adk: Averaged Scaled Dark Frame Image

adk is the averaged, scaled dark frame image which is used by VMBICAL to dark-correct the raw solar intensity measurements. At each site, several calibration images are acquired by the instrument each day. One of these is a raw dark image which is taken with no light incident on the CCD. The dark image format is identical to the solar image format - the image is measured with an array of 1024×1024 pixels and consists of three interleaved intensity measurements. However, a dark observation is taken for 56 sec.; whereas a solar observation lasts 60 sec. This means that the dark image must be scaled by 60/56 before being applied to solar images. adk is calculated from the dark image by averaging the three interleaved intensity measurements and then multiplying by 60/56.

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