Making/Using LUT files, simple case
RFM Examples		09FEB24

Description

• RFM Use of Look-Up Tables of Absorption Coefficient

Step 1: Create the LUT

*FLG section

TAB flag: switches RFM into LUT-generation mode

*SPC section

Sets the wavenumber axis for the LUT file

*ATM section

An atmospheric profile containing at least pressure, temperature and target molecule is always required in order to establish profiles of T and the target molecule (CO here) included in the LUT file format, but in this example the embedded profiles have no effect.

*DIM section

Sets the pressure and temperature axes for the LUT file

• 31 points equally spaced in log(pressure) (set by '-' sign in -31) from 1000 hPa to 0.01 hPa, ie 6 points for every factor 10 change in pressure.
• 14 points equally spaced in temperature from 180K–310K, ie 10K intervals

Driver Table

*HDR 09FEB24 RFM Example: Create CO LUT *FLG TAB *SPC 2150 2155 0.0005 *GAS CO *ATM ../atm/usa.atm *DIM -31 1000 0.01 14 180 310 *HIT ../hit/hitran_2016.bin *END

Output Files

• tab_co.asc
• rfm.log

Step 2: Using the LUT

*FLG section

LUT flag: using LUTs for (some) molecular absorption data

*SPC section

The spectral range here need not match the LUT, but must be completely within it, otherwise the RFM reverts to a line-by-line calculation (or, here, would fail since no HITRAN data is supplied) The resolution need not match the LUT.

*GAS section

Although just CO is included here, other molecules can also be added as long as the spectroscopic data is supplied, eg via other LUT files or HITRAN data (*HIT section as above)

*LUT section

LUT file(s) to be used

Driver Table

*HDR 09FEB24 RFM Example: Use CO LUT *FLG RAD LUT *SPC 2150 2155 0.0005 *GAS CO *ATM ../atm/usa.atm *TAN 10.0 *LUT tab_co.asc *END

Output Spectrum

• [plot.py]

Orange line shows around 1% difference compared with line-by-line calculation, which would be reduced with finer spacing for p,T axes.

• RFM Examples