Snooping on the Sound of Sediment

New state-of-the art acoustic technology is uncovering the secrets of soil--undisturbed in the field or moving in streams.

Scientists with USDA’s Agricultural Research Service have teamed up with the University of Mississippi’s National Center for Physical Acoustics at Oxford, Miss., to develop a new probe microphone that can provide clues about physical characteristics—such as air spaces in the soil—without disturbing the soil and wrecking its natural profile in the process.

The key, the scientists say, is how well the soil absorbs sound waves. They’ve 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 watering.

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. Romkens, USDA-ARS National Sedimentation Laboratory, Oxford, Miss., phone (601) 232-2927, fax (601) 232-2915, romkens@sedlab.olemiss.edu.