Bad Pixel Update for Channel 3 as of 7/28/00
The fiber is gone!
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.
In July the infamous "fiber" was dislodged from the IRAC
Channel 3 flight array.
As before, to get this initial identification of the bad pixels, I have used
a technique similar to how observers pick out bad
pixels "by eye". Two sets of 5 images with the same exposure time from the 7/28/00 LFF were chosen.
The dead pixel identification was done using the transmission calibrator
test, and the hot pixels were identified using the zero point test. The 5 images
were median stacked in order to reject cosmic rays or other
transient glitches.
The bad pixels were identified on the basis of their being too high or low
relative to their immediate neighbors. The comparison must be done locally due
to the variable illumination from the calibrator. The median-stacked image was smoothed using a
running boxcar 5x5 median filter, and hence each pixel in the smoothed
image is an estimate of the local pixel value. The ratio of the median-stacked image
and the smoothed image was taken. Pixels with values less than half of
their immediate neighbors were tagged as "dead", and more than twice the
neighboring values as "hot". The identified pixels were checked by eye vs.
both the median-stacked image and the individual frames for aparrent
validity.
Previously, the major flaw in the Channel 3 array was the "fiber" which
resulted in the loss of about 100 pixels. The fiber is now gone. The array
has no dead pixels anywhere. It does seem to have two pixels with high dark
current within 2 rows/columns of the array edges.
By clicking on the image you can download a FITS format mask file. The
mask is an SSC pmask file.
