Without any spectral convolutions
(no ILS or
AVG Flags) the RFM generates spectrally sampled
output at the resolution RESSPC
specified in the *SPC
section of the driver table, so this is
also fine mesh resolution for calculations.
However, if any spectral averaging
is required, either by an explicit instrument line shape convolution
(ILS Flag) or using the
AVG Flag,
the fine mesh resolution for the calculations defaults to 0.0005
cm-1 (set by 1/DEFFIN in rfmcon_dat.f90),
irrespective of the output resolution, unless modified by the value
supplied here.
The RFM default value of 0.0005 cm-1 is appropriate
for mid-infrared limb-viewing calculations, and is set by the requirement
to capture the area of Doppler-broadened lines (typical half-width
0.001 cm-1). For nadir-viewing infrared, 0.001 cm-1
is considered adequate. The Doppler width
narrows in proportion to wavenumber, so microwave limb-viewing is the
most extreme case where a value
of 30 000 is required to fully capture the Doppler core of a line.
If grid spacings larger than 1 GHz are required, these have to be expressed
in points per wavenumber (1 GHz being approximately 30 pts/cm-1).
[this seems unnecessarily obtuse - I should probably fix this!]
Example
*FIN
1000 ! Set internal grid to 1000pts/cm-1 (0.001 cm-1 spacing)
