RFM Driver Table Sections

*LUT Section: Look-Up Tables

14SEP05
Type
Secondary Section - depends on LUT Flag.

Description
Specify filenames of Look-Up Tables.

Format
Multiple fields, arbitrary order. Either DEFLUT or DEFTAB may be present, but not both.
FieldTypeDescription
FILTAB C*80 Name of .tab File
FILLUT C*80 Name of .lut File
DEFTAB C*80 Default .tab Filename template (contains '*' character)
DEFLUT C*80 Default .lut Filename template (contains '*' character)
An optional `qualifier', contained in a pair of brackets (...), may be appended (without any spaces) to FILLUT and FILTAB (These are used as part of the MIPAS LUT-generation procedure, and probably not much use for anything else).
FieldQualifierTypeRangeDescription
FILLUT (NS) I >0 Use first NS Singular Vectors (up to max of all SVs)
0 Omit LUT completely
<0 Omit last |NS| Singular Vectors (down to minimum of zero SVs)
FILTAB (NP: NT) 2I >0 Increase the pressure,temperature axis interval by factor NP,NT retaining the first point and adjusting the last point if necessary
0 Only use a single point, nearest the middle of the original axis.

Notes
  1. LUT files can either be the Abs.Coeff. tables generated by the TAB flag (ASCII or Binary .tab files), or the SVD-compressed versions (.lut file, ASCII only). These are handled differently within the program (ie the former are not stored internally due to reasons of space) but the only distinction as far as the user is concerned relates to the types of qualifier that are allowed for each file.
  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 calculation. An appropriate message appears in the rfm.runlog file.
  3. A filename template is identified by the presence of a '*' character. If the template contains the string CS_ it is assumed to be a DEFLUT template for a and the '*' character is expanded as [s]_[i] (note underscore character separating fields) where [s] is the spectral range label LABSPC and [i] is the HITRAN Index of the absorber (this follows standard nomenclature of MIPAS LUTs). If there is no CS_ string it is assumed to be a DEFTAB template, and '*' is expanded as [s][g] where [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 and 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 (quite possible at low pressures, high -lnp), a warning message is sent to the rfm.runlog 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. The effect of setting the qualifier NS=0 is not quite the same as using zero singular values for the 'log' type of LUT tabulation. Using 0 SVs implies a reconstructed value of log(k)=0, hence an absorption coefficient k = 1. It is assumed that this is undesirable, so if the qualifier is used to select 0 SVs, the tabulation treated as linear ('lin') in order to force k=0 (ie as if the gas were omitted completely, which is assumed to be the intended effect). If this happens, a warning message is written in the rfm.runlog file.
  7. Some care is required when combining H2O LUTs with the CTM flag: the normal H2O continuum requires subtracting the line absorption coefficient at 25cm-1 from line centre before combining the line shape with the continuum. This is not possible if the H2O line information comes via the LUT, so an incorrect (larger) H2O line+continuum absorption results. Solutions are:
    • Include the H2O continuum into the LUT data when it is generated (and don't use the CTM flag in the subsequent RFM calculation)
    • Same, except use H2O(NOCTM) in the *GAS section, allowing the CTM flag to be used for other continua.
Example 
*LUT                   
! Absorbers for microwindow CH4_0001 
   tab_CH4_0001h2o.asc tab_CH4_0001co2.asc ! Direct LUTs for h2o and co2
   tab_CH4_0001o3.asc(2:3)    ! Direct LUT for o3 with 2*p, 3*T axis increments
   CS_CH4_0001_06.DAT(10)     ! SVD-compressed LUT for CH4 limited to 10 S.V.s
   CS_N2O_0001_n2o01a.lut(-2) ! SVD-compressed LUT for N2O reduced by 2 S.V.s
   CS_*.DAT                   ! standard SVD-compressed LUTs for other gases

Bugs
Bug#58 (Fixed v4.26)
Bug#41 (Fixed v4.22)