> However, I recently thought about the fact that taking a picture from > the ground looking up shouldn't be any different than taking a picture from > orbit looking down. In fact, the situations are not the same. The local variations in atmospheric density that cause degraded resolution are much closer to the ground than they are to objects in space, and therefore the "lever arms" over which they operate in blurring images are much different. You can see this effect by using a piece of pebble glass -- shower doors are often made of pebble glass -- to simulate the turbulent atmosphere: Place a newspaper two meters from the door and stand on the opposite side of the door with your eye close to the glass; the print on the paper will appear greatly blurred. Now move the paper so that it is close to or in contact with the glass and back away so you are viewing the paper from two meters distance -- at least the headlines will be readable. The first case corresponds to looking into space from the ground, the second to looking at the ground from space. > If satellites can resolve things smaller than a meter > across then with good optical equipment, we should be able to do the same > when looking at the satellite. We can, using a variety of tricks to avoid or compensate for the atmospheric blurring. Short-exposure imaging, speckle imaging, adaptive optics, laser guide stars are terms to seach for. ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Sat Dec 30 2000 - 06:55:26 PST