Swath bathymetry 13-m-cell-size grid of quadrangle 2 on Stellwagen Bank offshore of Boston, Massachusetts collected by the U.S. Geological Survey aboard the CCGS Frederick G. Creed from 1994-1996

Initial data collection and processing is described in Valentine and others 1999, Valentine 2005, and Butman and others, 2007. A summary of that information is presented here. Surveying was conducted aboard the Canadian Hydrographic Service vessel Frederick G. Creed using a hull mounted multibeam echo sounder. These data were collected using a Simrad Subsea EM1000 operating at 95 kHz. SwathEd software (version unknown) developed by the Ocean Mapping Group, University of New Brunswick, was used to process the bathymetric and navigation data. The processing included editing the data to remove spurious points as well as incorporate tidal corrections. Processing took place over a span of time, 1994 to 1996.

The remaining process steps are a function of incorporating information from the previous publications (noted in cross-references), along with processing notes maintained during data processing. The final SwathEd-produced file (based on a 10-meter-grid-cell size) was converted to an ASCII file using the University of New Brunswick script r4toASCII. The format of the ASCII file is latitude, longitude, and depth. The ASCII file was converted to an ArcInfo ungenerate format using a Perl script. The resulting format is ID, longitude, latitude, and negative depth. Each point has a unique ID value. Using ArcInfo 7.03, the ungenerate format was converted to a coverage format using the 'convert to arc' from 'generate tool' available in ArcTools. The 'build' command with the point option was then used to convert the data to a point coverage. This procedure generates the point locations stored in the ungenerate file, but does not incorporate the depth values. In order to include depth, the ungenerate file - which has location as well as depth - was converted to an ArcInfo table, using 'Tables' in ArcInfo. The structure of the ArcInfo table was defined to include the ID, longitude, latitude, and depth in the appropriate format and size. Longitude and latitude were defined as floating point numbers with six decimal places, while depth was defined as a floating point number with two decimal places. To add the depth value to the point coverage, ArcInfo 'Tables' was used to join the point attribute table (pat) of the coverage to the newly-generated data table based on the ID value. In order to join the tables, the data table ID field had to be renamed to match the automatically assigned coverage ID field. The projection of the point coverage was defined in ArcInfo with the PROJECTDEFINE command and the following parameters: Projection Geographic; Datum NAD83; Units DD; Spheroid GRS80. This process was performed by Jessica Baker in 1997. Then the coverage was projected to the custom Mercator projection using the ArcInfo PROJECT command with the following options: Projection Mercator; Datum NAD83, Spheroid GRS1980; Units Meters; Longitude of Central Meridian -70degrees 19minutes; Latitude of true scale 41degrees 39minutes; False Easting 0; False northing 0. This process was performed by Jessica Baker in 1997. The final step was to convert the points to a grid. This was accomplished using the ArcInfo 'pointgrid' command. The depth attribute was gridded at a cell size of 13 meters, and the background value was set to nodata. This final processing step was performed in 1997, and then again by Tammie Middleton in 2001 and is the grid presented here. The 13-meter cell-size was chosen because it appeared to be the best cell size to avoid striping in the data when processing with the SwathEd software.

The original work on Stellwagen Bank was based on 18 individual quadrangles, and the 13-m cell size grid was the foundation of much of the subsequent work that appears on maps of the Stellwagen Bank area. The information used to generate metadata was based on previous publications, the extensive data processing log prepared by Tanya Unger and Jessica Baker, as well as the individual log files generated during ArcInfo data processing. The information from the various sources was compiled to write the metadata describing this dataset.

The grid was added to ArcMap 10.8.1 and converted to a 32-bit GeoTIFF by right-mouse clicking the dataset then selecting 'Data-Export'. Using the dataset for the extent, spatial reference and cell size parameters, and saving in TIFF format.