RFM Examples

Nadir Microwave Spectra

04JUL17


Description

Nadir-viewing microwave calculation.

*FLG section specifies

NAD flag
Downward viewing through a plane parallel atmosphere;
SFC flag
Mandatory with the NAD flag, indicating that surface contributions are included. In the absence of any *SFC section in the driver table, default values are assumed, ie surface temperature matches that of the lowest atmospheric temperature and surface emissivity=1
RJT flag
Output the Rayleigh-Jeans temperature spectrum (proportional to radiance, and commonly used in the microwave region)
GHZ flag
Specify spectral units are in GHz rather than cm-1. This applies to the numbers in the *SPC section as well as the output spectral file.
VVW flag
Apply the Van Vleck-Weisskopf correction to the Voigt lineshape, again commonly used in the microwave region.

In the *SPC section the resolution of 0.005 GHz corresponds to just under 6000 points per cm-1. If you run the standard RFM with this you'll probably get an error message saying that MAXFIN is too small. Increase the MAXFIN parameter in rfmsiz.inc to 6000 and recompile the RFM.

As a rule, it is usually necessary to use much higher spectral resolutions for microwave calculations than in the infrared in order to capture the Doppler width of lines (which scale as frequency or wavenumber, unlike the Lorentz width which remains constant). However, you can usually reduce the MAXWID parameter in rfmsiz.inc to c.10 in order to keep the memory requirements down (there are large arrays dimensioned as MAXFIN x MAXWID).

Driver Table

*HDR
04JUL17 RFM Example: nadir microwave
*FLG
   NAD SFC RJT GHZ VVW 
*SPC
   50 70 0.005
*GAS
  O2 H2O
*ATM
   ../atm/usa.atm
*SEC
  1.0
*HIT
  ../hit/hitran_2012.bin
*END

Output Files

Output Spectrum

[plot.pro]