IRAC Instrument Handbook - IRSA - California Institute of Technology

where
IRAC Instrument Handbook
x = log10(pixel number +1) (5.10)
Pixel numbers are counted along the detector readout direction, starting from the muxbleed causing pixel
(pixel number zero).The muxbleed pattern appears to be independent of readout channel, Fowler
sampling, etc. Furthermore, the pattern seems to be applicable to both the channel 1 and channel 2
muxbleed, with a slightly different scaling factor.The severity of muxbleed depends on the brightness of
the bleeding pixel. Muxbleed scaling laws as a function of the bleeding pixel were obtained for channels 1
and 2. They are
where
2
⎛
⎞
⎜
1 ⎛ x − B ⎞
ScalingFac tor = A⋅
exp − ⎟
⎜
⎜ ⎟
(5.11)
⎟
⎝
2 ⎝ C ⎠ ⎠
x = log10(bleeding pixel intensity in DN). (5.12)
For channel 1, A = 0.6342, B = 5.1440 and C = 0.5164. For channel 2, A = 0.3070, B = 4.9320 and C =
0.4621. Both the scale factors and the muxbleed pattern are fixed for all pixels in a given array. Muxbleed
from triggering pixels with brightnesses below 10,000 DN is not corrected, because the corrections in
these cases would be just a few times the read noise. Muxbleed is also not corrected in the subarray
observations.
Observers should note that calibration darks are not muxbleed corrected. Muxbleed occurs in these
images due to the presence of hot pixels. However, this occurs equally both in the darks and in the science
frames and has been found to subtract noiselessly from the science data. Thus, any dark frame muxbleed
is simply considered a feature of the darks.
Note that the muxbleed correction decribed here does not correct 100% of the muxbleed effect.
5.1.12 DARKDRIFT (``readout channel’’ bias offset correction)
Each IRAC array is read out through four separate channels. The pixels read out by these channels are
arranged vertically, and repeat every four columns. Small drifts in the bias levels of these readouts,
particularly relative to the calibration dark data, can produce a vertical striping called the “jailbar" effect.
Pipeline Processing 81 Level 1 (BCD) Pipeline