150-meter bathymetry grid acquired in February and March of 2003 aboard the Ronald H. Brown on U.S. Geological Survey Cruise 2003-008-FA from the Puerto Rico Trench region (RB2003, Esri binary and ASCII grid, UTM zone 19, WGS84)

Bathymetric data were collected using a SeaBeam 2112 (12 kHz) mulitbeam echo sounding system. The system, originally used for high accuracy (SeaBeam Classic) charting of the U.S. Exclusive Economic Zone (EEZ), is capable of hydrographic charting and seafloor acoustic backscatter imaging in water depths of 50 to 11,000 meters with up to 151 beams (2 degree transmit and receive). Swath coverage varies as a function of depth, from 150 degrees at 1,000 meters, to 120 degrees at 5,000 meters, and 90 degrees at 11,000 meters, with a resolution of two degrees. The swath of coverage on the ocean floor is approximately 75% of the water depth. The system operates at an acoustic frequency of 12 KHz and uses transducer arrays that are flush-mounted on the hull in a T-shaped configuration centered on the ship's keel. The horizontal positions for soundings were acquired with several Differential Global Positioning System (DGPS) receivers and one P-Code receiver: a Trimble Centurian P-code GPS, a Magnavox MX-200 GPS, and a Northstar 941x differential GPS. Horizontal sounding positions were recorded to raw multibeam echo sounder data files via SeaBeam's Sea Survey data acquisition software. A conservative estimate of the positional accuracy of the GPS and P-Code receivers is +/- 3 meters.The data pipeline included transferring the SeaBeam MB41 raw data files from the SGI computer to a processing laptop via file transfer protocol (FTP). The raw files were converted using CARIS 5.3 Hips Sips software. The processing crew maintained the same processing procedures as employed by NOAA hydrographic field units. Once the data were converted, a Digital Terrain Model was generated for visual detection of artifacts and missed depths. The next step entailed reviewing and editing the data with CARIS Swath Edit, followed with CARIS Sub Set mode editing. Both editing processes allowed the hydrographer to eliminate data points that were considered artifacts or out of context with the immediate benthic area. After editing, the weighted mean grid was re-generated with a grid resolution of 150 meters. No tide corrections were applied.

The CARIS base surface was opened with Fledermaus Ver 6 and exported as an ESRI ASCII raster grid file with a cell size of 150 meters

The ESRI ASCII raster grid file was imported using the ASCII to RASTER tool in ArcMap 9.2 and exported as an ESRI binary grid.

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.