You cant detect that from 100 miles up unless you're observing Armageddonlike amounts of the stuff, to my knowledge, anyway. (basic law of physics: strength of radiation drops 4 times when doubling the distance, so distance going from 1 mile to 64 miles doubles 6 times. So radiation would go 1000, 250, 62.5, 15.6, 3.9, 0.97.) The NEST teams in the US drive around in trucks looking for signatures, though they probably have boats and aircraft as well.