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Date submitted: 06-Jun-1996
On Orbit Measurement of SXT CCD Electronic gain Special observations of the Al.1 pinhole image were made on 19-Apr-96 to check the SXT CCD gain (electrons/DN). The panels show: Upper left, top: Average of the 30-sec exposures of the pinhole, 128 x 64 Full-res PFI. Upper left, bottom: Variance image from the same exposures. The south coronal hole is at the upper right. The weak X-ray flux (about 1 % of the optical) produces high variance because of pointing drift, solar evolution, and the large number of photoelectrons per x-ray photon. Only the bottom 11 rows are used for the gain measurement to avoid the X-ray flux. Upper right: Distributions of the intensity residuals after subtracting the average image for 3.7 sec (+) and 30 sec (x) exposures. The distributions are Gaussian and the fits, plotted as lines, were used to measure the variance. A low order polynomial surface is used to account for the slow variation in the pinhole image shape/brightness when each image is matched to the average. Lower left: The raw variance is corrected for systematic effects, including the bias in the A/D converter: twice as many pixels have even data numbers than have odd. Lower right: A linear fit of variance against intensity has a slope whose inverse is the gain. Values for camera parameters are: Canonical Measured Bias 13 14.9 +/- 0.1 DN Gain 100 87.9 +/- 1.4 e-/DN Read noise 20 46 +/- 19 e- Submitted by Barry LaBonte June 6, 1996
