Nadir Brightness Temperature, Curved Atmosphere
RFM Examples		20SEP23

Description

*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 20SEP23 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

• bbt_-80000.asc
• rfm.log

Output Spectrum

• RFM Examples