# ARTS built-in documentation server

## Workspace Method yRadar

### Description

Replaces yCalc for radar/lidar calculations. The output format for iy when simulating radars and lidars differs from the standard one, and yCalc can not be used for such simulations. This method works largely as yCalc, but is tailored to handle the output from iyRadarSingleScat. Note that iy_radar_agenda replaces iy_main_agenda. The method requires additional information about the sensor, regarding its recieving properties. First of all, recieved polarisation states are taken from instrument_pol_array. Note that this WSV allows to define several measured polarisations for each transmitted signal. For example, it is possible to simulate transmittance of V and measuring backsacttered V and H. Secondly, the range averaging is described by range_bins. These bins can either be specified in altitude or two-way travel time. In both case, the edges of the range bins shall be specified. All data (including auxiliary variables) are returned as the average inside the bins. If a bin is totally outside the model atmosphere, NaN is returned. The options for iy_unit_radar are: "1" : Backscatter coefficient. Unit is 1/(m*sr). At zero attenuation, this equals the scattering matrix value for the backward direction. See further AUG. "Ze" : Equivalent reflectivity. Unit is mm^6/m^3. Conversion formula is given below. "dBZe": 10*log10(Ze/Z0), where Z0 is 1 mm^6/m^3. The conversion from backscatter coefficient to Ze is: Ze = 1e18 * lambda^4 / (k2 * pi^5) * sum(sigma), where sum(sigma) = 4 * pi * b, and b is the backscatter coefficient. The reference dielectric factor can either specified directly by the argument *k2*. For example, to mimic the CloudSat data, *k2* shall be set to 0.75 (citaion needed). If *k2* is set to be negative (which is defualt), k2 is calculated as: k2 = abs( (n^2-1)/(n^2+2) )^2, where n is the refractive index of liquid water at temperature *ze_tref* and the frequency of the radar, calculated by the MPM93 parameterization. A lower limit for dBZe is applied (*dbze_min*). The main reason is to handle the fact that dBZe is not defined for Ze=0, and dBZe is set to the clip value when Ze < 10^(dbze_min/10).

**Authors: **Patrick Eriksson

### Synopsis

yRadar( | y, y_f, y_pol, y_pos, y_los, y_aux, y_geo, jacobian, atmgeom_checked, atmfields_checked, iy_unit_radar, iy_aux_vars, stokes_dim, f_grid, cloudbox_on, cloudbox_checked, sensor_pos, sensor_los, sensor_checked, jacobian_do, jacobian_quantities, iy_radar_agenda, instrument_pol_array, range_bins, ze_tref, k2, dbze_min ) |

### Variables

OUT | y | (Vector) | The measurement vector. |

OUT | y_f | (Vector) | The frequencies associated with y. |

OUT | y_pol | (ArrayOfIndex) | The polarisation states associated with y. |

OUT | y_pos | (Matrix) | The sensor positions associated with y. |

OUT | y_los | (Matrix) | The line-of-sights associated with y. |

OUT | y_aux | (ArrayOfVector) | Data auxilary to y. |

OUT | y_geo | (Matrix) | The geo-position assigned to each element of y. |

OUT | jacobian | (Matrix) | The Jacobian matrix. |

IN | atmgeom_checked | (Index) | OK-flag for the geometry of the model atmosphere. |

IN | atmfields_checked | (Index) | OK-flag for atmospheric grids and (physical) fields. |

IN | iy_unit_radar | (String) | Unit for radar simulations. |

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

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

IN | cloudbox_checked | (Index) | OK-flag for variables associated with the cloudbox. |

IN | sensor_pos | (Matrix) | The sensor position for each measurement block. |

IN | sensor_los | (Matrix) | The sensor line-of-sight (LOS) for each measurement block. |

IN | sensor_checked | (Index) | OK-flag for sensor related variables. |

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

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

IN | iy_radar_agenda | (Agenda) | Agenda calculating pointwise backscattering. |

IN | instrument_pol_array | (ArrayOfArrayOfIndex) | Multiple definition of instrument polarisation. |

IN | range_bins | (Vector) | The range bins of an active instrument. |

GIN | ze_tref | (Numeric, Default: 273.15) | Reference temperature for conversion to Ze. |

GIN | k2 | (Numeric, Default: -1) | Reference dielectric factor. |

GIN | dbze_min | (Numeric, Default: -99) | Clip value for dBZe. |