# ARTS built-in documentation server

## Workspace Method abs_lookupCalc

### Description

Creates a gas absorption lookup table. The lookup table stores absorption cross-sections as a function of pressure. Additionally, absorption can be stored as a function of temperature for temperature perturbations from a reference profile. Additionally, absorption can be stored as a function of water vapor VMR perturbations from a reference profile. The variable abs_nls specifies, for which species water vapor perturbations should be generated. Note, that the absorbing gas can be any gas, but the perturbing gas is always H2O.

**Authors: **Stefan Buehler

### Synopsis

abs_lookupCalc( | abs_lookup, abs_lookup_is_adapted, abs_species, abs_nls, f_grid, abs_p, abs_vmrs, abs_t, abs_t_pert, abs_nls_pert, propmat_clearsky_agenda, lowest_vmr ) |

### Variables

OUT | abs_lookup | (GasAbsLookup) | An absorption lookup table. |

OUT | abs_lookup_is_adapted | (Index) | Flag to indicate whether abs_lookupAdapt has already been called. |

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

IN | abs_nls | (ArrayOfArrayOfSpeciesTag) | Nonlinear species for absorption lookup table generation. |

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

IN | abs_p | (Vector) | List of pressures to be used for the calculation of absorption coefficients. |

IN | abs_vmrs | (Matrix) | The VMRs (unit: absolute number) on the abs_p grid. |

IN | abs_t | (Vector) | List of temperatures to be used for the calculation of absorption coefficients. |

IN | abs_t_pert | (Vector) | Temperature perturbations for the absorption lookup table. |

IN | abs_nls_pert | (Vector) | Fractional perturbations for the nonlinear species in the absorption lookup table. |

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

GIN | lowest_vmr | (Numeric, Default: 1e-9) | Lowest possible VMR to compute absorption at |