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posted by martyb on Monday December 03 2018, @06:20AM   Printer-friendly
from the I-see^W-hear-what-ytou-did-there dept.

Revealing hidden information in sound waves

“Acoustic fields are unexpectedly richer in information than is typically thought,” said David Dowling, a professor in U-M’s Department of Mechanical Engineering.

[...] Sonar arrays are typically designed to record sounds in specific frequency ranges. Sounds with frequencies higher than an array’s intended range may confuse the system; it might be able to detect the presence of an important contact but still be unable to locate it.

Any time sound is recorded, a microphone takes the role of the human ear, sensing sound amplitude as it in varies in time. Through a mathematical calculation known as a Fourier transform, sound amplitude versus time can be converted to sound amplitude versus frequency.

With the recorded sound translated into frequencies, Dowling puts his technique to use. He mathematically combines any two frequencies within the signal’s recorded frequency range, to reveal information outside that range at a new, third frequency that is the sum or difference of the two input frequencies.

“This information at the third frequency is something that we haven’t traditionally had before,” he said.

In the case of a Navy vessel’s sonar array, that additional information could allow an adversary’s ship or underwater asset to be reliably located from farther away or with recording equipment that was not designed to receive the recorded signal. In particular, tracking the distance and depth of an adversary from hundreds of miles away—far beyond the horizon—might be possible.

And what’s good for the Navy may also be good for medical professionals investigating areas of the body that are hardest to reach, such as inside the skull. Similarly, remote seismic surveys that parse through the earth seeking oil or mineral deposits could also be improved.

[...] More information:


Original Submission

 
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