Bandwidth Correction Verification (5/2/01)



Note: the following information is intended for the IRAC instrument team only. If you are not such a person, you should not be reading this. No guarantees are made as to the applicability of this information to the real IRAC.



The bandwidth correction coefficients have been previously derived for the flight system from cosmic ray data. Unfortunately, this points a critical verification problem - lack of suitable test data to evaluate the efficacy of the bandwidth correction module. The ideal test data would be images with a single illuminated pixel. The best IRAC can do is a point source which covers a few. Moreover, the GSE since integration of IRAC with the flight cables (at BATC) has not had this capability. We will get something vaguely point-like during the Brutus test (in dec-jan), although it will be somewhat extended, and that is all there will be until flight.

As a quick check, we have run the EBWC module on an image with noticeable cosmic rays. This data is stored in 

/ssc/testdata/irac/preflight/ebwc/array1
/ssc/testdata/irac/preflight/ebwc/array4


Ch.1 Radhit (before EBWC)After EBWC

Ch.4 Radhit (before EBWC)After EBWC


The top images show a radiation hit of intensity roughly 15,750 DN in channel 1. The "echo" that follows it (in the left-hand image) is roughly 19 DN, which is 6 sigma above the local mean. On the right is the result of applying the bandwidth correction module with the as-measured coefficients. After correction the pixel in question is 1.9 sigma below the local mean. The ch.4 data is 2 sigma high and 1 sigma low. Given the small number of measurements used to derive the coefficients (typically less than 5) this is acceptable in terms of our pre-flight knowledge. The coefficients will have to be further refined in-flight.

Jason Surace (5/02/01)