Xref: utzoo sci.space:4120 sci.crypt:716
Path: utzoo!linus!husc6!bloom-beacon!athena.mit.edu!jfc
From: jfc@athena.mit.edu (John F Carr)
Newsgroups: sci.space,sci.crypt
Subject: Re: satellites
Keywords: resolution
Message-ID: <2209@bloom-beacon.MIT.EDU>
Date: 10 Jan 88 02:02:42 GMT
References: <873@uop.edu> <2166@umd5.umd.edu> <4910@well.UUCP> <1952@netsys.UUCP>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: jfc@athena.mit.edu (John F Carr)
Organization: Massachusetts Institute of Technology
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In article <1952@netsys.UUCP> wb8foz@netsys.UUCP (David Lesher) writes:
>>>? "Satellite saw Waite, newspaper says"

>>>Uh-huh.... apply NaCl liberally..

>On the other hand, several public sources have reported that
>resolutions good enough to read the brand of coffin nails
>being smoked by the guard on duty in Moscow are in use. 
>If you combine that with the art of *interpretation*, 
>it is not unreasonable that the
>distinctive, big bulky fellow walking outside the isolated house 
>in a area of interest, surrounded by guards with AK-47s is 
>Terry Waite. I suggest the book "Deep Black" 
>on the subject of remote imagery.


I haven't read the book, but there is a simple argument against
such resolution.  Cameras in orbit are limited either by diffraction
or atmospheric conditions.  A telescope at sea level, in perfect 
weather, is typically limited to no better than 1" (that is a unit 
of angle: 1 arc-second, not 1 inch).  At 200 km this is a linear 
distance of 1 meter.  I would believe that looking down 
from orbit would give a different result (though I don't know).  
An *absolute* limit on the resolution of an image is diffraction 
in the camera.  For visible light (wavelength 5 X 10^-7 m), and a 
1 meter lens or mirror on the satellite, the limit is about 10 cm.  
To distinguish an object of size 1 cm, a 10 meter lens/mirror would 
be needed.  The Space Telescope, which has not been launched and is 
to my knowledge the largest mirror in or intended to be in space, is 
about 2 meters.  The biggest telescope in the world is 6 meters.  
There are techniques for processing images distorted by the 
atmosphere or an imperfect lens, but they can not get an image to be 
better than the diffraction limit.

I would be impressed if any intelligence agency could regularly scan
a city at 4 inch resolution while also doing its other (presumably 
more important) business.  (assuming B+W image, 256 intesity levels,
10 cm pixels, 2 km square area : 400 MB per image.)  Unless the miltary
or intelligence agencies are far ahead of anything I have read about in
computer pattern recognition (or somehow learned exactly where to look),
I would not believe the report "Satellite saw Waite".  (Unless someone
was *extremely* lucky).

  --John Carr