Gravity Gradiometry; June 1998; Scientific American Magazine; by Bell; 6 Page(s)

During the cold war, submarine crews from both sides of the iron curtain were faced with the problem of guiding their vessels through the dark reaches of the ocean. Although they could always switch on their sonars to sense obstacles ahead or the depth of water below the keel, that act would send out acoustic signals, loud "pings," which would quickly reveal their presence to enemies-- something right-thinking submariners hesitate to do.

In an effort to devise more stealthy aids to underwater navigation, U. S. and Soviet navies designed sensitive instruments that could measure tiny variations in the pull of gravity caused by underwater ridges or mountains. Yet with the exception of Tom Clancy¿s fictional submarine Red October, no Soviet vessel actually carried such elaborate gear. Only the U. S. ballistic-missile submarines benefited from these sophisticated devices, called gravity gradiometers. This equipment was a well-kept military secret for many years, but now I and other civilian geologists are making use of similar gravity gradiometers to pinpoint the location of oil and gas deposits deep underground.