Snooping on the Sound of Sediment
By Hank Becker
April 4, 1997
New state-of-the art acoustic
technology is uncovering the secrets of soil--undisturbed in the field or
moving in streams.
Scientists with USDAs
Agricultural Research Service have
teamed up with the University of
Mississippis National Center for
Physical Acoustics at Oxford, Miss., to develop a new probe microphone that
can provide clues about physical characteristicssuch as air spaces in the
soilwithout disturbing the soil and wrecking its natural profile in the
The key, the scientists say, is how well the soil absorbs sound waves.
Theyve developed a procedure that lets them quickly and accurately
measure absorption of sound waves penetrating up to 4 inches deep in the upper
soil profile. The technology also could be used to monitor the moisture content
in fields so automated sprinkler systems would turn on only when the soil needs
The scientists say acoustic technology can also help determine sediment
concentrations in flowing water. That information could be useful in devising
strategies to protect streambeds from filling up with sediment, which can cause
flooding, erosion or collapse of the stream banks. Such information is critical
for developing stable channels in agricultural watersheds.
The researchers are using a sonar device called a SedBed Monitor to track
sediment movement in streambeds. Sound that bounces off sediment moving along
the stream bottom is picked up by a microphone and fed into a computer. Within
minutes, the computer can display or print out a graphic image of the changing
topography of the streambed.
Scientific contact: Mathias J.
Sedimentation Laboratory, Oxford, Miss., phone (601) 232-2927, fax (601)