These data are benthic study GIS shapefiles (.shp, .shx, .prj) with associated .dbf attribute tables and specific Federal Geographic Data Committee metadata. A generalized browse graphic was generated at the NODC and included with these data.

The Coastal Change Analysis Program (C-CAP) at the NOAA Office for Coastal Management (formerly the Coastal Services Center) partnered with the Massachusetts Department of Environmental Protection Wetlands Conservancy Program (DEP-WCP) and Office of Coastal Zone Management (CZM) to produce a digital coverage of submerged aquatic vegetation, primarily eelgrass (Zostera marina) along the Atlantic coast of Massachusetts. Conventional color metric aerial photography at a scale of 1:20,000 was acquired from 1994-1996 according to stringent parameters detailed in the C-CAP protocol (www.csc.noaa.gov/ccap). The photography was photointerpreted by DEP-WCP using a biocular stereoscope (Cartographic Engineering Modular Stereoscope Model SB 190). Polygons of eelgrass were delineated onto acetate overlays affixed to each photograph.

Extensive fieldwork was conducted to develop signatures and gather surface level data where the presence or extent of habitat was not apparent from the photography. An underwater video camera was utilized in this effort. The aerial photos, with the interpreted acetates attached, were scanned using a photogrammetric quality scanner (AGFA Horizon Plus) at a resolution of 600 dpi resulting in a pixel resolution of .85 meters. The resulting image file was rectified (bilinear 2nd order) by C-CAP to 1 meter black and white and color digital orthophotos supplied by CZM. The polygon delineation from the rectified image was then digitized onscreen. In addition, a point file was generated based on field-verified sites as well as all occurrences of widgeon grass (Ruppia maritima) and algae.

The rectification and digitization was completed utilizing the ERDAS Imagine software package. The benthic data is classified according to the System for Classification of Habitats in Estuarine and Marine Environments (SCHEME). This system is fully described in Development of a System for Classification of Habitats in Estuarine and Marine Environments (SCHEME) for Florida, Report to U.S. EPA - Gulf of Mexico Program, Florida Fish and Wildlife Conservation Commission, Florida Marine Research Institute. Review Draft 12/04/02. The polygon vector coverage was accuracy assessed by C-CAP and DEP-WCP in July 1997 and September 1998. The assessment was based on random points generated within the polygon boundaries. Navigation to each point in the field was accomplished using real time differential GPS. The underwater video camera was used to verify the presence of the mapped feature at the random point. The accuracy of the mapped grass was 85.4 percent (175 of 205 sites mapped correct).