Overview
The Instrument Line Shape (ILS) file
represents the spectral convolution function Ψ
applied to the monochromatic input spectra τ(ν)
by the HIROS instrument, so that
the convolved transmittance τ0
reported at nominal spectral point ν0 actually represents
τ0 = ∫ τ(ν) Ψ(ν-ν0) dν
The ILS is tabulated as Ψ(νi-ν0)
on a regular spectral grid defined by
(νmin, Δν), so that
νi-ν0 = νmin + (i-1) Δν
Normally, νmin < 0 and
Δν > 0 is expected,
although signs could be reversed, or even the same (implying no overlap
between the ILS and the nominal spectral point ν0).
The ILS file used within the Cubemap E2E Simulator is the
RFM .ils file format.
Example: hiros.ils,
which can be read with the IDL function
read_ils.pro
File Structure
The file contains a header section consisting of a single non-comment record
containing the spectral axis parameters.
This is followed by a data section consisting of the tabulated ILS function
spread over as many records as required.
All numerical data are read "free-format".