"SONAR: advance could improve underwater detection"
An advance in sonar technology may soon enable standard sonar equipment to more accurately detect and map underwater artifacts such as mines, even when they are buried. The technique works by rendering the ocean floor transparent, thereby making the artifact stand out in stark relief even if it is buried. The key is time-reversing the echo from a first sonar ping and broadcasting it in lieu of a second sonar ping. The subsequent echo from the second broadcast has its background cancelled out, according to Pierson, effectively rendering the ocean floor transparent. After several such cycles, even the faintest echos from buried mines, once masked by obstacles, stand out on a grid of the ocean floor.
Audio Interviews / Text: http://www.eetimes.com/story/OEG20040304S0021