ArcInfo Grid of the 30 meter pixel Composite Bathymetry of Boston Harbor and Approaches (BH_30MBATH, UTM 19, WGS84)

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 ArcGIS 9.0 (ArcToolbox) the ASCII grid was imported to an ESRI raster grid (cell size = 30 m).

Edits to the metadata were made to fix any errors that MP v 2.9.30 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. Process dates were not in the original metadata file, so a value of unknown was used. In the case of the vertical resolution, the value of 9999 was entered to indicate that the original metadata did not contain the required information. The source citation of the source contribution was blank, so that information was populated based on the information contained in the process steps. Other minor edits were probably performed (title, publisher, publication place, etc.). 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.