Nadir Brightness Temperature, Curved Atmosphere

RFM Examples

22NOV25

Description

Brightness temperature spectrum viewing off-nadir 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 22NOV25 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_2016.bin *SFC TEMSFC=288.20 EMSSFC=1.0 *OBS HGTOBS=800.0 *PHY RADCRV=6400.0 *END

Output Files

Output Spectrum

[plot.py]