5 meter ArcRaster grid of hillshaded bathymetry data collected in Buzzards Bay by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration offshore of Massachusetts in 2004, 2009, 2010, and 2011 (BB_hlshd5m, UTM Zone 19N, Esri BINARY GRID)

Hydrographic survey H11319: Horizontal sounding positional control for the NOAA H11319 survey was determined using the Global Positioning System (GPS) corrected by U.S. Coast Guard Differential GPS (DGPS) beacon stations. The primary DGPS beacon used for survey H11319 was at Acushnet, MA and the secondary beacon was at Portsmouth, NH. No horizontal control stations were established for the NOAA survey. Additional information may be found in the NOAA Descriptive Report for survey H11319 and the Data Acquisition and Processing Report. Field activities 2009-002-FA and 2010-004-FA: Navigation was acquired with a Coda Octopus F180 Differential Global Positioning System + Wide Area Augmentation System (DGPS+WAAS), which is accurate to + or - 1 to 2 meters, horizontally. All DGPS data are referenced to WGS84. The SWATHPlus transducers were mounted on a rigid pole, approximately 2.46 m below the water line, along the starboard side of the M/V Megan T. Miller. The DGPS antenna was located on the same pole approximately 4.3m above the sea surface. These offsets were corrected within the SWATHPlus acquisition software. Field activity 2011-004-FA: Navigation was acquired with a Coda Octopus F180 Differential Global Positioning System + Wide Area Augmentation System (DGPS+WAAS), which is accurate to + or - 1 to 2 meters, horizontally. All DGPS data are referenced to WGS84. The SWATHPlus transducers were mounted on a rigid pole, approximately 2.17 m below the water line, along the port side of the M/V Scarlett Isabella. The DGPS antenna was located on the same pole approximately 4.6m above the sea surface. These offsets were corrected within the SWATHPlus acquisition software. The DGPS horizontal positional accuracy is estimated to be within 3-5 m; WAAS enabled DGPS accuracy is estimated to be within less than 3 m and the accuracy of RTK-GPS (which was not applied to the horizontal positions for these surveys) is estimated to be less than 1 m. However, the U.S. Coast Guard maintains a maritime DGPS service providing 10 meter accuracy for the coastal areas of the continental US; therefore, a very conservative, worse-case estimate of the horizontal positional accuracy of this survey data is approximately 10 meters (although these systems have been shown to be reliable to less than 2m). (sources: http://www.noaa.gov; http://www.nos.noaa.gov; http://www.ngs.noaa.gov; http://www.nstb.tc.faa.gov/; http://www.navcen.uscg.gov).