International treaties. Comprehensive test ban: the long road.

Watching the waves IMS also has a smaller network of sensors to listen for explosions carried out underwater, just above the ocean surface, or below the ocean bottom. Sound travels very efficiently in water: Kiyoshi Suyehiro of the Institute for Research on Earth Evolution in Kanagawa, Japan, says a 20-kilogram test charge of TNT was detected 16,000 kilometers away. As a result, IMS has just 11 hydroacoustic stations positioned around the vast expanses of the Atlantic, Pacific, and Indian Oceans in the Southern Hemisphere. Sound propagates in deep water especially well at a depth of about 1000 meters in what is known as the sound fixing and ranging (SOFAR) channel. Six of the IMS’s hydroacoustic stations consist of SOFAR hydrophones in deep water as much as 100 kilometers from the coast of remote islands. Each is a set of three hydrophones anchored to the seabed and connected to shore-based stations by cable. In addition to hydrophones, IMS has five stations to detect T-phase waves, the third or tertiary waves, after P and S, from a seismic tremor. These seismic stations pick up waves that have traveled into the ocean as hydroacoustic waves and then back into the ground. To get the best results, such stations need to be sited near coasts or on small islands. Researchers here were enthusiastic about the scientific spinoff of the hydroacoustic net-