This data is the boundary polygon for the high-resolution bathymetric measurements of the seafloor from Boston Harbor and the harbor approaches, Massachusetts. Approximately 170 km² of sidescan sonar and bathymetric data were collected by the National Oceanic and Atmospheric Administration (NOAA) Ship Whiting in 2000 and 2001 and reprocessed and gridded by the Massachusetts Office of Coastal Zone Management (CZM) and the U.S. Geological Survey (USGS).

The geophysical dataset were collected by the National Oceanic and Atmospheric Administration (NOAA) National Ocean Service (NOS) branch as part of their periodic hydrographic mapping for nautical charting. The raw datasets were provided by NOAA to the Massachusetts Office of Coastal Zone Management (CZM) and the U.S. Geological Survey (USGS) in Woods Hole, MA as part of a cooperative agreement to provide high resolution bathymetry and backscatter intensity maps and digital GIS information for resource management, scientific research, industry and the public.

Data are not intended for navigational use. These data should not be used at resolutions for which it is not intended. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS), as the source of this information.

All of the NOAA survey vessels were equipped with Trimble DSM212L Differential Global Positioning System (DGPS) receivers. Launch 1005, which collected all of the multibeam bathymetry, was also equipped with a TSS POS/MV Model 320 (Position and Orientation System for Marine Vessels). Standard bathymetric processing, including tide corrections, soundings accuracy, and quality control were done by the NOAA Office of Coast Survey.

The original geophysical data for this project were collected during four hydrographic surveys conducted by NOAA NOS in 2000 and 2001 on the NOAA Ship Whiting and its launches 1005/1014. Multibeam bathymetric data were acquired with a Reson SeaBat 8101 and sidescan sonar backscatter data were acquired with Edgetech model 272-T (100 kHz) or the Klein T-5500 (455 kHz) sonar systems.

Process description:

A hull-mounted Reson SeaBat 8101 acquired the shallow-water multibeam data for all four surveys.  The Reson 8101 was operated at a frequency of 240 kHz and a maximum speed of 6 knots.  The system is designed for operation in water depths of 5 to 125 m, and has a horizontal range of 75 to 500 m that depends on water depth.  Each time the system fires or "pings", it collects 101 individual soundings in a swath oriented perpendicular to the vessel track.  Acquisition was monitored in real time with the ISIS software (version 5.29) and recorded to XTF format.  NOAA Office of Coast Survey converted the XTF data to CARIS HDCS (Hydrographic Data Cleaning System) format, then processed and tide-corrected the data with CARIS HIPS (Hydrographic Information Processing System) software. The CARIS HIPS database was transfered to the USGS/CZM in 2004 for use in this project.

The NOAA acquisition vessels were also equipped with Odom Echotrac DF3200 MKII echosounders that logged high-frequency (100 kHz) vertical-beam soundings concurrently throughout the sidescan sonar and multibeam bathymetry surveying operations.  Vertical-beam soundings were recorded in Hypack raw format and later converted to CARIS HDCS format.  The NOAA Office of Coast Survey cleaned and merged the data and performed tide corrections using CARIS HIPS.

Bathymetry soundings from the multibeam surveys were exported from CARIS HIPS at a 2-meter grid interval for each of the four survey areas and vertical-beam soundings from surveys H10990, H10992, and H10994 were exported from CARIS HIPS at a 5-meter grid interval. The vertical-beam data from survey H01991 were processed by NOAA prior to their use of CARIS and a separate xyz file was provided for these soundings. The eight soundings files were merged to create a master file of over 17 million soundings within the survey areas.

GMT (Generic Mapping Tools - http://gmt.soest.hawaii.edu/) was used to create an interpolated grid of the bathymetry for the entire region. The soundings data were formatted for input into GMT and then filtered through the GMT block median routine to reduce the data and speed up the interpolation process. An interpolated grid was created using the GMT surface routine with a grid cell size of 30 m and a tension parameter of 0.5. The GMT grid was converted to an ASCII grid using the Gdal utility gdal_translate (FWTools, version 1.0.0a7 and Gdal, version 1.3.1).

In ArcMap (Spatial Analyst -> Raster Calculator) evaluated the expression "bh_30mbath > -32" the resulting was a temporary file 'calculation' with value = 1 where the multibeam data exists. In ArcMap (Spatial Analyst -> Convert -> Raster to Features) the temp grid 'Calculation' was converted to a polygon shapefile (Input raster: Calculation, Field: Value, Output geometry type: Polygon).

Although this data set has been used by the U.S. Geological Survey (USGS), no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

compositebathybnds: Composite Bathymetry Boundaries from Boston Harbor and Approaches
	Data format: Shapefile File or table name: compositebathybnds Coordinate system: Universal Transverse Mercator Theme keywords: U.S. Geological Survey, USGS, Coastal and Marine Geology Program, CMGP, Woods Hole Science Center, WHSC, Massachusetts Office of Coastal Zone Management, CZM, Seafloor, Marine Geology, ESRI Shapefile, field activity serial number RAFA04019, Multibeam, Bathymetry, Reson SeaBat 8101, Reson, Topography, Odom Echotrac DF3200 MKII echosounder, echosounder, Odem, single-beam, vertical-beam, National Oceanic and Atmospheric Administration, NOAA, National Ocean Service, NOS, NOAA Ship Whiting, Hydrographic Survey, 32-bit floating point, oceans and estuaries, elevation, boundaries
Abstract: This data is the boundary polygon for the high-resolution bathymetric measurements of the seafloor from Boston Harbor and the harbor approaches, Massachusetts. Approximately 170 km² of sidescan sonar and bathymetric data were collected by the National Oceanic and Atmospheric Administration (NOAA) Ship Whiting in 2000 and 2001 and reprocessed and gridded by the Massachusetts Office of Coastal Zone Management (CZM) and the U.S. Geological Survey (USGS).

FGDC and ESRI Metadata: