Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!munnari.oz.au!uniwa!vax7!tgumleyle
From: Gumley_LE@cc.curtin.edu.au (Liam Gumley)
Newsgroups: sci.space
Subject: Re: Spy satellite coverage of the Gulf
Message-ID: <7000.27b11bd8@cc.curtin.edu.au>
Date: 7 Feb 91 01:20:23 GMT
References: <14230@ganymede.inmos.co.uk> <4409@syma.sussex.ac.uk>
Organization: Curtin University of Technology
Lines: 44

In article <4409@syma.sussex.ac.uk>, nickw@syma.sussex.ac.uk (Nick Watkins) writes:
> From article <14230@ganymede.inmos.co.uk>, by conor@lion.inmos.co.uk (Conor O'Neill):
>> I realise that the real details are almost certainly classified, but I would
>> like to get some feel for the answers:
>> 5) Are they affected by the dark, or by cloud cover, or is much of the
>> sensing done in the Infra Red?
> Radar isn't, apparently, I think IR will be affected by cloud cover
> though. Maybe somebody who knows about weather satellites can help.

Nothing classified here....

Visible sensors obviously only work during the daytime.  Depending on the
type of orbit, the satellite can be in sunlight for up to about 50% of the
time (sun-synchronous orbit).  I don't know the altitude of the KH-11, but
I imagine it would be low, to maximise image spatial resolution.  This
probably means it does not have a sun-synchronous orbit.  They are usually at
an altitude of 850 km or so.

Infrared sensors are usable both in the day and the night, although if you
want to see targets such as vehicles or people, you would want to do it at
night when the ground is cooler than the objects you are trying to see.
Weather sensors have a different kind of emphasis than an recon imaging system
would have.  Meteorologists are typically more concerned about knowing the
temperature of a given pixel accurately, rather than the spatial resolution
of that pixel.

Most kinds of clouds are either partly or completely opaque to both
visible and infrared radiation - you can't see the ground through them.

I don't know too much about radar, but at microwave wavelengths, clouds are
pretty transparent.  I imagine that synthetic aperture radar (SAR) technology
would be used.  Oceanographic SAR aims for height resolution on the scale
of centimeters, so you can imagine the resolution defense sensors would be
working at.

Check out "Jane's all the world's satellites" - a pretty good reference.

Cheers,
Liam.

-- 
tgumleyle@cc.curtin.edu.au
#Liam E. Gumley, Department of Applied Physics, Curtin University of Technology#
#Perth, Western Australia.   >>>All opinions expressed are exclusively mine.<<<#