subject:  flatfield of 2005 for Detector-A


The deterioration of the ADC of Detector-A has been progressing during 2004 and 2005. 
For most of the time the short slits at the bottom of the detector (Slit 5, Slit 8) could be 
used only. Even some parts of this field-of-view are not usable anymore. 
However the part between pixel rows 10 and 59 was and still is usable for many types 
of observations on the solar disk.
The data have to be treated with caution however: the standard flatfield and distortion 
matrices are for most cases not accurate enough, because their pattern has changed 
due to several reasons. 
- The odd-even pattern, which is normally contained in the flatfield image, has increased 
due to the ADC failure. 
- The geometric distortion data have not been accurate at the lower part of the detector 
from the beginning, and there is some evidence that it has changed with time, because 
it may be dependent on the temperature of the delay-line anode which has changed 
during the mission.
 
For the new data of 2004 and 2005 (and hopefully 2006) with Detector-A new flatfield 
and distortion data will be needed. We have therefore produced a flatfield image from 
recent data that can be used for this lower part of Detector-A. 
The array ff_a_20051011_d_r.rst can be found at the usual place in the data base, 
e. g., in IDL format in the "ff" subdirectory
http://sohowww.nascom.nasa.gov/sdb/soho/sumer/calibration/flight/ff/ 
or in FITS format in the "flatfield" subdirectory.
(Note, only the part of the data is useful where values are larger than 0.5!)
 
 
The calculation of a new distortion matrix is more difficult and will take some time. 
Until a new distortion matrix is ready the old one can still be used.
 
 
Udo Schühle
Katlenburg-Lindau, 4. November 2005