# ARTS built-in documentation server

## Workspace Method surfaceTelsem

### Description

Compute surface emissivities using the TELSEM 2 model. This method uses second version of the TELSEM model for calculating land surface emissivities (F. Aires et al, "A Tool to Estimate LandâSurface Emissivities at Microwave frequencies (TELSEM) for use in numerical weather prediction" Quarterly Journal of the Royal Meteorological Society, vol. 137, (656), pp. 690-699, 2011.) This methods computes land surface emissivities for a given pencil beam using a given TELSEM2 atlas. The input must satisfy the following conditions, otherwise an error is thrown: - The input frequencies (f_grid) must be within the range [5 GHz, 900 GHz] - The skin temperature (surface_skin_t) must be within the range [180 K, 360 K] A TELSEM atlas contains only suface emissivities for locations that are classified as land. By default this WSM will throw an error if the pencil beam hits the surface at a position that is not contained in the given atlas. The above behavior can be avoided by setting *d_max* to a positive value. This enables nearest neighbor interpolation, which assigns the emissivities of the nearest found cell in the atlas to the given position. In this case, an error is only thrown if the distance of the found neighbor is higher than the provided value of *d_max. You can limit the final reflectivity applied by setting *r_min* and *r_max*. To extract a land-sea mask from a given telsem atlas see the WSM telsemSurfaceTypeLandSea.

**Authors: **Simon Pfreundschuh

### Synopsis

surfaceTelsem( | surface_los, surface_rmatrix, surface_emission, atmosphere_dim, stokes_dim, f_grid, lat_grid, lat_true, lon_true, rtp_pos, rtp_los, specular_los, surface_skin_t, atlas, r_min, r_max, d_max ) |

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

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

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 | 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. |

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

IN | surface_skin_t | (Numeric) | Surface skin temperature. |

GIN | atlas | (TelsemAtlas) | The Telsem atlas to use for the emissivity calculation. |

GIN | r_min | (Numeric, Default: 0) | Minimum allowed value for reflectivity to apply. |

GIN | r_max | (Numeric, Default: 1) | Maximum allowed value for reflectivity to apply. |

GIN | d_max | (Numeric, Default: -1.0) | Maximum allowed distance in meters for nearest neighbor interpolation in meters. Set to a negative value or zero to disable interpolation. |