2-m Bathymetric Grid of National Oceanic and Atmospheric Administration (NOAA) Survey H11445 in Long Island Sound, North of Plum Island, New York (H11445_2M_GEO, Geographic, WGS84)

Bathymetric data were acquired in extended Triton data format (XTF) and recorded digitally through an ISIS data acquisition system. Reson 8101 and 8125 multibeam echosounders hull-mounted on two 29' launches deployed from the NOAA ship Thomas Jefferson were used to acquire the sounding data. All positioning and attitude were determined with Trimble DSM212L DGPS receivers and Applanix POS/MV Model 320 v.4 inertial navigation systems. The data were processed using CARIS HIPS (Hydrographic Image Processing System) software for quality control, and to incorporate sound velocity and tidal corrections. Sound velocity corrections were derived using frequent SEACAT CTD (conductivity-temperature-depth) profiles. Typically, a CTD cast was conducted every three to four hours of multibeam acquisition. Tidal zone corrections were calculated from data acquired at the New London, Thames River, CT tidal gauge. The vertical resolution of the multibeam data is approximately 0.5% of the water depth. The data were gridded to 2-m resolution and saved as a CARIS HIPS database. Vertical datum is mean lower low water; X and Y units are meters; UTM Zone 18, NAD83.

The fieldsheet from survey H11445 (average depths, not the shoal based fieldsheets) was imported into the Fledermaus v6.7 program DMagic to make an equivalent digital terrain model (DTM) file. The floating point format for each sounding depth point is preserved during data import. Additionally, this fieldsheet was imported into DMagic as "gridded data", therefore re-gridding of data did not occur during the import process and thus preserved the original resolutions of the CARIS fieldsheet: H11445 2 meter cell size. Projection information for the H11445 CARIS fieldsheet is: UTM Zone 18N NAD 83.

The H11445 DTM file was then exported as an ESRI ASCII raster file from the DMagic program (H11445_2m.asc). The export process preserves the floating point values of the grid cell nodes.

The H11445 ESRI ASCII raster file was imported into ArcMap v9.3 using the ASCII to Raster tool (ArcToolbox, Conversion Tools, To Raster). The only option set here is to import each sounding grid cell value as a floating point number. The resulting grid, H11445_2m_utm, retains the original CARIS fieldsheet 2 meter grid.

The UTM ESRI grid was then reprojected using the data management tool Project Raster (ArcToolbox, Data Management Tools, Projections and Transformations) from UTM Zone 18N, NAD 83 to Geographic, WGS84. The options specified in the Project Raster tool were: 1. Input coordinate system: NAD_1983_UTM_Zone_18N 2. Output coordinate system: GCS_WGS_1984 3. Geographic transformation method: NAD_1983_WGS_1984_5 4. Resampling technique: BILINEAR 5. Output cell size: 0.000021 (decimal degrees, default as calculated by ArcMap for a 2 meter cell size) The geographic transformation selected is the most accurate one provided by ESRI as it ties in WGS84 with ITRF96, thus reflecting the earth centered offset (x-y-z) between WGS84 and NAD83 (from the ESRI Knowledge Base Document Number 24159). Used ArcGIS v9.3.

Edits to the metadata were made to fix any errors that MP v 2.9.32 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). The distribution format name was modified in an attempt to be more consistent with other metadata files of the same data format. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent.

Added keywords section with USGS persistent identifier as theme keyword.