4-m Image of the Northern Half of the Backscatter Intensity Mosaic of the Sea Floor off Northeastern Cape Cod from USGS Cruise 98015 (CAPENORTHMOS_GEO4M_WGS84.TIF, Geographic, WGS84)

Initial Data and acquisition processing at sea: After the echo sounder data were logged onto the hard disk of the Sun workstation, a suite of processing software developed by the Ocean Mapping Group (www.omg.unb.ca/~jhc/SwathEd.html) was used to correct for artifacts and errors that may have been introduced during data collection. This software also enhanced the corrected data by resolving beam pattern and aspect ratio distortions and by imposing a linear contrast stretch before it generated bathymetric and sidescan sonar image mosaics in a Mercator projection. All data processing described here is initiated using Silicon Graphics workstations as soon as each acquisition file is closed by the Simrad Mermaid workstation (usually at the end of each survey line). Additional processing was done in the lab to correct for fluctuations in sea level during the survey and for artifacts in the data files that were not corrected in the field (see below). The processing and editing steps on board the ship were: (A.) Demultiplex, or unravel, the acquired Simrad data files using RT to generate separate files containing navigation, depth soundings, sidescan sonar backscatter values, and sound velocity information. (B.) Automatically reject bad data (autoRejectSoundings). For the multibeam soundings, reject data outside expected depth ranges (operator's decision based on nautical chart data); for navigation data, reject fixes with poor GPS statistics. (C.) Edit the navigation data on-screen using jview to remove undesirable points, including turns at the ends of survey lines. (D.) Edit the multibeam soundings on-screen using swathed to remove individual anomalous soundings. (E). Merge tidal information and the corrected navigation back (mergetide and mergenav) into the data files. Tidal information was obtained from predicted tides using the Xtide program http://www.flaterco.com/xtide/xtide.html), which generated predicted tides based on the harmonic coefficients for Chatham provided by the Xtide program. (F.) Map the bathymetric soundings from each processed data file onto a Mercator grid using weigh_grid with node spacings and scale selected by the operator. The data files capenorth.asc and capenorth.xyz were produced from the gridded data. The data file capenorth.txt is a comma-delimited version of capenorth.xyz. (G.) Map the extracted sidescan sonar backscatter values onto a digital mosaic using mos2 in the Mercator projection at a scale selected by the user.

Map the extracted sidescan sonar backscatter values onto a digital mosaic using the SwathEd utility mos2 in the Mercator projection, having a central longitude of -70.3166667 degrees West, a latitude of true scale of 41.65 degrees north and the horizontal datum is WGS84.

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. Most issues were with blank elements that could actually be removed. This file had a source contribution, but no source citation information. This information was populated based on information in the source contribution. Also, both geographic and planar coordinate systems, a common problem when using ArcCatalog. 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.