Documentation > SXT Observation Notes > this page

Variation of SXT Straylight

Image name: Orbit_and_Pntg_Straylight.png (click image to enlarge)
Image size: 19.9340 KB (800x980)
Date submitted: 19-Feb-1995


These plots display the results of an experiment ran 16-Feb-95 to study
the orbital and pointing variation of straylight with and without the ND
filter.  One 64x64 HR pfi was located on the Al.1 big pinhole in the SE. 
A second was put on the strong straylight lobe in Be/ND near the LH side
of the CCD.  The experiment was run at QT/H for two visible orbits. 

While the dark-corrected Be/ND signal was pure straylight the Al.1
signal was somewhat contaminated with x-rays.  This is evident from the
time plots at the top which show the Al.1 signal beginning to decrease
about 100 seconds before sunset -- the Be/ND signal (as expected) shows
no such effect.  

The Be/ND plot reveals a linear decrease of straylight signal through
the orbit of about 2.7%.  This is larger than the orbital decrease of
roughly 1% that I derived from NB aspect images for the period before
filter failure (after I had removed the long term decrease).  I am
guessing that this variation in sensitivity to visible light is an after
effect of the UV flood.  The flood now is much more intense than before
the filter failure. 

The Al.1 plot combines this orbital variation with a stronger variation
that is dependent upon pointing -- as expected.  In this case the limb
of the poorly focussed optical solar image falls directly on the pinhole
so is very sensitive to pointing.  The lower left plot shows no pointing
correlation with straylight, all variation here is from the correlation
of pointing and time after FMS.  This is expected as the ND filter
should totally smear out any small effects due to pointing changes.  It
may be possible to improve straylight correction with a time-since-fms
factor but this will require additional calibration.  It may not be
worth the effort as the effect is minor.

						L. Acton 2/19/95

To the YLA Guide front page with side-frame
To contact us: