DNR Researchers Use Low-cost Sonar to Map Stream Habitat

It’s a question every researcher who studies fish or other aquatic life eventually faces:

What exactly is beneath the surface of that murky stream?

Or as DNR aquatic resources biologist Adam Kaeser said, talking about detailed landscape maps, “Once you get to the edge of the water … you come to the edge of the information.”

Not for long. That lack of information is giving way to advances Kaeser and DNR GIS specialist Thom Litts have made translating imagery from a blue-collar, side-imaging sonar unit into a GIS layer that probes the underwater side of streams.

Kaeser and Litts have published their findings in American Fisheries Society journals (December 2008 and April 2010), trained some 200 people in using the sonar and scaled their methods to suit the most common level of ArcGIS. They are also providing software tools needed to process the sonar imagery for free. Results from the habitat mapping initiative offer biologists with limited training a low-cost, relatively fast way to document wood, substrate and other habitat in navigable streams.

“It would be extremely difficult to map large, muddy streams any other way,” Litts said. “I think we’ll see some good things come of this.”

The side-scan sonar method is already being used to explore habitat preferences of state-listed Barbour’s map turtles in southwest Georgia’s Ichawaynochaway Creek, search out spawning sites for the rare robust redhorse in the Ocmulgee River and study habitat relationships between three bass species in the upper Flint River. For the Auburn University bass study on the Flint, Kaeser and Litts covered nearly 15 miles of river in one day and produced the map in a week. Traditional methods – measuring habitat along transects and extrapolating findings to the entire area – would have taken several weeks, or longer.

Using side-scan sonar was once the realm of deep-water marine research with tow-behind-the-boat units worth tens of thousands of dollars. But Litts and Kaeser use a Humminbird 900-series Side Imaging system priced at less than $2,000. They motor along the middle of a stream at 5 mph, taking depth readings and sonar “snapshots” that reach from bank to bank.

Computer programs piece together the digital images, a process Litts wrote tools for and smoothed out the remaining kinks. It takes time to interpret the imagery, which looks like a moonscape, with boulders as bumps and logs as lines. Accuracy is confirmed through field spot-checks. The images taken by sound instead of light are rich in detail.

“We’re on our third or fourth generation of refinement,” Litts said.

But they are definitely on to something.

Kaeser envisions a biologist on a blackwater stream pulling up the data on his smartphone. “I think you’re going to see an explosion” in use, Kaeser said.

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