Projects & Programs
Eelgrass Mapping in Puget Sound, Washington, Using Underwater Videography and Hyperspectral Imaging
The Washington State Department of Transportation is preparing a plan to repair and replace portions of the Hood Canal Bridge, a vital transportation link for the Northern Olympic Peninsula. Construction activities are expected to have immediate and direct impacts on local marine resources, while facets of the replacement structure may cause chronic, indirect impacts. Preliminary characterization of marine habitats and resources in the region is important so managers and decision-makers may best assess likely impacts to important biological resources such as eelgrass (Zostera marina), geoduck clams (Panopea abrupta) and rockfish species (e.g., Sebastes spp.). This knowledge will facilitate minimization and/or avoidance of impacts to marine nearshore habitats and the environment.
Approach Eelgrass (Zostera marina) habitat in the Northwest has been difficult to delineate and map. However, underwater videography coupled with airborne remote sensing imagery provides a means of producing very accurate, high-resolution maps. The intertidal eelgrass habitat was evaluated and mapped using the Compact Airborne Spectrographic Imager (CASI). The subtidal benthic resource assessment was conducted using underwater video. Assessed resources included eelgrass habitat, substrate type, macroalgae, macroinvertebrates and fish. The eelgrass data were merged with the CASI hyperspectral data to create one layer of intertidal/subtidal coverage. Other benthic resource data were also represented in a spatially geo-referenced context. In addition, resource surveys were conducted in both subtidal areas, using scuba divers, and in intertidal areas, on foot, during extreme low tides. Geographic Information System technology was used to facilitate merging the various multi-scaled datasets.
Advantages
- The hyperspectral image provides broad, detailed intertidal coverage
- The video data provide a more refined classification of eelgrass coverage
- The video data include subtidal coverage
- Comparison of the two datasets provides a means to evaluate the spatial accuracy of the CASI hyperspectral delineation of eelgrass
- The video data provide supplemental information on other resources (fish and macroinvertebrates).
Conclusions/Benefit to Sponsor Merging of the intertidal-subtidal datasets is the first integrated mapping effort using CASI hyperspectral data and underwater video data. In addition, the information gained by the diver surveys and resource surveys completed the data needs. This detailed portrayal of nearshore resources provided the client with critical information for developing a plan for repair and replacement of this vital transportation link.