4-m Grid of the Combined Multibeam Bathymetry Generated from National Oceanic and Atmospheric Administration (NOAA) Surveys H12009, H12010, H12011, H12015, H12033, H12137, and H12139 Offshore in Block Island Sound (BISOUND_4MUTM, UTM Zone 19, NAD83)

The 63-m NOAA Ship Thomas Jefferson and two 8.5-m aluminum Jensen launches (3101 and 3102) deployed from the ship acquired multibeam echosounder (MBES) data for 7 hydrographic surveys in Block Island Sound over an approximately 633.6-square kilometer area between May and October 2009. Registry numbers for the completed surveys include: H12009, H12010, H12011, H12015, H12033, H12137, and H12139. The MBES data were collected with a hull-mounted RESON SeaBat 455-kHz 8125 shallow-water system aboard launch 3101 and RESON single frequency (400-kHz) 7125 systems aboard launch 3102 and the NOAA Ship Thomas Jefferson. Original vertical resolution of the MBES data was 0.5 m for water depths less than 20 m and 1 m for the deeper parts of the survey area. The bathymetric datasets were acquired and digitally logged with HYPACK Hysweep, and processed by NOAA using CARIS Hydrographic Image Processing System (HIPS) software for quality control, to incorporate sound velocity and tidal corrections, and to produce the combined bathymetry adjusted for statistical error (BASE) surfaces. Horizontal positioning was by differential global positioning systems (DGPS); HYPACK 2009 was used for acquisition line navigation. Sound-velocity corrections were derived with frequent conductivity-temperature-depth profiles. A Brooke Ocean Technology Moving Vessel Profiler (MVP) with an Applied Microsystems Smart Sound Velocity and Pressure (SV&P) sensor was used to collect sound speed profile data from the ship. Manually deployed Seabird Electronics SBE-19+ CTD units were used to collect sound speed profile data from the launches. Tidal zone corrections were calculated from data acquired by the National Water Level Observation Network stations at New London, Connecticut (8461490); Newport, Rhode Island (8452660); and Montauk, New York (8510560). The vertical datum is mean lower low water; X and Y units are meters, UTM Zone 19, NAD83. Detailed descriptions of the MBES acquisition and processing by NOAA can be found in the Descriptive Reports and in the Data Acquisition and Processing Report.

The field sheets from the surveys (average depths, not the shoal based field sheets) were read back into CARIS HIPS/SIPS software version 7.0. Using the Base Surface -> Combine command within HIPS, all of the source CARIS base surfaces were combined into a master BASE surface (bisound) having a 4 meter grid resolution.

The combined base surface was exported from CARIS as a Bathymetric Attributed Grid (BAG) file. See http://www.opennavsurf.org/papers/ons_fsd.pdf for a description of the BAG format.

The BAG surface was imported into Fledermaus v7.2 to make equivalent digital terrain model (DTM) files. The floating point format for each sounding depth point is preserved during data import. Additionally, the BAG surface was imported into Fledermaus as "gridded data", therefore re-gridding of data did not occur during the import process and thus preserved the original resolution of the CARIS base surface. The DTM was then directly exported to ArcGIS as a bathy raster file using the FMGIS module built into Fledermaus v7.2, retaining all of the projection information (NAD_1983_UTM_Zone_19N) and grid cell size (4 meter node spacing).

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Added keywords section with USGS persistent identifier as theme keyword.