[Laser] Astronomy frame stacking software

[James Whitfield]

If the intent is to communicate with weak optical signals, perhaps we should
consider the tools used by astronomers, such as CCD imaging devices and
image stacking software.  It requires some re-thinking and throwing out the
idea of using a sound card or frequency spectrum software.  These are used
to detect and integrate photons from weak sources.

The image stacking software sifts through hundreds of frames to improve the
end result image.  The communication task would be to separate the frames
into a time sequence of bright and dark.  The sequence might represent the
transmitted tone of a modulated signal, but the time scale would be many
times slower than can be processed by a sound card.

Suppose that you have a message that lasts about three minutes if sent as a
1 baud BPSK signal with a carrier tone of 1 Hz.  If the CCD is sampling 10
frames per second, you get about 1800 frames.  With the modified image
stacking software, you look for clusters of pixels that fit the pattern of 5
or 10 frames of increased brightness followed by 5 or 10 frames without.
Then you rescan the images to find the synchronization, which is basicly
choosing the grouping that minimizes the sets of 10 frames that show more
than 6 bright.  Then group the images ten at a time, if the first 5 are
brighter than the rest, it is a one, if the last five are brighter it is a
zero.


James
N5GUI