RFM Examples

Nadir Brightness Temperature, Curved Atmosphere

23FEB21


Description

Off-Nadir viewing Brightness Temperature through the US Std Atmosphere allowing for Earth Curvature and refraction (this is the more accurate version of the example using the Plane Parallel approximation).

*FLG section
OBS flag: to specify observer location within atmosphere
BBT flag: to generate brightness temperature spectra
SFC: to specify surface characteristics
*ELE section
Use of *ELE as a section marker (instead of *TAN) indicates that path will be specified as an elevation angle relative to horizontal (-80 degrees being 10 deg off-nadir). Although this runs the RFM in its default 'limb-viewing' mode, the path intersects the surface so that the usual specification of a limb path by (refracted) tangent height cannot be used, hence the need to specify ray path by observer altitude and elevation angle instead.
Actually path specification by geometric tangent height (*GEO) could still be used, but that would probably require the user calculating this distance using the information they would supply anyway for the *OBS and *ELE sections here).
*SFC section
Specify surface temperature and emissivity. Since the temperature in the US Std Atmosphere is 288.2 K at the base of the atmospheric profile, these would have been the RFM default values anyway, so the *SFC section isn't actually required in this case (although the SFC flag in the *FLG section is still necessary to acknowledge that the surface is being viewed).
*OBS section
Specify the observer altitude at 800 km above the surface.
*PHY section
Specify the Earth local radius of curvature. In the absence of this section the default value of 6367.421 km (in phyadj_dat.inc) would have been used instead.

Driver Table

*HDR
23FEB21 RFM Example: nadir bbt, curved atm.
*FLG
   OBS BBT SFC
*SPC
   1220 1230 0.1
*GAS
  CH4 H2O N2O
*ATM
   ../atm/usa.atm
*ELE
  -80.0
*HIT
  ../hit/hitran_2012.bin
*SFC
  TEMSFC=288.20 
  EMSSFC=1.0
*OBS
  HGTOBS=800.0
*PHY
  RADCRV=6400.0
*END

Output Files

Output Spectrum

[plot.py]