.fov File

RFM File Formats: Field-of-View Data

11JAN25
Type
Input, mandatory if FOV Flag enabled.

Description
Field of View response function

Filename
Specified in *FOV section of Driver Table

Structure
The file contains a header section consisting of an arbitrary number of initial comment records followed by a single record containing a single number: the number of tabulated points.

If the number of points is positive, this indicates that the vertical coordinate is altitude; if negative, then angle.

This is followed by the list of altitudes/angles, spread over as many records as required, then, starting with a new record, the tabulated FOV function, also extending over as many records as required.

All numerical data are read 'free-format'.

File Structure
!CMNT Comment record(s) (optional)
NVAL No. of tabulated values
ALT(1) ALT(2) ... Altitude/Angle coordinates as block of NVAL numbers
... ALT(NVAL)
FOV(1) FOV(2) ... FOV function as block of NVAL numbers
... FOV(NVAL)

Fields

Field Type Description Units Range
!CMNT C80 Comment record first character is '!'
NVAL I No. tabulated data points |NVAL| ≥ 3 [1] [2]
ALT(NVAL) R Altitude/Angle[2] relative to nominal tangent point km or deg ± values expected
FOV(NVAL) R FOV relative response at Alt [1] [4] ≥ 0 expected
Type: I=Integer; R=Real; Cn=character string, max length n.

Notes
  1. At least three points must be specified with FOV(1) = FOV(NVAL) = 0 to define vertical extent of the finite FOV response.

  2. A positive value of NVAL indicates that the ALT values refer to altitudes relative to the nominal tangent point, while a negative value means elevation angles.

  3. Tabulation as a function of elevation angle is required if the observer altitude is specified (OBS Flag).

  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.

Example
mipas.fov (MIPAS trapezoidal FOV)

Note the use of a central point (at 0km) which doesn't change the shape of the FOV but does force the RFM to calculate an extra ray-path at the nominal tangent height rather than interpolating between ±1.4 km.

Python Reader
read_fov.py