.ils File

RFM File Formats: Instrument Line Shape

05MAY25
Type
Input(s), required with ILS Flag.

Description
(Apodised) instrument line shape function(s)

Filename(s)
Specified in *ILS section of Driver Table

Structure
All numerical data are read free-format
Files may concatenated
Header Section
!CMNT Comment record(s) (optional)
NPT   PT1   PTD   [WNOMIN   WNOMAX] Spectral axis [applicable spectral range]
Data Section
ILS(1) ILS(2) ... Tabulated ILS function, NPT values, multiple records
... ILS(NPT)
[eof]

Fields
Field Type Description Units Range
!CMNT C80 Comment record, starting with '!'
NPT I Number of tabulated points [2] |NPT| ≥ 2
PT1 D Relative Waveno/Freq of 1st Point cm-1 or GHz ≤ 0 (usually)
PTD D Spacing of Spectral axis [3] cm-1 or GHz > 0 (usually)
WNOMIN D (Optional) Lower Waveno/Freq for ILS use [4] cm-1 or GHz 0 < : < WNOMAX
WNOMAX D (Optional) Upper Waveno/Freq for ILS use [4] cm-1 or GHz > WNOMIN
ILS(NILS) D ILS Function [1]
Type: I=Integer; D=Double Precision; Cn=character string, length n.

Notes
  1. The ILS function does not have to be normalised or symmetric. After interpolation to the internal fine mesh grid it is renormalised. Zero values are assumed beyond the end-points.

  2. NPT: At least 2 points are required for interpolation. A positive value indicates a wavenumber axis, negative a GHz axis.

  3. PTD: The ILS function has to be tabulated on a regular Wavenumber/Frequency grid. It is best if this is also the internal RFM grid used for the finemesh calculation (usually 0.0005 cm-1). Functions specified on any other grid will be interpolated.

  4. WNOMIN, WNOMAX can be used to allocate ILS functions for specific spectral ranges, allowing multiple ILS functions to be applied in the same RFM run. If absent, it is assumed the associated ILS is the default function to be applied over any range not fully covered by one of the specific-range ILS functions. Consequently there should only be a maximum of one such ILS in the supplied .ils file(s). A fatal error message is generated if there is any ambiguity, or if there is no ILS function for one of the output spectral ranges.

Example
iasi.ils (IASI Gaussian-apodised ILS on 0.001 cm-1 grid)

Python Reader
read_ils.py