# ARTS built-in documentation server

## Workspace Method surfaceFlatRefractiveIndex

### Description

Creates variables to mimic specular reflection by a (flat) surface where the complex refractive index is specified. The dielectric properties of the surface are described by surface_complex_refr_index. The Fresnel equations are used to calculate amplitude reflection coefficients. The method can thus result in that the reflection properties differ between frequencies and polarisations. Local thermodynamic equilibrium is assumed, which corresponds to that the reflection and emission coefficients add up to 1.

**Authors: **Patrick Eriksson

### Synopsis

surfaceFlatRefractiveIndex( | surface_los, surface_rmatrix, surface_emission, f_grid, stokes_dim, atmosphere_dim, rtp_pos, rtp_los, specular_los, surface_skin_t, surface_complex_refr_index ) |

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

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

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

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. |

IN | surface_complex_refr_index | (GriddedField3) | Complex refractive index of the surface, at a single point. |