# ARTS built-in documentation server

## Workspace Method iySurfaceFlatRefractiveIndex

### Description

This method calculates upwelling radiation for a specular flat surface due to the reflection of the downgoing diffuse radiation and emission from the surface using a predefined reflectivity matrix. This method is designed to be part of iy_surface_agenda Important this method calculates only the reflection of the diffuse downward radiation. No direct incoming radiation is considered Jacobian is supported only for Skin temperature

**Authors: **Manfred Brath

### Synopsis

iySurfaceFlatRefractiveIndex( | iy, diy_dx, dsurface_rmatrix_dx, dsurface_emission_dx, iy_transmittance, iy_id, jacobian_do, stars_do, atmosphere_dim, nlte_field, cloudbox_on, stokes_dim, f_grid, lat_grid, lon_grid, z_surface, refellipsoid, rtp_pos, rtp_los, rte_pos2, iy_unit, surface_complex_refr_index, surface_props_data, surface_props_names, dsurface_names, jacobian_quantities, iy_main_agenda ) |

### Variables

OUT+IN | iy | (Matrix) | Monochromatic pencil beam radiance spectrum. |

OUT+IN | diy_dx | (ArrayOfTensor3) | Derivative of iy with respect to retrieval quantities. |

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

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

IN | iy_transmittance | (Tensor3) | Transmittance to be included in iy. |

IN | iy_id | (Index) | Identification number of iy. |

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

IN | stars_do | (Index) | Flag to activate the star(s). |

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

IN | nlte_field | (EnergyLevelMap) | The field of NLTE temperatures and/or ratios. |

IN | cloudbox_on | (Index) | Flag to activate the cloud box. |

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

IN | z_surface | (Matrix) | The surface altitude. |

IN | refellipsoid | (Vector) | Reference ellipsoid. |

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

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

IN | rte_pos2 | (Vector) | A second geographical position to define the geometry for radiative transfer calculations. |

IN | iy_unit | (String) | Selection of output unit for radiative transfer methods. |

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

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_quantities | (ArrayOfRetrievalQuantity) | The retrieval quantities in the Jacobian matrix. |

IN | iy_main_agenda | (Agenda) | Agenda calculating the single monochromatic pencil beam spectrum. |