Aren't these cameras dependent on the lighting conditions? Unless you get sufficient contrast the amount of computing to minimize these points is quite big.

Didn't they try thermal imaging? The new cryocooled infra red cameras cool their sensors to -40 centigrade which makes them very sensitive.

So we could measure the infrared heat signatures of trees and map them out.

I haven't tried this. I'm thinking each species of trees will show enough uniqueness in their heat signatures to be able to identify them.