RFM Driver Table Sections

*OBS Section: Observer Location

28AUG17

Type
Secondary Section - depends on OBS Flag.

Description
Specify observer position in altitude [km] and, optionally, horizontal angle [deg].

Format
Single or (GRA Flag) two fields, identified by order.
FieldTypeDescription Range
1. ALTOBS R*4 Observer altitude [km] ≥ lowest point along ray path
2. PSIOBS R*4 Observer horizontal angle [deg] -90:90 (ignored unless GRA Flag enabled)

Notes
  1. Where the observer location is not specified (ie OBS Flag not enabled) it is assumed that the observer is somewhere between the top of the atmosphere and infinity - the precise altitude makes no difference if the path is specified by tangent height (either geometric or refracted) and the observer is somewhere outside the atmosphere. With the GRA Flag, all tangent points are then taken to lie at PSI=0.
  2. The actual range of allowed ALTOBS is determined by the viewing geometry specified in the *TAN section:
    • Limb-viewing paths specified by tangent point (*TAN or *GEO): ALTOBS ≥ highest tangent point
    • Limb-viewing paths specified by elevation angle (*ELE): ALTOBS within atmosphere for positive angles, low enough to interset atmosphere for negative angles
    • Zenith paths (ZEN Flag): within atmosphere
    • Nadir paths (NAD Flag): no restriction
  3. When the GRA Flag is specified (2D atmosphere), all viewing is assumed to be in the direction +ve to -ve horizontal angle, ie the observer location would normally be specified as a positive angle (subtended at the centre of the earth, so about 110km for 1 deg) relative to the atmospheric profile locations specified in the *ATM section.
  4. When used in conjunction with the GRA Flag, the observer location PSIOBS determines the horizontal angle of the tangent point(s) relative to the reference profile (PSI=0). This information is written to the .pth diagnostics file.
  5. See LEV Flag for method of generating outputs equivalent to multiple observer altitudes within a single run.

Examples
*OBS  
      25.0  ! Observer at 25 km. (1-D atmosphere)
*OBS
      25.0  4.0 ! @25 km. +4 deg from ref (2-D atmosphere).

Bugs
Bug#49 (Fixed v4.24)
Bug#48 (Fixed v4.24)
Bug#45 (Fixed v4.23)
Bug#68 (Fixed v4.28)