IRAC Instrument Handbook - IRSA - California Institute of Technology

IRAC Instrument Handbook
Figure 5.2: INSBPOSDOM works only on the two InS b arrays (Channels 1 & 2) and reverses the sense of
intensities.
5.1.5 CVTI2R4 (byte type changing)
Data are converted from the native unsigned 16-bit format used by IRAC to the 32-bit floating point
format used in astronomical calculations. At this point, the following DN is added to all pixels in order to
account for the bias introduced by the spacecraft on-board bit truncation.
−0.5 x (1 − 2 −ABARREL ) for channels 1 and 2
+0.5 x (1 − 2 −ABARREL ) for channels 3 and 4
Here, “ABARREL" is the barrel-shift number keyword where the bit truncation occurs (see Section
5.1.7). Also, if the header indicates that any rows or columns are blank (usually due to data loss during
transmission from Spitzer to the ground), then those pixels are set equal to NaN’s.
Pipeline Processing 72 Level 1 (BCD) Pipeline