By Sheri McWhirter
TRAVERSE CITY -- Raindrops pelted and roiled scenic West Grand Traverse Bay's surface, but those aboard the Northwestern didn't mind.
They cared more about what undiscovered treasures lurked beneath.
Northwestern Michigan College leads the first effort to map the bottom of Grand Traverse Bay in more than 80 years, and school officials this week used sonar technology to distinguish sand bars, rocky shoals, fish habitat, logs, plant growth and sunken ships.
It's the only Great Lakes locale where such high-resolution, water-mapping technology is used. Officials hope it leads to more efforts to study the floors of North America's freshwater inland seas.
"Our students will use this information for their studies on what's going on in the bay," said Hans VanSumeren, director of NMC's Water Studies Institute. "I think getting people excited about what's down there is important. It's not just about what's on the surface."
Officials are using side-scan sonar equipment on the Northwestern, NMC's research vessel, to capture imagery in a 1,000-foot swath as they move back-and-forth across the bay. The technology allows them to view outlined images from the bottom.
"To be able to tell people about what's in our Great Lakes is wonderful. We've never before seen the lake bottom like this," said Mark Breederland, Michigan Sea Grant's extension educator in Traverse City, and whose agency is assisting with the research.
Existing bay depth data stretches to the late 1920s. Modern sonar technology will provide updated, expanded information that can be used in environmental assessments, coastal management, bottomland studies, commercial navigation charts, fisheries research and tourism opportunities.
Data gathered as part of the research will be shared with agencies like the National Oceanic and Atmospheric Administration and catalogued on a public digital water library, VanSumeren said.
The community college's survey equipment was donated by Kongsberg Underwater Technology, Inc., a Norwegian company.
Officials have worked for a week to map the bay bottom, and captured sonar images of what's believed to be the sunken Lauren Castle tugboat near Suttons Bay. The image shows a boat with mast sticking up in about 400 feet of water, where it sank in November 1980.
"I think she's sitting straight up and down on the bottom," VanSumeren said.
A submersible remote-operated vehicle with a camera will be sent down to investigate further.
The Northwestern on Wednesday slowly cut through the water about a half-mile southwest of Power Island when a blip appeared on the computer screen.
"That's the wreck of the Tramp," VanSumeren said. "It's very sandy, so anything that's on the bottom really stands out."
The Tramp was a wooden, 54-foot tugboat that sank in the 1970s, and now is a popular diving attraction. It appeared on the sonar screen with a white-shaded area next to it, the "shadow" of the sonar image of the vessel.
"It's like the shadow of a tree. You can tell what a tree looks like without actually looking at it," VanSumeren said.
Sonar equipment sends out sound waves on both sides of the Northwestern at a 45-degree angle toward the bay floor. The sonar "shadow" was created as sound waves bounced back from the sunken tugboat.
The sonar even picked up schools of whitefish that appeared on the computer screen as clusters between the bottom and the bay's surface.
"How can you not be fascinated by this? This is awesome," said Jack Rowell, of Kalkaska, a potential NMC student.
Rowell was along for the ride on Wednesday to get a taste of NMC's freshwater studies as he tries to decide between that program and the college's Great Lakes Maritime Academy.
Rowell was laid off from a machining job in Kalkaska and wants to complete training to find a new career.
"I'm definitely interested in this. I'm interested mostly in getting a job," he said.