*GEO Section

RFM Driver Table Sections: Ray Path
06AUG24
Type
Primary Section#6
Variation of *TAN section.

Description
Geometric tangent height(s) of ray-path
(i.e. projected tangent height in the absence of any refraction)

Format
Multiple fields[1], any order
Field Type Description Units Range
GEO R Geometric tangent height km −RadCrv[3] : TOA[4]
GEOFIL C200 Name of a Data File [1]
Type: R=Real; Cn=character string, length n.
RadCrv = Radius of Curvature; TOA = Top of the Atmosphere

Notes
  1. GEOFIL: The type of field is identified by first using the Fortran INQUIRE statement to see if it is a file (assumed to be a .dat file), in which case the file is opened and the numbers read from the file as if they were directly inserted within the section at that point. This can be used in combination with actual numerical fields.

  2. GEO: The tangent height is relative to 0 km in the *HGT profile (which is not necessarily the surface), supplied in the *ATM section. Tangent heights must generally be distinct to 5 significant figures (1m below 100km, 1 km above 100km) so that they give distinct output filenames otherwise a 'Repeated Tan.Hgt' fatal error message results.

  3. Unlike with refracted tangent heights (*TAN section), using geometric tangent heights allows ray paths to be specified which intersect the surface. The minimum value, −(RADCRV), corresponds to nadir-viewing.

  4. For an observer within the atmosphere (OBS Flag) the maximum tangent height is the observer altitude (HGTOBS), corresponding to a horizonal view, otherwise it is the top of the atmosphere.

Example
*GEO -10 0 10 ! list of geometric tangent heights (in km)

Bugs
Bug#10 (Fixed v5.02)