Sea Floor Topography and Backscatter Intensity of the Historic Area Remediation Site, Offshore New York, USGS OFR 00-503

The purpose of this project is to map the surficial geology of the sea floor of Historic Area Remediation Site (HARS) and changes in surficial characteristics over time. The sea floor of the HARS, approximately 9 square nautical miles in area, is being remediated by placing at least a one-meter of clean dredged material on top of the existing surface sediments that exhibit varying degrees degradation resulting from previous disposal of dredged and other material. This GIS project presents multibeam and other data in a digital format for analysis and display by scientists, policy makers, managers and the general public. Comparison of the topography and backscatter intensity from the three surveys show changes in topography and surficial sediment properties resulting from placement of dredged material in 1996 and 1997 prior to designation of the HARS, as well as placement of material for remediation of the HARS. This study is carried out cooperatively by the U.S. Geological Survey and the U.S. Army Corps of Engineers. This data set includes topography and backscatter intensity of the sea floor of the Historic Area Remediation Site (HARS), located offshore of New York and New Jersey. The data were collected with a multibeam sea floor mapping system on surveys conducted November 23 - December 3, 1996, October 26 - November 11, 1998, and April 6 - 30, 2000. The surveys were conducted using a Simrad EM 1000 multibeam echo sounder mounted aboard the Canadian Hydrographic Service vessel Frederick G. Creed. This multibeam system utilizes 60 electronically aimed receive beams spaced at intervals of 2.5 degrees that insonify a strip of sea floor up to 7.5 times the water depth (swath width of 100 to 200 m within the survey area). The horizontal resolution of the beam on the sea floor is approximately 10% of the water depth (3-5 meters in the survey region). Vertical resolution is approximately 1 percent of the water depth, or 0.3 m. Maps derived from the mulitbeam observations show sea floor topography, shaded relief, and backscatter intensity (a measure of sea floor texture and roughness) at a spatial resolution of 3 m/pixel.