# ARTS built-in documentation server

## Workspace Method SurfaceFlatScalarReflectivity

### Description

Piecewise linear scalar surface reflectivity. This method is similar to surfaceFlatScalarReflectivity but the reflectivities are specified differently and Jacobian calculations are supported. See SurfaceFastem for general remarks about methods of SurfaceSomething type. The method works with scalar reflectivies, i.e. it is assumed that the reflection at vertical and horizontal polarisation is identical. The scalar reflectivity is given at a number of frequencies, specified by the GIN ``f_reflectivities``. The reflectivity at the first frequency is denoted as "Scalar reflectivity 0" etc. Between the frequencies in ``f_reflectivities``, the reflectivity is treated to vary linearly. The reflectivity is assumed to be constant outside of ``f_reflectivities``, and the end points in ``f_reflectivities`` can be both inside and outside of the range of f_grid. Setting ``f_reflectivities`` to have a single value, implies that the reflectivity is constant over f_grid. For this method, surface_props_data must contain these data: "Skin temperature" "Scalar reflectivity 0" "Scalar reflectivity 1" ... "Scalar reflectivity N" where N is the length of ``f_reflectivities``-1.

**Authors: **Patrick Eriksson

### Synopsis

SurfaceFlatScalarReflectivity( | surface_los, surface_rmatrix, dsurface_rmatrix_dx, surface_emission, dsurface_emission_dx, stokes_dim, atmosphere_dim, lat_grid, lon_grid, f_grid, rtp_pos, rtp_los, specular_los, surface_props_data, surface_props_names, dsurface_names, jacobian_do, f_reflectivities ) |

### Variables

OUT | surface_los | (Matrix) | Downwelling radiation directions to consider in surface reflection. |

OUT | surface_rmatrix | (Tensor4) | The reflection coefficients for the directions given by surface_los to the direction of interest. |

OUT+IN | dsurface_rmatrix_dx | (ArrayOfTensor4) | The derivative of surface_rmatrix with respect to quantities listed in dsurface_names. |

OUT | surface_emission | (Matrix) | The emission from the surface. |

OUT+IN | dsurface_emission_dx | (ArrayOfMatrix) | The derivative of surface_emission with respect to quantities listed in dsurface_names. |

IN | stokes_dim | (Index) | The dimensionality of the Stokes vector (1-4). |

IN | atmosphere_dim | (Index) | The atmospheric dimensionality (1-3). |

IN | lat_grid | (Vector) | The latitude grid. |

IN | lon_grid | (Vector) | The longitude grid. |

IN | f_grid | (Vector) | The frequency grid for monochromatic pencil beam calculations. |

IN | rtp_pos | (Vector) | Position of a radiative transfer point. |

IN | rtp_los | (Vector) | Line-of-sight at a radiative transfer point. |

IN | specular_los | (Vector) | The specular direction (for reflection by a flat surface). |

IN | surface_props_data | (Tensor3) | Various surface properties. |

IN | surface_props_names | (ArrayOfString) | Name on surface properties found in surface_props_data. |

IN | dsurface_names | (ArrayOfString) | Name of surface retrieval quantities. |

IN | jacobian_do | (Index) | Flag to activate (clear-sky) Jacobian calculations. |

GIN | f_reflectivities | (Vector) | Frequency retrieval grid, see above. |