As far as i remember, there is an easier way to determine bomb yield, which works at least for bombs which are mostly fission: take a sample from a cloud using the aircraft or a balloon, determine a ratio of original fissile material vs some primary fission product, then knowing time passed since explosion calculate fraction of the material that have reacted, and knowing ideal yield per kilo and amount of material in the bomb, calculate precise yield. For boosted fission the fusion portion of yield is insignificant, and also the fusion is nearly 100% complete, so this is easy to factor in, and in some cases even OK to ignore.<p>Of course if most of the yield was fusion this is a different story.