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Workspace Method surface_reflectivityFromGriddedField6

Description

Extracts surface reflectivities from a field of such data.

This method allows to specify a field of surface reflectivity for
automatic interpolation to points of interest. The position and
direction for which the reflectivity shall be extracted are given
by rtp_pos and rtp_los. The reflectivity field is expected to
be stored as:
   GriddedField6:
      Vector "Frequency"       [N_f]
      Vector "Stokes element"  [N_s1]
      Vector "Stokes_element"  [N_s2]
      Vector "Incidence angle" [N_ia]
      Vector "Latitude"        [N_lat]
      Vector "Longitude"       [N_lon]
      Tensor6 data[N_f][N_s1][N_s2][N_ia][N_lat][N_lon]

Grids for incidence angle, latitude and longitude must have a
length of >= 2 (ie. no automatic expansion). If the frequency grid
has length 1, this is taken as that the reflectivity is constant,
following the definition of surface_scalar_reflectivity.
The data can cover higher Stokes dimensionalities than set by
stokes_dim. Data for non-used Stokes elements are just cropped.
The order between the two Stokes dimensions is the same as in
surface_reflectivity and surface_rmatrix*.

The interpolation is done in steps:
   1: Linear interpolation for lat and lon (std. extrapolation).
   2: Interpolation in incidence angle (std. extrapolation).
      If the grid has a length of >= 4, cubic interpolation is
      applied. Otherwise linear interpolation.
   3. Linear interpolation in frequency (if input data have more
      than one frequency).

Authors: Patrick Eriksson

Synopsis

surface_reflectivityFromGriddedField6(

surface_reflectivity, stokes_dim, f_grid, atmosphere_dim, lat_grid, lat_true, lon_true, rtp_pos, rtp_los, r_field )

Variables

OUT	surface_reflectivity	(Tensor3)	Surface reflectivity, for a given position and angle.
IN	stokes_dim	(Index)	The dimensionality of the Stokes vector (1-4).
IN	f_grid	(Vector)	The frequency grid for monochromatic pencil beam calculations.
IN	atmosphere_dim	(Index)	The atmospheric dimensionality (1-3).
IN	lat_grid	(Vector)	The latitude grid.
IN	lat_true	(Vector)	Latitudinal geolocation for 1D and 2D data.
IN	lon_true	(Vector)	Longitudinal geolocation for 1D and 2D data.
IN	rtp_pos	(Vector)	Position of a radiative transfer point.
IN	rtp_los	(Vector)	Line-of-sight at a radiative transfer point.
GIN	r_field	(GriddedField6)	A field of surface reflectivities