The weighting scheme of
CLASS was slightly inconsistent when summing
or averaging spectra observed in different observing modes (frequency
switching, wobbler switching, and position switching). A first attempt at
solving this problem that was implemented on Sep. 17th, 2019, led to
incorrect system temperatures in the output spectrum when averaging or
summing folded frequency switched spectra. This in turn brake the
associativity of the average or sum commands: When averaging three folded
frequency switched spectra S1, S2, and S3, the noise level of (S1+S2+S3)
was slightly different from the noise level of ((S1+S2)+S3)).
In this memo, we describe the problem and propose a solution that was
implemented in the mar21 release of GILDAS. We ask all our users that
currently use a version of GILDAS between oct19 and feb21 to update
their version to the newest one.
Keywords: CLASS Data Format
Related documents: Averaging spectra with CLASS (memo 2009-4),
MRTCAL user manual.