WHIRC Reports


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WHIRC Reports

Several in-house reports were written during the commissioning process. These cover aspects of the instrument performance in more detail than presented on this webpage.



Mean-variance Plot

The mean-variance (photon transfer) measurement is used to determine both the read noise and gain (e/ADU) of the detector. This analysis assumes the only sources of noise to be the signal-independent read noise and the shot noise from the signal itself. When the variance of the signal is plotted against the mean value on a log-log plot, the result is a line of unity slope in the photon-noise-limited regime which intercepts the X-axis at a value equal to the gain. The Y-intercept of the actual data is the variance of the read noise. The data from September 2008 and more recent data from November 2009 were analyzed using the sum/difference technique described in Schubnell et al. (2006, SPIE, 6276), in which the variance of the difference of two images is plotted against mean of the sum. For both of the data sets, this yielded a conversion gain significantly smaller than that determined using a temporal variance on a pixel-by-pixel basis. Analysis of model data with known read noise and gain using the sum/difference technique returned the correct values, whereas the temporal analysis returned gain values about 10% larger, so we have accepted the 3.3 e/ADU gain obtained by the sum/difference analysis. The complete report (WHIRC Report VI) may be downloaded from the preceding list.

rjoyce@noao.edu
29 October 2010