*LUT Section

RFM Driver Table Sections: LUT files

20APR24
Type
Secondary Section, requires LUT Flag.

Description
Specify filenames of Absorption Coefficient Look-Up Tables.

Format
Multiple fields, any order.
FieldTypeDescription
FILLUT C200 Name of .tab File
DEFLUT C200 Default .tab Filename template (contains '*' character)
An optional 'qualifier', contained in a pair of brackets (...), may be appended (without any spaces) to FILLUT (These are used as part of the MIPAS LUT-generation procedure, and probably not much use for anything else).
QualifierTypeRangeDescription
(NDP:NDT) 2I >0 Increase the pressure,temperature axis interval by factor NDP,NDT retaining the first point and adjusting the last point if necessary
<0 As >0 with factor |NDP|, |NDT| but retaining the last point and adjusting the first point if necessary
0 Only use a single point, nearest the middle of the original axis.

Notes
  1. LUTs are the .tab file format that can be generated by the RFM itself using the TAB Flag (either ASCII or binary), but referred to as LUTs when used as input.

  2. Each look-up table listed in this section is opened and the gas and spectral range specified in the file contents are read. If the gas matches one of the absorbers specified in the *GAS section, and the spectral range either matches or completely overlaps one or more of the ranges specified in the *SPC section, then the look-up table will be used. If not, then the default is to use the normal line-by-line/.xsc calculation. An appropriate message appears in the rfm.log file.

  3. A filename template is identified by the presence of a '*' character, which is expanded to [s][g] where [s] is the spectral range label LABSPC (if any) and [g] is the molecule name eg h2o, f11 (this follows the nomenclature of filenames generated with the TAB option).

  4. The LUT is only required to overlap the output spectral range: if an ILS convolution is required then a further check is performed on whether the LUT covers the additional range required by the width of the ILS. If this is not the case then a warning message is issued but the calculation proceeds on the assumption that the absorption beyond the edges of the LUT (for that species) is negligible.

  5. The LUT is also checked for Max/Min limits on temperature and pressure. If the RFM calculation involves paths for that absorber beyond the table limits (apart from low pressures, which is assumed normal), a warning message is sent to the rfm.log file but the calculation proceeds using the value of the LUT at the closest edge (effectively assuming k(p,T) is constant beyond p,T edges of the table).

  6. Some care is required when combining H2O LUTs with the CTM flag (see notes for H2OWNG in the *GAS section). The recommendation is to create the H2O LUTs without the CTM flag and use them with the CTM flag. The RFM will then, by default, correctly handle the 25 cm-1 truncation.
Example
*LUT ! Absorbers for microwindow CH4_0001 tab_CH4_0001h2o.asc ! Specific LUTs for h2o and co2 tab_CH4_0001co2.asc tab_CH4_0001*.asc ! Any other molecules

Bugs
Bug#34 (Fixed v5.13)
Bug#33 (Fixed v5.13)