On Sat, Apr 19, 2014 at 10:44:50AM -0700, jim bell wrote: > [I didn't get a bounce off of CP the first time] > > From: "[email protected]" <[email protected]> > > | It may be possible, in the not-so-distant-future, to record > | people in ultra high definition from a mile away, but the > | 'technology' can be rendered rather useless with somthing > | like...this > | > | http://ramitia.files.wordpress.com/2010/02/japan-face-masks.jpg > | > > > >At this time, it is possible to do facial recognition at 500 meters, > >iris recognition at 50 meters, and heartbeat recognition at 5 meters. > >A newspaper open on a table can be read from orbit. > > I strongly doubt the part about reading the newspaper from orbit. I don't > doubt that the pattern of text and pictures on the front page could be > identified from orbit. ('Identifying the difference between Pravda and > Izvestia'.) An approximation I once heard is that a lens or mirror of about > 4.5 inch in diameter can resolve an angle of one arc-second. A mirror of the > size of the Hubble Space Telescope (which I assume approximates that of the > typical spy satellite today) is about 20x larger, so the resolution should be > 20x better, or 1/20 arc-second. That's 1/(57 degrees per > radian)(3600arcseconds per degree)(20) = 1/4,100,000 radian. From an > altitude of 500 kilometers, that's about 1/8 of a meter, or 120 millimeter. > Maybe that's a pixel-pair, but it's far too large to resolve the text on a > newspaper. > > The best prospect to improve on this resolution would be to use a > 'multiple-mirror-telescope' technology. Light-gathering capability isn't > important in this application; high resolution is. Making a spy-telescope > out of a few different mirrors, held precisely many meters apart, could > conceivable achieve resolutions substantially greater than this. > Jim Bell
Such a mirror array would at some point reflect enough light at odd angles to be visible with the naked eye. I find it more likely that multiple-mirror-telescope tech would be implemented with a swarm of small satellites and extremely precise location tracking and a lot of signal processing later on.
