## Nadir Brightness Temperature, Curved Atmosphere |

`*FLG` section
includes the `OBS` flag to show
that observer altitude is specified, and the
`CRV` flag to show
that the earth's curvature is supplied
(default is to assume RFM default
curvature of 6367.421km).

`*ELE` section specifies the
path 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, so the
alternative definition of path by observer altitude and elevation angle is
used 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`,
`*ELE` and
`*CRV` sections here).

`*OBS` section specifies that
the observer altitude is 800km.

`*CRV` section specifies that
the local radius of curvature is 6400km.

*HDR 20AUG13 RFM Example: : nadir bbt, curved atm. *FLG OBS CRV BBT SFC *SPC 1220 1230 0.1 *GAS CH4 H2O N2O *ATM ../atm/usa.atm *ELE -80.0 *HIT ../hit/hitran_2012.bin *SFC 288.20 1.0 *OBS 800.0 *CRV 6400.0 *END