## .fov File | ||

## RFM File Formats: Field-of-View Data | ## 23FEB24 |

**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(:) R (NVal) Altitude/Angle ^{[2]}relative to nominal tangent pointkm or deg ± values expected FOV(:) R (NVal) FOV relative response at Alt ^{[1]}^{[4]}≥ 0 expected **Type**: I=Integer; R=Real; Cn=character string, max length n. **Notes**-
- At least three points must be specified with FOV(1) = FOV(NVal) = 0 to define vertical extent of the finite FOV response.
- 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*. - Tabulation as a function of elevation angle is
*required*if the observer altitude is specified (OBS Flag). - The FOV function does not have to be normalised; this is performed within the code.
- 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