[Laser] Big adaptive optics

Fri Sep 21 23:58:37 EDT 2007

Seems like an awful lot of hoopla from the California Institiute of
Technology if all they have done is to mount amateur equipment and software
on their big light bucket.  Even presuming they would have used an imaging
device that is higher resolution and better quality than a "standard video
camera", I would have expected a different processing technique than the
software you describe.

However, I certainly would not have the expertise to know what they are
doing from the description that I read.  Oh, I think I understand the
mathematics of averaging, or noise subtraction, or contrast exageration.
There is a lot more out there that I don't understand.

The software you have described certainly would seem to to have some
potential for adaptation for slow transmission rate signals.  That is a case
where On-Off Keying of slow versions of Morse, ASCII, or Varicode could be
sent, then received by some optics that are image quality, captured by video
equipment affordable by amateur astronomers, then processed into images.

This might make the NLOS systems more viable.  Cloud bounce.  Beam scatter
over an obsticle, like a ridgeline.

Whatever the method, I would think that you would need to be able to define
an envelope on the screen that contains the signal ( when it exists ) and
rejects the rest as noise.

However, "fast" it would not be.  A PSK31 "bit" lasts for only 31.25 ms.
Tone encoding is out of the question.  Even with OOK, then a 60 Hz video
would be able to stack at most two frames per bit.  Faster video probably
throws out any availability to "amateur".  So that leaves slowing the data
rate down.  We might be talking about VARICODE1 for 1 Baud or VARICODE0.1
for tenth Baud.   Ten seconds per bit would get you 300 frames to stack with
30 FPS video, which opens up the experimentation to anyone that can strap a
webcam to a telescope.  Maybe we should be thinking of adapting JT65 to six
OOK bits instead of PSK31 or RTTY or ASCII............Better prove the
concept of receiving messages from stacked video images with slow
Morse...........................

Fun to think about.

James
 n5gui

----- Original Message -----
From: "Laser @ KatHouse1.com" <laser at kathouse1.com>
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Sent: Friday, September 21, 2007 2:35 PM
Subject: Re: [Laser] Big adaptive optics

> This has also been available to the backyard astronomer for quite a few
> years using a standard video camera and a program called Astrovideo.  I've
> been using the program for quite a few years.  The results are nothing
short
> of spectacular not only for eliminating atmospheric distortion but also
> because it has the ability to stack images and literally pull the image up
> out of the noise.  I can see objects using this setup that I can't even
> begin to see using my eyes and any eyepiece that I own  I can image deep
> space objects from my light polluted front yard by lining the camera up on
> the known starfield around the desired object then let Astrovideo do it's
> magic.  Sometimes in as little as 10 to 15 seconds the desired object will
> start to appear out of the noise.  The program has many different modes
> depending on whether you are trying to enhance signal to noise, eliminate
> atmospheric distortion or both.  The program has both automatic and manual
> modes for stacking images.
>
> http://www.coaa.co.uk/astrovideo.htm
>
> =====
>
> ----- Original Message -----
> From: "J Forster" <jfor at quik.com>
> To: "Free Space LASER Communications" <laser at mailman.qth.net>
> Sent: Wednesday, September 19, 2007 1:52 PM
> Subject: Re: [Laser] Big adaptive optics
>
>
> > This idea has been around on that telescope since at least the 1960s. It
> was first done with movie film as I remember.
> >
> > -John
> >
> >
> >
> > James Whitfield wrote:
> >
> > > I just read an article that was forwarded to me by members of the
> astronomy club about a technique for using adaptive optics on the 200 inch
> Hale telescope on Mount Palomar.  The concept is that the dynamics of the
> atmosphere will cause for brief times on small areas of the image formed
by
> the telescope to have less blurring than the image as a whole or if the
> pixels are integrated for longer times.  The use of a "fast" ( all of 20
> frames per second ) camera is used to capture a succession of images which
> are then searched for these "lucky" patches which are then combined.  I
> thought it was interesting reading.  (  If you are curious, try searching
> for "Palomar" and "Lucky Camera". )
> > >
> > > There might be something that can be adapted to light communication
> experiments at our level.  Maybe use the peak output from an array of 16
> light sensors.  Maybe integrate the light comming to a sensor during a
frame
> then reseting it.  Maybe it is just thinking about the optical system for
an
> image telescope as it contrasts to a communications instrument ( What does
> sharp focus/blurred image mean for a single pixel camera?  Or light
> modulated with a data stream? ).
> > >
> > > Does it spark any ideas for any of you?
> > >
> > > James
> > >  n5gui
> > >
> >
> > _______________________________________________
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> > Laser at mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/laser
>
>
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