[Laser] Astronomy frame stacking software

[James Whitfield]

From: "Art" <KY1K at verizon.net>

> I'm not sure most of us can use the benefit of an expended field of
> view on receive, but it would certainly be useful in some cases.
>
> I'd love to be able to go to a hilltop, aim my receiver in the
> general direction of my qso partner and be assured that I didn't have
> to worry about aiming the receiver! But, these ccd's need serious
> cooling to make them work with long term averaging. The good ones aren't
cheap.
>
> I'd rather cool my photodiode than to attempt to cool a CCD unit. I'm
> just not sure most amateurs would find them useful.
>
> Art
>
First I want to state that I am only thinking here in terms of very weak
signals, and only if the signals can be collected by the astronomy devices
and software, or derivative therefrom.

Also I should correct a fundamental oversight:  The term CCD refers to the
charge coupled device technology to store and transfer charge in shift
registers which then drive serial outputs.  The charge for each pixel is
generated by ( and someone correct me if I get this wrong ) rows or arrays
of photodiodes.  In any case the idea here is that photon are converted to
electrons, stored as charges which can then be read by computer devices
which can then be processed into images for astronomers, or as I suggest
communication.  In that respect I submit that the reason that the "good
ones" are cooled for the same reason that it has been suggested that cooling
photodiodes is good for communication experiments.

I have posted ideas on field of view issues before, but I fear that they
were not communicated well.  I often have trouble trying to figure out what
it was that I was trying to say.

The pixel size of a typical image device ( and the other competitive device
to CCD is CMOS, lower cost, higher noise, smaller fraction of chip surface
active ) is 10 to 20 micrometer.  In a 128 X 128 array that means the active
area is 1 - 2 mm.  Assuming that you have an optical tube that is 900 mm
focal length, each pixel is going to "cover" 11.1 micro-Radians, or less
than 3/4 inch at one mile.  The entire array covers over seven feet.  Now if
the signal you are trying to process is near the noise level, I think that
being able to isolate one pixel of signal plus noise from 16,383 pixels of
just noise is a benefit worth pursuing.  Even if that one pixel changes its
position on each frame.  Maybe the source bleeds over a few dozen pixel.  I
still think it is worth considering.

I am not trying to put down anybody's approach, or equipment.  Astronomers
have been at this a lot longer than we communication experimenters.  They
might be able to show us how to build a wheel instead of us having to invent
a new one.  They are not always trying to look at tiny stars.  But when they
do, they use bigger and more precise light buckets, and try to find darker
skys.  Well, most of the time that is what they do, sometimes they try
something different.

James
N5GUI