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Stochastic factors are
- seeing
- cloud cover
This suggests that we define a quantity point source photometric merit factor (PSPMF) that tracks how a given image contributes to SNR per band, where
PSPMF=sqrt(t/15)*(T/1)*(1/FWHM)*(sqrt(1/sky)).
with T=atmospheric transmission, which depends on both cloud coverage and airmass and t=exposure time. Summing this quantity over all visits to a given location would provide a cumulative photometric merit factor.
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Oct 18 2013, C. Stubbs
Observations obtained at angles z from zenith suffer from two effects:
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Operating on the meridian in this mode, with 15 second exposures we'll assume it would take 20 seconds total on average, per exposure. It would take 24*(3.1/360)~12 minutes for the sky to move by one field width, on the equator. In the course of 12 minutes we can acquire 12minutes*3images/min=36 images on the meridian. At this half-overlap rate we could cover 36*3.1/2~56 degrees.
Coverage Rate
At 35 seconds per visit and 9.6 square degrees per field, we cover the sky at a rate of 7900 square degrees in an 8 hour night. That means that on average we revisit interval (no weather) is 3 days for 18,000 square degrees.
Sky rotation.
The position of objects on the sky changes in right ascension direction at an angular rate of 15 degrees per hour times cos(declination).
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