Murky water is an excellent cloak, masking underwater features and objects from view. Sound can pierce straight through the murk by traveling around suspended particles in the water with minimal scattering. But sound's penetrating ability, thanks to its relatively long wavelengths, also means that it is difficult to "see" underwater objects in any detail. Scientists are currently developing a new sonar technique that can image objects only a few inches in size.
For more than a hundred years, scientists have used sonar (SOund Navigation And Ranging) to pierce underwater depths, but the most common technique, called side-scan sonar, works best on very large objects like shipwrecks or the contours of the ocean floor.
|Image of the shipwreck "Aid" in Estonia using side-scan sonar. |
Credit: Subzone OÜ via Wikimedia Commons
In this method, a sonar device emits pulses of sound (or "pings") as it scans over an underwater area and listens for the echo of the sound reflecting off objects. The time it takes the echo to arrive determines how far away the object is. The frequency of sound used in side-scan sonar can be very high, around 500 kHz (the highest frequency humans can hear is about 20 kHz).
|A sonar device emits sound and listens for the echo off nearby objects.|
Credit: Georg Wiora via Wikimedia Commons
"Our hope is that we can provide tools for studying the underwater environment, which is notoriously difficult," said Plotnick, lead author on the work.
|The cylinder is suspended in a tank of fresh water and slowly |
rotated as the sonar device listens for echoes.
Credit: Daniel Plotnick, Marston Research Group, Washington State University
|The sonar image of a small metal cylinder imaged with sound frequencies between 100 and 700 kHz.|
Image courtesy of Daniel Plotnick, Marston Research Group, Washington State University.
For the moment, the researchers are continuing to test their technique in the lab, in collaboration with researchers at the University of Washington. According to Plotnick, real world oceans will add an extra challenge because of their changing temperatures, currents, and salinity.
In the future, Plotnick suggested this high-resolution sonar can help environmental cleanup efforts around military sites. "Sonar offers a potential tool in locating objects for cleanup. ... if the water is murky you cannot do this by eyes alone."
Further reading:Daniel Plotnick and Philip Marston have published their work in the Journal of the Acoustical Society of America.
By Tamela Maciel, also known as "pendulum"