[meteorite-list] Sand Dunes and Meteorites

[Matson, Robert]

Title: Message

On the subject of remote sensing of meteorites from above, Jim Hartman wrote:   > I know that I am not the rocket scientist here & this may be an oversimplified  > theory but I have a picture of my house & my fathers house taken from a  > satellite in orbit. Now I may be wrong but I kinda think that if someone is  > going to go to the trouble of putting millions of dollars of equipment into  > orbit that they would include thermal imaging as part of that inventory.    Rocket scientist chiming in:  many thermal imaging sensors are currently in orbit (e.g. Landsat, EOS, Spot).  But the trouble with all of them is insufficient resolution.  Even if you could get 2-meter resolution data in a waveband of interest, a meteorite with a 10-cm x 10-cm "footprint" would only fill one 400th of a pixel.  In order to detect such a meteorite with a signal-to-clutter ratio of 3:1, the difference between your target radiance and background radiance would need to be 800 times the standard deviation of the scene gradient.  It's not completely impossible, but you're going to need a very benign background and a significant emissivity difference between the background and the meteorite.   Temperature difference ends up buying you very little in this case because the target represents such a small fraction of the area of a pixel.  For instance, to double the radiance output of a 300 K object in the 3-5 micron band, you'd need to increase its temperature to 320 K -- 36 deg F warmer.   What this all boils down to is that you need a sensor flying at low altitude in order to get the footprint size down to something more comparable to the size of the meteorites you expect to find... --Rob