# WHIRC Reports

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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