It is highly likely that when you reduce your Spitzer data, you will include the BMask files as input into SPICE. The pixels in the mask files all contain coded information, or "bit definitions", depending on the status of a particular pixel. For example, a pixel with bit 10 flagged in the BMask file indicates that that particular pixel in the data frame is saturated, while bit 14 indicates that the pixel was flagged as fatal in the PMask. For a full list of bit definitions, see the IRS Instrument Handbook or see Table 1.6.1 in this manual for a list of current BMask bit definitions. When running SPICE, you need to decide which of these codes you wish to set as "fatal", i.e. which of the flagged problems you consider so bad that the corresponding pixel in your data frame should be discarded. This is done by specifying a "Fatal Bit Pattern" as follows:

 

Fatal Bit Pattern = 2^{(value of 1st required fatal bit)} + 2^{(value of 2nd fatal bit)} + .... + 2^{(value of nth fatal bit)}

 

e.g. if you wished to set bits 7, 8, 9, 10 and 14 as fatal for your IRS BMask file then your BMask Fatal Bit Pattern would be: (2⁷ + 2⁸ + 2⁹ + 2¹⁰ + 2¹⁴) = 18304.

 

The most up-to-date recommended Fatal Bit Patterns can be found in the IRS Instrument Handbook.