SHOALS Mapping of Northern Lake Michigan Trout-Spawning Reefs

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SHOALS Mapping of Northern Lake Michigan Trout-Spawning Reefs

By Peter Barnes and Kristen Lee
October 2001

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The CMGP, Great Lakes Science Center (BRD), U.S. Army Corps of Engineers (USACE), and John E. Chance and Associates combined their efforts to obtain six days (40 flying hours) of SHOALS (Scanning Hydrographic Operational Airborne LIDAR Survey) data in northern Lake Michigan just before the Labor Day weekend.

The SHOALS system, operated jointly by the USACE and U.S. Navy, uses LIDAR (light detection and ranging) to make detailed seafloor and lakebed maps in areas that are too shallow for practical use of sonar systems. Mounted on a small aircraft, the SHOALS system fires a laser into the water, where a small amount of energy from the infrared pulse is reflected off the water surface. The water depth is calculated from the time difference between the infrared surface return and the blue-green bottom return.

study area location map, north of Traverse Bay on the northwestern shore of lower Michigan

Study Area: Location of SHOALS surveys in northern Lake Michigan, August and September 2001. Lake-floor contour lines are in 10-m interval areas, with depths above 30 m in blue. Black boxes show areas of completed LIDAR surveys. Spectrometer sites are shown as red squares.

image of raw SHOALS data of Gull Island Reef
Mapping the Bottom: Preliminary look at unscaled raw SHOALS bathymetry data for Gull Island Reef (see location map above). Depths range from about 3 to 25 m. North is up, and data extend about 7 km north to south.

In the recent Lake Michigan mapping, data were obtained from five reef sites and two coastal sites in the Northern Lake Michigan Trout Refuge and along both populated and unpopulated coastlines (see location map above). The SHOALS data, collected on a 4-m grid, are excellent and consistent to depths in excess of 25 m. Final edited products and data are expected in October. Preliminary data show good bathymetric detail over the reefs of glacial and bedrock outcrops (see example at left).

In addition to providing water depths, the SHOALS data will be used by Jim Gardner and University of New Hampshire colleagues to extract the albedo, or reflectivity, of the lake floor. Albedo can provide information on lakebed geologic and biologic composition. It is calculated from the strength of the return signal after the effects of travel through the lake water have been taken into account. To measure those effects, USGS scientists used a small boat to take spectrometer measurements of the lake water as the SHOALS aircraft collected LIDAR data. Biologist/boat operator Rich Stickel, NAGT (National Association of Geoscience Teachers) summer intern Kristen Lee, and Peter Barnes were dismayed to learn that the SHOALS aircraft can operate in conditions that are very uncomfortable for small-boat work! They found themselves assessing the effectiveness of different combinations of drugs for motion sickness in addition to their scientific work. They also collected grab samples of lakebed sediment, and found that grab samplers dropped on boulders or outcrops in Lake Michigan come up with zebra mussels (in ocean areas, samplers dropped on hard substrate generally come up empty).

After the field effort, Peter attended a second meeting of the Eastern Region interdisciplinary planning project for the Great Lakes Region in Ann Arbor. Participants from Biological Resources Discipline, National Mapping Discipline, Water Resources Discipline and Geologic Discipline focused on nearshore and coastal ecosystem habitat and water (including groundwater) quality and their response to change (in lake level, land use, and so forth) as a region-wide niche for USGS data integration and research efforts.

After collecting spectral data, Kristen explored libraries, interviewed university staff, and read gray literature in Ann Arbor in search of current and past research and digital data. These data will be used to augment the GIS database of geologic and benthic information in the SHOALS survey area.

Scanning Hydrographic Operational Airborne LIDAR Survey (SHOALS)
U.S. Army Corps of Engineers

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October 2001

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in this issue: cover story:
Sea-Level Rise in Nat'l Parks

Collecting Caribbean Dust

Florida Beach Health

Lake Michigan Trout

Watershed Initiative

Blacks in Gov't 2001

Coastal Change Issues

Pacific Congress Service Award—Mike Field

WHFC Employees in 10K

Educating the Public About Coastal Hazards

Author of Organic Geochemistry Novel Visits

October Publications List