UVCS/SOHO Post-Sept.'97 LYA Flat Field

UVCS/SOHO post-Sept.'97 LYA flat field

Peter L. Smith, Nigel Atkins & Raid Suleiman

with help from L. Gardner, J. Kohl, R. Frazin, and others

The flat field data for the LYA detector "today" (i.e., after the voltage reduction in Sept.97) that were displayed and discussed at the UVCS Science meeting in Maine (September 1998) are available:

To download the file hold the shift key and click here

Let rsuleiman@cfa.harvard.edu know if you have any trouble retrieving them.

The image below shows the whole detector.

The figures below show the relative response of columns 350:950.

Note that the dark current is not uniform, but is lower where the detector efficiency is lower.

Some caveats:

  1. The "flat-fielding" in the spatial direction is based: This process could lead to small (5% perhaps) systematic errors in the macroscale (i.e., over large areas) flat field in the spatial direction.

  2. The flat-fielding in the spectral direction was done by observing scattered disk light on three occasions:

    binningsource function
    760:870 3 x 1 measured by the method discussed in (1) above
    610:780 3 x 1 measured, but the portion of the OVI detector that was used seems to have deteriorated by 8% between the two sets of measurements. Therefore, this region was flat-fielded by comparison to 760:870 in the region of overlap.
    415:640 6 x 1 not measured; flat-fielded by comparison to 610:780 in the region of overlap.

    Again, there is a possibility of small (5% perhaps) systematic errors in the macroscale flat field. Estimation of these is problematic.

  3. The edge effects (columns ~420 and 875; row ~35) are actifacts. They do not indicate actual performance of the detector at these locations.

statistical thoughts

We sampled two "undamaged" portions of the detector.

rowscolumnsbin size
(rows x columns)
standard deviation
100:270459:5106 x 111%
100:270798:8543 x 18%

The statistical uncertainty of the data is estimated to be +/-3%.

last update 3 February, 1999, by R. M. Suleiman