# ARTS built-in documentation server

## Workspace Method iyClearsky

### Description

Standard method for radiative transfer calculations with emission and a direct (solar, star) source . Designed to be part of iy_main_agenda. That is, only valid outside the cloudbox (no scattering). For details se the user guide. The possible choices for iy_unit are "1" : No conversion, i.e. [W/(m^2 Hz sr)] (radiance per frequency unit). "RJBT" : Conversion to Rayleigh-Jean brightness temperature. "PlanckBT" : Conversion to Planck brightness temperature. "W/(m^2 m sr)" : Conversion to [W/(m^2 m sr)] (radiance per wavelength unit). "W/(m^2 m-1 sr)": Conversion to [W/(m^2 m-1 sr)] (radiance per wavenumber unit). Expressions applied and considerations for the unit conversion of radiances are discussed in Sec. 5.7 of the ARTS-2.0 article. iy_unit is only applied if iy_agenda_call1 is 1. This means that no unit ocnversion is applied for internal iterative calls. Recognised choices for rt_integration_option are: "first order": A first order integration is applied. "second order": A second order integration is applied. "default": Another way to select the first order option. Some auxiliary radiative transfer quantities can be obtained. Auxiliary quantities are selected by iy_aux_vars and returned by iy_aux. Valid choices for auxiliary data are: "Radiative background": Index value flagging the radiative background. The following coding is used: 0=space, 1=surface and 2=cloudbox. "Optical depth": Scalar optical depth between the observation point and the end of the present propagation path. Calculated based on the (1,1)-element of the transmittance matrix (1-based indexing), i.e. only fully valid for scalar RT. "Direct radiation": Stokes vector of direct radiation. It dimensions are number of frequencies and stokes_dim. If no star is present in the line of sight, it is zero. "Radiation Background": Stokes vector of the radiation at start of the propagation path. It dimensions are number of frequencies and stokes_dim. If nothing else is stated, only the first column of iy_aux is filled, i.e. the column matching Stokes element I, while remaing columns are are filled with zeros. IMPORTANT: No jacobian calculation is supported when stars or gas scattering is included! This will be implemented in a future version.

**Authors: **Patrick Eriksson, Richard Larsson, Oliver Lemke, Manfred Brath

### Synopsis

### Variables

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

OUT | iy_aux | (ArrayOfMatrix) | Data auxiliary to iy. |

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

OUT | ppvar_p | (Vector) | Pressure along the propagation path. |

OUT | ppvar_t | (Vector) | Temperature along the propagation path. |

OUT | ppvar_nlte | (EnergyLevelMap) | Non-LTE temperatures/ratios along the propagation path. |

OUT | ppvar_vmr | (Matrix) | VMR values along the propagation path. |

OUT | ppvar_wind | (Matrix) | Winds along the propagation path. |

OUT | ppvar_mag | (Matrix) | Magnetic field along the propagation path. |

OUT | ppvar_f | (Matrix) | Doppler adjusted frequencies along the propagation path. |

OUT | ppvar_iy | (Tensor3) | iy-values along the propagation path. |

OUT | ppvar_trans_cumulat | (Tensor4) | The transmittance between the sensor and each point of the propagation path. |

OUT | ppvar_trans_partial | (Tensor4) | The transmittance between the points along the propagation path. |

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

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 | p_grid | (Vector) | The pressure grid. |

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

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

IN | z_field | (Tensor3) | The field of geometrical altitudes. |

IN | t_field | (Tensor3) | The field of atmospheric temperatures. |

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

IN | vmr_field | (Tensor4) | VMR field. |

IN | abs_species | (ArrayOfArrayOfSpeciesTag) | Tag groups for gas absorption. |

IN | wind_u_field | (Tensor3) | Zonal component of the wind field. |

IN | wind_v_field | (Tensor3) | Meridional component of the magnetic field. |

IN | wind_w_field | (Tensor3) | Vertical wind component field. |

IN | mag_u_field | (Tensor3) | Zonal component of the magnetic field. |

IN | mag_v_field | (Tensor3) | Meridional component of the magnetic field. |

IN | mag_w_field | (Tensor3) | Vertical component of the magnetic field. |

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

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

IN | ppath_lmax | (Numeric) | Maximum length between points describing propagation paths. |

IN | ppath_lraytrace | (Numeric) | Maximum length of ray tracing steps when determining propagation paths. |

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

IN | gas_scattering_do | (Index) | Flag to activate gas scattering. |

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

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

IN | iy_aux_vars | (ArrayOfString) | Selection of quantities for iy_aux and when applicable also y_aux. |

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

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

IN | ppath | (Ppath) | The propagation path for one line-of-sight. |

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

IN | stars | (ArrayOfStar) | Array of Star. |

IN | propmat_clearsky_agenda | (Agenda) | Agenda calculating the absorption coefficient matrices. |

IN | water_p_eq_agenda | (Agenda) | Agenda to calculate the saturation pressure of water. |

IN | rt_integration_option | (String) | Switch between integration approaches for radiative transfer steps. |

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

IN | iy_space_agenda | (Agenda) | Agenda providing the downwelling radiation at the top of the atmosphere. |

IN | iy_surface_agenda | (Agenda) | Agenda providing the upwelling radiation from the surface. |

IN | iy_cloudbox_agenda | (Agenda) | Agenda deriving the intensity at boundary or interior of the cloudbox. |

IN | gas_scattering_agenda | (Agenda) | Agenda calculating gas scattering extinction and phase matrix. |

IN | ppath_step_agenda | (Agenda) | Agenda calculating a propagation path step. |

IN | iy_agenda_call1 | (Index) | Flag to handle recursive calls of iy_main_agenda The agenda iy_main_agenda can be used recursively and this flag is used to tell the methods inside the agenda which is the primary call. |

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

IN | rte_alonglos_v | (Numeric) | Velocity along the line-of-sight to consider for a RT calculation. |

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