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Orbital Dark Current Variation in 1991

Image name: Orbit_Dark_Variation_1991.png (click image to enlarge)
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Date submitted: 03-Jan-1994


     This figure compares the orbital dark current variation in 1991 with
the December 1994 results.  The 1991 data were collected in 7-8 November
with a DPE=28 exposure as part of a special experiment to look for hard
x-rays in the high corona (thanks, Hugh). 

     Although there is one "wild point" it appears from this comparison
that the response of the CCD dark current to UV flood is nearly the same
near mission beginning as at present.  The 1991 data have been shifted
vertically a factor of 3 to compensate for the overall increase in dark
current.  The points have also been shifted 128 sec to the right to
compensate for the fact that at this time we were using a 4 minute UV flood
-- the critical time is time after the end of the UV flood, not the
duration of the UV flood.  

     So, it seems that the UV flood through the aspect sensor optics was
sufficient to cause the effect and a single normalized correction will work
for the entire mission. 

					Loren Acton

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