10-m resolution gray-scale image of multibeam backscatter intensity in Massachusetts Bay (MB_BACKGS10M.TIF)

A suite of processing software (called SwathEd) (www.omg.unb.ca/~jhc/SwathEd.html), developed by the Ocean Mapping Group at the University of New Brunswick, Canada, was used to process and grid the multibeam bathymetric soundings and produce shaded-relief images. The metadata for the grids describes the processing steps applied to the navigation and bathymetric soundings. The following processing steps produced the grayscale image of backscatter intensity: 1. Anomalous soundings which were not edited in the field were removed using SwathEd (see metadata for bathymetric grids for description). 2. Create a blank 8 bit map file: Command line: make_blank mosaic_file This command commences a dialog to enable an 8 bit image and input the map boundaries and resolution. Then the "blank" file is copied to two files required by the mosaic program: Command line: cp mosaic_file.blank mosaic_file.mos Command line: cp mosaic_file.blank mosaic_file.ran 3. Create backscatter files that can be then mosaicked from the backscatter time series: Command line: getBeamPattern filename (prefix only) Command line: makess -pixel 3.0 -beam_patt beampatt filename (prefix only) output.ss Command line: glfill output.ss output.ss_fill (fills in data dropouts). 4. Mosaic all the backscatter files created in the last step (for each output.ss_fill). Command line: mos2 -autoseam -maxazi 10 -maxdist 10 mosaic_file output.ss_fill 5. Use a two point linear contrast stretch to enhance the shaded relief image: Command line: stretchacres -low 180 -high 220 -in mosaic_file -out mosaic_file.stretch 6. Create a tiff from the backscatter mosaic file using the netpbm utilities (http://netpbm.sourceforge.net/): Command line: rawtopgm -headerskip 1024 image_width image_height mosaic_file.stretch | pnmtotiff -none - > mosaic_pseudo.tif 7. Create an ESRI world file (tfw) for the mosaic tiff image for import to ArcView or ArcGIS. Copy bounding box and resolution from the jview program output to the .tfw file. Command line: jview mosaic_file.stretch

Reprocessing to correct projection error An error in the UNB processing software that resulted in the multibeam observations not being properly projected onto a plane was discovered in 2003. These software errors were corrected and the data re-gridded. The images of backscatter intensity in the Stellwagen Bank region presented here may differ from preliminary versions included in the following publications: Butman, B., and Lindsay, J.A. (Eds.), 1999, A marine GIS Library for Massachusetts Bay: focusing on Disposal sites, Contaminated Sediments, and Sea Floor Mapping: U.S. Geological Survey Open-File Report 99-439, 1 CD-ROM. (Also available on line at http://pubs.usgs.gov/of/of99-439/start.htm) Gutierrez, B.T., Butman, Bradford, and Blackwood, D.S., 2001, Photographs of the sea floor of western Massachusetts Bay, offshore of Boston, Massachusetts, July 1999: U.S. Geological Survey Open-File Report 00-427, 1 CD-ROM. (Also available on line at http://pubs.usgs.gov/of/of00-427/) Valentine, P.C., Middleton, T., and Fuller, S., 2001, Maps showing sea floor topography, sun-illuminated sea floor topography, and backscatter intensity of the Stellwagen Bank National Marine Sanctuary region off Boston, Massachusetts: USGS Open-File Report #00-410, 1 CD-ROM, scale 1:60,000. (Also available on line at http://pubs.usgs.gov/of/of00-410/)

Image shifted 1/2 grid cell to northwest (using the ArcMap/Data Management Tools/Projections and Transformations/Raster/Shift tool) to correct for an error identified in the SwathEd gridding algorithm in 2007. World files corrected.

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. Other minor edits were probably performed (title, publisher, publication place, etc.). The source information was incomplete and had to be modified to meet the standard. 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.