irq],
                    dsurface_emission_dx[irq],
                    atmosphere_dim,
                    stokes_dim,
                    f_grid,
                    rtp_pos,
                    rtp_los,
                    skin_t[0],
                    net_h,
                    net_v,
                    salinity[0] + dd,
                    wind_speed[0],
                    verbosity);
      //
      dsurface_rmatrix_dx[irq] -= surface_rmatrix;
      dsurface_rmatrix_dx[irq] /= dd;
      dsurface_emission_dx[irq] -= surface_emission;
      dsurface_emission_dx[irq] /= dd;
    }
  }
}
 
/* Workspace method: Doxygen documentation will be auto-generated */
void transmittanceFromIy_aux(Vector& transmittance,
                             const ArrayOfString& iy_aux_vars,
                             const ArrayOfMatrix& iy_aux,
                             const Verbosity&) {
  Index ihit = -1;
 
  for (Index i = 0; i < iy_aux_vars.nelem(); i++) {
    if (iy_aux_vars[i] == "Optical depth") {
      ihit = i;
      break;
    }
  }
 
  if (ihit < 0)
    throw runtime_error("No element in *iy_aux* holds optical depths.");
 
  const Index n = iy_aux[ihit].nrows();
 
  transmittance.resize(n);
 
  for (Index i = 0; i < n; i++) {
    transmittance[i] = exp(-iy_aux[ihit](i, 0));
  }
}