RFM File Formats

.fov File: Field-of-View

16SEP05
Type
Input, mandatory if FOV Flag enabled.

Description
Field of View response function

Filename
Specified in *FOV section of Driver Table

Structure
!CMNT [optional comment records]
NPT
ALT(1) ALT(2) ...
... ALT(NPT)
FOV(1) FOV(2) ...
... FOV(NPT)
[eof]

Fields
FieldTypeDescriptionRange
!CMNT C*80 Comment record(s) (optional) Record starts with '!'
NPT I Number of tabulated points |NPT| = 3:MAXFOV (in rfmsiz.inc)
Tabulated as Fn of altitude [km] OBS Flag disabled: NPT >0
Tabulated as Fn of elevation [deg] OBS Flag enabled: NPT <0:
ALT R*4 Altitude/Angle relative to nominal tan.pt. (no limits)
FOV R*4 FOV response at ALT FOV(1) & FOV(NPT) = 0

Notes
  1. A positive value of NPT indicates that the ALT values refer to altitudes relative to the nominal tangent point, while a negative value means elevation angles.
  2. Tabulation as a function of elevation angle is required if the observer altitude is specified (OBS Flag).
  3. There must be at least three tabulation points, of which the first and last values FOV(1), FOV(NPT) must be zero.
  4. The FOV function does not have to be normalised - this is performed within the code.
  5. The altitudes or elevation angles are normally interpreted as geometric altitudes, and the RFM allows for distortion by refraction during the ray-tracing. However, with the FVZ Flag these are treated as refracted values.

Examples 
! Trapezoidal FOV 2.8km / 4km @ 5 pt resolution
5  = No.tabulation points
    -2.0   -1.4   0.0   1.4   2.0
      0      1     1     1     0
[eof]

! Square(ish) FOV aperture of 2 deg full-width 
 -4  = No.tabulation points, negative implies angular separations in degrees
    -1.01 -1.0 1.0 1.01
      0     1   1   0
[eof]