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I have now spent some time looking at the spreadsheet, and I've tried a number of different systems. The all-important knee of the S/N vs sub time curve is consistently close to my calcs.
There is one issue:
The S/N results for stacked performance may be optimistic unless dithering is assumed. This is because with undithered subs, stacks are not re-sampled for registration. My understanding is that under these conditions calibration frame noise builds up with the number of subs, which may result in additional noise. If the number of subs is vastly lower than the number of subframes in the calibration frames, the noise increase is negligible. And of course if there is a large number of calibration subs, the noise from that source is low anyway.
I have not checked the maths myself, so I can't be definitive about it, but perhaps it is worth adding a note to the spreadsheet recommending dithering (and lots of calibration subs)?
Mark
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