How do satellite images provide us with quantitative estimates for environmental changes?

Question

How do satellite images provide us with quantitative estimates for environmental changes?

Answer 1

Over a longer period of time and with refined methods of data collection,  they will be able to see hot and cold spots as well as drought and rainy trends..

Answer 2

As whiskers said, by giving us a big picture look at the earth.  An example would be the amount of deforestation occurring.  With before and after shots of logged areas you could come up with a figure to tell you the area that's been logged.

Answer 3

A few sites to check out that answer this question pretty well, I believe.