With the first nuclear bomb, it was easy to find. Wait for the double
flash of blinding light and searing heat to pass, then watch for the rising
fireball. With a pair of binoculars, start at the crown of the expanding
mushroom cloud, then follow the stalk down to where it touches the ground.
Bingo. That's where the nuclear bomb was detonated.
These days, though, there is more to detection than spotting mile-high
mushroom clouds. Despite their power, bombs can be evasively muffled in
underground caves, or masked by synchronizing them with scheduled mining
blasts. Rogue nations who get hold of bombs can test them at sea in international
waters, miles from the nearest detector. Sensors have to be sensitive enough
to detect the blasts from these distances, through air, water, rock, and
soil, yet distinguish them from a constant background of earthquakes, volcano
eruptions, meteor crashes, and mining activity. And they have to do it now.