This paper summarizes the error propagation of the SWS pipeline. It is
not possible to list all cases. Only the standard pipeline data processing
will be discussed. Also it is not intended to discuss error handling in
associated CAP procedures, although they influence how the pipeline is
treating errors. This might be subject of further versions.
This study is based on pipeline version 6.0. During this study it turned out that it is possible to improve the error handling of this pipeline version. Thus a few modifications were done within the IA3 environment (SPR_S0166). Especially the DERIVE AAR s/w changed drastically in some cases of the error computation. This paper will note the differences between the current pipeline version 6.0 s/w and the current IA3 implementation.
A list which pipeline modules were affected is appended to this paper.
The computed errors in the Auto Analysis product do not reflect all
known uncertainties to the 'flux' value in the AAR. An attempt has been
made to correctly propagate the detector noise through all steps of flux
calibration, and to include other effects like the statistical error of
dark current measurements. There are, however, effects like slow detector
drifts which may significantly affect the measured flux but cannot be
precisely quantified. The 'stdev' is hence more a number which might be
suitable for comparison purposes, e.g. assessing which part of the
spectrum are 'more noisy', than for quantifying the absolute uncertainty
in (continuum) flux.
Due to technical reasons it is not meaningful to compare errors of different
detectors. It is more intended to give an impression about the relative
errors for one detector.
Although the current error propagation is on a 'best knowledge base' this paper should be the base for further discussions. It should be updated with every pipeline update in IA3 which affects error computation