IRAS Explanatory Supplement
XI. Known Processing Anomalies
D. Errors in Cross-Scan Uncertainties Related to Failed Detectors
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Several changes were made in the course of the processing
to ameliorate the effects of failed detectors. While all of the
changes Resulted in overall improvements, the last change introduced
an error as well. The last change handled the situation when an
edge detection occurred opposite a failed detector and when the
fluxes of the detections differed by more than a factor of two,
so that the detections failed to seconds-confirmed. Since only
one detection could band-merge with the rest of the source, an
improvement was made to select always the brighter detection and
to delete the fainter one. An error in the software assigned
a wildly incorrect cross-scan uniform uncertainty to the remaining
detection one-third of the time.
This change still resulted in a net improvement in the quality
of the sources. The erroneous cross-scan uncertainties were immediately
eliminated if band-merging was successful. A problem was created
when the faulty detection was merged with another real source
that had transited the focal plane at precisely the same time.
No restriction on cross-scan position existed because of the impossibly
large cross-scan uniform uncertainty associated with the detection.
The resulting incorrectly band-merged source failed to have upper
limits from being assigned to unobserved (or unmerged) bands.
Thus, the Working Survey Data Base (WSDB) contains some hours-confirmation
with some bands with FSTAT = 0, and detectors all 0 (see
Section
V.D.8). A detailed comparison of the processing of the data with
and without this error showed that no sources with signal-to-noise
ratio greater than 9 were lost due to this error.
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