PORTLAND, Ore. 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.
"Our results are from simulations, but they show that some relatively simple changes to standard sonar equipment will result in a much simpler and effective means of detecting underwater mines," said David Pierson, a scientist at Johns Hopkins University who invented the technique for his dissertation at North Carolina State University.
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.
"Each time we transmit a time-reversed echo, we find the seafloor gets suppressed, but the echo from buried objects are enhanced even when the signal from the buried object was too small to be detected at first," said Pierson. "Today, navies use everything from dolphins to divers to software modeling with elaborate sonar arrays. Now we think we can do better."
The Navy has long sought methods of detecting mines from a distance. The most sophisticated sonar equipment uses multiple transmitters and receivers to map the ocean floor. Pierson's method simplifies this by requiring only a single sonar rig, rather than multiple transmitters and receivers. It could eventually be used to detects buried mines undetected by elaborate multiple tranceiver rigs.
"We don't need arrays of sonar transmitters and receivers or any modeling software. Instead, we just record the return echo of a sonar transceiver, time-reverse it and transmit it back out," said Pierson.
This is not the first time the technique has been used, but it is the first time a reversed broadcast has been used for mapping. Both optical and acoustical experiments have been performed using reversed broadcasts, according to Pierson, but his is the first use isolating targets in backscattered signals.
Pierson's work at North Carolina State University was supported by a grant from the Office of Naval Research and at Johns Hopkins University by the U.S. Navy.