[Beowulf] Re: blackbox on Mars?

Jim Lux James.P.Lux at jpl.nasa.gov
Mon Oct 30 09:44:18 EST 2006


At 06:32 AM 10/30/2006, Jim Lux wrote:
>At 12:45 AM 10/30/2006, Jakob Oestergaard wrote:
>>On Fri, Oct 20, 2006 at 04:21:31PM -0400, Robert G. Brown wrote:
>>...
>>...
>> > geosync on Earth, and if the military and weather programs have given us
>> > nothing else, they've given us simply gangbusters orbital cameras.  I
>> > mean who on this list hasn't gone on Google Earth yet?  Through EARTH's
>> > atmosphere and from EARTH orbit you can see my house here:
>> >
>> >   35^\circ 59' 17.10"N
>> >   78^\circ 58' 50.22"W
>> >
>> > At 512 feet you can clearly make out my Ford Excursion in the driveway,
>> > see the row of cypruses along the back, see the white table on my back
>> > deck that is about 4' across, see an azalea bush out front (next to the
>> > sidewalk) that is about 1.5' across.  And this isn't the world's best
>> > camera or as high resolution as they could manage, even through Earth's
>> > soupy atmosphere.
>>
>>Mmm... Except... The high res images are from a plane because you can't
>>really make out the fine details from a satellite through the earth's
>>atmosphere.

It's true that most of the Google Earth images are aerial photos, but
I would imagine that one can get 10s of centimeter resolution from 
orbit on Earth (assuming that clouds aren't in the way).   An old 
surveillance satellite (Corona) was doing better than 2 meter 
resolution in the 1970s.

You can fairly easily calculate how big the telescope needs to be so 
that diffraction limiting isn't an issue (it's not big, in this era 
of 10,000kg plus spacecraft).  After that it's a matter of suitable 
image processing to back-out the atmospheric distortions (something 
that, oddly, a Beowulf would work nicely for.. being a EP sort of problem).




>>If you look closely at the houses or trees, you will see that the
>>imagery at the fine detail level is very far from orthographic. Some
>>trees and houses are clearly photographed from their southern side, some
>>from the northern. For example, your house has a visible north-western
>>side, while your south-eastern neighbor has a visible south-eastern side
>>on his house.  The combination of the two images (from two different
>>passes of the plane) is seamless, but the change of perspective is very
>>noticable once you notice  :)

Much satellite reconnaissance these days is done with oblique 
incidence. With very high resolution comes small coverage area, and 
the spacecraft might not be in the right place at the right time, so 
they can point the camera appropriately. This is also useful for 
making topographic maps by shooting stereo pairs.


Jim 


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