IRAS Explanatory Supplement
V. Data Reduction
D. Point Source Confirmation
D.2 Overview of Seconds-Confirmation
D.2.c Optical Crosstalk Removal
Table of Contents | Index | Previous Section | Next Section
Each detection was checked to see whether it was bright enough to cause spurious sources due to optical crosstalk on adjacent detectors (see Section VII.E.5). This decision was made on the basis of the bright source's signal-to-noise ratio, since the detection process triggered on that parameter, not flux level. For example, a source which might elicit optical crosstalk detections in quiet sky might not do so in the Galactic plane, where the higher noise level could mask the crosstalk.
A lookup table for each band was used to determine the cross-scan distance over which a source might cause optical crosstalk detections. This was a function of the signal-to-noise ratio of the source, and was based on the prelaunch evaluation of the optical point-spread function. The signal-to-noise ratio thresholds for closer examination were 5000, 1200, 300, and 200 in the 12, 25, 60, and 100 µm bands, respectively. When a detection was above this threshold the cross-scan distance to search for other detections caused by crosstalk was obtained from the lookup table. The in-scan search distance was constant, with values of 14", 14", 29", and 58" in the 12, 25, 60, and 100 µm bands, respectively. Any detections in the window which were fainter than the one being processed were deleted from further consideration. The deletions were performed only for the module containing the detector which yielded the bright source, in order not to eliminate its confirmation partner.
No attempt was made to identify crosstalk caused by the secondary mirror support spider. The characteristics of the bright source and those deleted were subsequently used in the small extended source processing. An analysis of the effects of bright sources is given in Section VII.E.5.
Table of Contents | Index | Previous Section | Next Section