FAQ: wavelength to frequency

Frank Valdes wrote on Feb 20, 1998

Q:  Is there anyway or package available to convert a wavelength
spectra to a frequency spectra (in iraf).


A:  There are two possibly answers to your question.  The first is that if
you want to display spectra in frequency then you can change the
display units.  For example with SPLOT you can set the units as a
task parameter or type ":units ..." interactively.

If you want to change the dispersion relation in the image or resample
the image to uniform (linear) increments in wavelength then you
would use the task DISPTRANS in the ONEDSPEC package.  Here you specify
the desired units in the same way as for display.  If you don't linearize
you end up with a complex dispersion function in the header and if you
do linearize you get the usual CRVAL/CDELT type of dispersion but
in the desired units.

Help on the units syntax may be found by typing "phelp onedspec.package".

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Last post on Feb 20, 1998