RFM Flags

NAD Flag: Nadir-Viewing

15SEP05
Enabled
Calculate spectra viewing downwards into a plane parallel atmosphere
*TAN (or *SEC) section of Driver Table specifies airmass factor for calculation (eg, 1.0=vertical, 2.0= 60 deg to vertical)

Disabled
Assume limb view (or other geometry)

Restrictions
SFC Flag must also be enabled.
Incompatible with CRV, FOV, GEO, GRA, HOM, LOS, TAB, and ZEN Flags.

Notes
  1. The plane parallel atmosphere allows several simplifications: no refraction, no field-of-view effects, analytical Curtis-Godson path parameters, which are valid for direct nadir viewing but approximations for slant paths. For exact downward views in a spherical atmosphere it is still possible to use the normal limb-viewing calculation (eg with negative geometric tangent heights, replacing *TAN section label with *GEO).
  2. Use of FLX Flag redefines NAD flag.

Bugs
Bug#77 (Fixed v4.29)
Bug#23 (Fixed v4.12)