# ARTS built-in documentation server

## Workspace Method iyRadarSingleScat

### Description

Simulation of radar, restricted to single scattering. The WSM treats e.g. radar measurements of cloud and precipitation, on the condition that multiple scattering can be ignored. Beside the direct back-scattering, the two-way attenuation by gases and particles is considered. Surface scattering/clutter is ignored. The method could potentially be used for lidars, but multiple scattering poses here a must stronger constrain for the range of applications. The method shall be used with yRadar, NOT with yCalc. The ppath provided should be calculated including cloudbox interior: ppathCalc( cloudbox_on=0 ) The method returns the back-scattering for each point of ppath. Several frequencies can be treated in parallel. The size of iy is [ nf*np, stokes_dim ], where nf is the length of f_grid and np is the number of path points. The data are stored in blocks of [ np, stokes_dim ]. That is, all the results for the first frequency occupy the np first rows of iy etc. The polarisation state of the transmitted pulse is taken from iy_transmitter_agenda. If the radar transmits several polarisations at the same frequency, you need to handle this by using two frequencies in f_grid, but these can be almost identical. This method does not consider iy_unit_radar. Unit changes are instead applied in *yRadar. The output of this method matches the option "1". The extinction due to particles can be scaled (by *pext_scaling*), which could be of interest when e.g. characterising inversions or trying to compensate for ignored multiple scattering. The later is commented further for particle_bulkpropRadarOnionPeeling. For Jacobian calculations the default is to assume that the transmittance is unaffected by the retrieval quantities. This is done to save computational time, and should be a valid approximation for the single-scattering conditions. Set *trans_in_jacobian* to 1 to activate full Jacobian calculations. 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 (the last case should not occur!). Only column matching first Stokes element filled. Other columns are set to 0. "Backscattering": The unattenuated back-scattering. That is, as iy but with no attenuated applied. Here all columns are filled. By combing iy and this auxiliary variable, the total two-way attenuation can be derived. "Abs species extinction": Extinction due to abs_species at each ppath point, taken as the diagonal of the local extinction matrix. "Particle extinction": Extinction due to particles at each ppath point, taken as the diagonal of the local extinction matrix. The retunred values includes *pext_scaling*

**Authors: **Patrick Eriksson

### Synopsis

iyRadarSingleScat( | iy, iy_aux, diy_dx, ppvar_p, ppvar_t, ppvar_vmr, ppvar_wind, ppvar_mag, ppvar_pnd, ppvar_f, stokes_dim, f_grid, atmosphere_dim, p_grid, t_field, nlte_field, vmr_field, abs_species, wind_u_field, wind_v_field, wind_w_field, mag_u_field, mag_v_field, mag_w_field, cloudbox_on, cloudbox_limits, pnd_field, dpnd_field_dx, scat_species, scat_data, scat_data_checked, iy_aux_vars, jacobian_do, jacobian_quantities, ppath, propmat_clearsky_agenda, water_p_eq_agenda, iy_transmitter_agenda, rte_alonglos_v, trans_in_jacobian, pext_scaling, t_interp_order ) |

### Variables

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

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

OUT | 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_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_pnd | (Matrix) | PND values along the propagation path. |

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

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

IN | cloudbox_limits | (ArrayOfIndex) | The limits of the cloud box. |

IN | pnd_field | (Tensor4) | Particle number density field. |

IN | dpnd_field_dx | (ArrayOfTensor4) | Partial derivatives of pnd_field. |

IN | scat_species | (ArrayOfString) | Array of Strings defining the scattering species to consider. |

IN | scat_data | (ArrayOfArrayOfSingleScatteringData) | Array of single scattering data. |

IN | scat_data_checked | (Index) | OK-flag for scat_data. |

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 | 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 | iy_transmitter_agenda | (Agenda) | Agenda providing a transmitter signal. |

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

GIN | trans_in_jacobian | (Index, Default: 0) | Flag determining if change in transmittance is considered in calculation of the Jacobian or not. |

GIN | pext_scaling | (Numeric, Default: 1) | Particle extinction is scaled with this value. A value inside [0,2]. Set it to 0 if you want to remove particle extinction totally. |

GIN | t_interp_order | (Index, Default: 1) | Interpolation order of temperature for scattering data (so far only applied in phase matrix, not in extinction and absorption. |