# ARTS built-in documentation server

## Workspace Method propmat_clearskyAddParticles

### Description

Calculates absorption coefficients of particles to be used in clearsky (non-cloudbox) calculations. This is a method to include particles (neglecting possible scattering components) in a clearsky calculation, i.e. without applying the cloudbox and scattering solvers. Particles are handled as absorbing species with one instance of 'particles' per scattering element considered added to abs_species. Particle absorption cross- sections at current atmospheric conditions are extracted from the single scattering data stored in scat_data, i.e., one array element per 'particles' instance in abs_species is required. Number densities are stored in vmr_field_raw or vmr_field as for all abs_species, but can be taken from (raw) pnd_field type data. Note that the absorption coefficient is applied both in the extinction term (neglecting scattering out of the line of sight) and the emission term (neglecting the scattering source term, i.e. scattering into the line of sight). Optionally, particle extinction (sum of absorption and scattering coefficient) can be used instead of absorption only. To choose this case, set the *use_abs_as_ext* flag to 0. However, be aware that this creates some unphysical emission term, hence is only suitable, where the source term is negligible anyways, e.g. for occultation simulations. A line-of-sight direction rtp_los is required as particles can exhibit directional dependent absorption properties, which is taken into account by this method. ScatElementsToabs_speciesAdd can be used to add all required settings/data for individual scattering elements at once, i.e. a 'particles' tag to abs_species, a set of single scattering data to scat_data and a number density field to vmr_field_raw (vmr_field is derived applying AtmFieldsCalc once VMRs for all abs_species have been added) is appended for each scattering element. Like all 'propmat_clearskyAdd*' methods, the method is additive, i.e., does not overwrite the propagation matrix propmat_clearsky, but adds further contributions.

**Authors: **Jana Mendrok

### Synopsis

propmat_clearskyAddParticles( | propmat_clearsky, dpropmat_clearsky_dx, stokes_dim, atmosphere_dim, f_grid, abs_species, select_abs_species, jacobian_quantities, rtp_vmr, rtp_los, rtp_temperature, scat_data, scat_data_checked, use_abs_as_ext ) |

### Variables

OUT+IN | propmat_clearsky | (PropagationMatrix) | This contains the absorption coefficients for one point in the atmosphere (one set of pressure, temperature, magnetic field, and VMR values). |

OUT+IN | dpropmat_clearsky_dx | (ArrayOfPropagationMatrix) | Partial derivative of absorption coefficients. |

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

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

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

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

IN | select_abs_species | (ArrayOfSpeciesTag) | A select species tag group from abs_species If set to empty, this selection is void. |

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

IN | rtp_vmr | (Vector) | Absorption species abundances for radiative transfer calculations. |

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

IN | rtp_temperature | (Numeric) | Temperature at a radiative transfer point. |

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

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

GIN | use_abs_as_ext | (Index, Default: 1) | A flag with value 1 or 0. If set to one, particle absorption is used in extinction and emission parts of the RT equation, and scattering out of LOS as well as into LOS is neglected. Otherwise, particle extinction (absorption+scattering) is applied in both the extinction as well as the emission part of the RT equation. That is, true extinction is applied, but emission also includes a pseudo-emission contribution from the scattering coefficient. |