#1 Woods Hole and Oysters ... Oysters are shallow-water, coastal filter feeders. They are a significant economic resource and a major environmental bellwether. Oyster beds provide protection from hurricanes and prevent coastal erosion. As all mariners know, navigating near oyster shoals is hazardous and to be avoided whenever possible. The Woods Hole Science Center purchased an SRI USV to collect extremely sophisticated data for a major scientific study in hazardous, shallow water environments.

NS31B-1574: Advances in Shallow-Water, High-Resolution Sea Floor Mapping: Integrating an Autonomous Surface Vessel (ASV) into Nearshore Geophysical Studies by Denny, J.F., O’Brien, T.F., Bergeron, E., Twichell, D., Worley, C.R., Danforth, W.W., Andrews, B.D., and Irwin, B.

U.S. Geological Survey, Woods Hole Science Center, Woods Hole, MA [Study Excerpts follow ...]

The U.S. Geological Survey (USGS) has been heavily involved in geological mapping of the sea floor since the 1970s. Early mapping efforts such as GLORIA providedbroad-scale imagery of deep waters (depths > 400 meters) within the Exclusive Economic Zone (EEZ). In the early 1990s, the USGS research emphasis shifted from deep- to shallow-water environments (inner continental shelf, nearshore, estuaries) to address pertinent coastal issues such as erosion, sediment availability, sediment transport, vulnerability of coastal areas to natural and anthropogenic hazards, and resource management. Geologic framework mapping in these shallow-water environments has provided valuable data used to 1) define modern sediment distribution and thickness, 2) determine underlying stratigraphic and structural controls on shoreline behavior, and 3) enable onshore-to-offshore geologic mapping within the coastal zone when coupled with subaerial techniques such as GPR and topographic LIDAR.

Research in nearshore areas presents technological challenges due to the dynamics of the environment, high volume of data collected, and the geophysical limitations of operating in very shallow water. In 2004, the USGS, in collaboration with NOAA’s Coastal Services Center, began a multi-year sea floor mapping effort to better define oyster habitats within Apalachicola Bay, Florida, a shallow water estuary along the northern Gulf of Mexico. The bay poses a technological challenge due to its shallow depths (< 5-m) and high turbidity that prohibits the use of bathymetric LIDAR. To address this extreme shallow water setting, the USGS incorporated an Autonomous Surface Vessel (ASV) into sea floor mapping operations, in June 2006. The ASV is configured with a chirp sub-bottom profiler (4-24 kHz), dual-frequency chirp sidescan-sonar (100/400 kHz), single-beam echosounder (235 kHz), and pan and tilt digital camera, and has been used to delineate the distribution and thickness of surficial sediment, presence of oyster beds, and sea bed morphology in water depths of 1-5 m.

The ASV is a catamaran-based platform, 3 meters in length, 1-2 meters in width, and approximately 260 lbs in weight. The vehicle is operated remotely through a wireless 802.11b network enabling real-time monitoring of data acquisition. The ASV is navigated using DGPS/RTK, and heave, pitch, roll and heading are recorded from onboard motion sensors. Additional sensors, such as ADCPs, can also be housed within the vehicle. The ASV is able to operate in previously inaccessible areas, and will not only augment existing shallow-water research capabilities, but will also improve our understanding of the geologic controls to modern beach behavior and coastal evolution.