Sea floor topography is a fundamental underpinning for research and management in the coastal ocean. Four bathymetric data sets are included on this CD-ROM; (1) A compilation of all available data from the Gulf of Maine gridded at 15 arc seconds (approximately 0. 5 km) and 30 arc seconds, including land topography and selected contours (from Signell and others, 1999); (2) 5 m and 20 m contours based on a map of the Massachusetts Bay Region published by Valentine, Schmuck and others (1995); (3) Bathymetry and shaded relief images from multibeam echosounder surveys of the Stellwagen Bank National Marine Sanctuary (Valentine, Baker, Unger, and Polloni, 1998; Valentine, Baker, Unger, and Polloni, 1999), the Massachusetts Bay Disposal Site (Valentine, Baker, Unger, Evans, and Polloni, 1998), and western Massachusetts Bay (Butman and others, in prep.); and (4) Bathymetry from surveys of the Industrial Waste Site in 1988 (2 m contours) and 1993 (SAIC).

Signell and others (1999) collected data from available sources on the World Wide Web and from CD-ROM products. The data included digital sounding data, digitized contour line data and previously gridded products from a variety of sources. Generic Mapping Tools (GMT) was used to produce 15 and 30 second grids that were exported as XYZ ASCII files and read into ARC/INFO to produce grid files.

These data are available in ARC/INFO grid format (for use in ArcView with Spatial Analyst) as well as TIFF format. Both sets of tifs and grids are provided in Geographic coordinate system (Gom15grd, Gom30grd, Gom15tfg.tif, Gom30tfg.tif) and Mercator projection (Gom15grm, Gom30grm, Gom15tfm.tif, Gom30tfm.tif). In order to discern the detail in the bathymetric grids, it is necessary to load the legend "gom_grd.avl" for each of the 4 grids.

The Mercator parameters are as follows: datum = NAD83, spheroid = GRS80, central meridian = -70.31667, latitude of true scale = 41.65.

Contour lines were created in ARC/INFO from gom15grd. A finer contour interval was used in shallower depths. (Contoured at -4000, -3000, -2000, -1000, -500, -400, -300, -280, -260, -240, -220, -200, -180, -160, -140, -120, -100, -90, -80, -70, -60, -50, -40, -30, -20, -15, -10, -5 meters).

A multibeam echosounder survey of the Stellwagen Bank National Marine Sanctuary and western Massachusetts Bay was conducted by the U.S. Geological Survey (USGS) in cooperation with the National Oceanic and Atmospheric Administration, the University of New Brunswick, and the Canadian Hydrographic Service (Valentine and Butman, 1998; Valentine, Baker, Unger, and Polloni, 1998). The images and data from these surveys provide a detailed description of the bathymetry and surficial geology. They are utilized in ongoing USGS studies of the long-term fate of sediments and contaminants, biological habitats, and contribute to the USGS effort to map the continental margin of the U.S. Exclusive Economic Zone (Gardner and others, 1998).

For publication purposes, the region has been divided into 21 Quadrangles (see USGS quad coverage). For each quadrangle, paper maps at a scale of 1:25,000 showing bathymetry and shaded relief will be published.  The bathymetry for quadrangles 1-18 are published in paper form (Valentine, Baker and others, 1997a-i; Valentine, Unger and others, 1997a-i) and in digital form (Valentine, Baker, Unger, and Polloni, 1998).  The shaded relief maps are published in paper (Valentine, Unger, and Baker, 1999) and in digital form (Valentine, Unger, Baker, and Polloni, 1999). Interpretive maps of Quadrangles 1-18, showing the sea floor environments, are in preparation. Publication of the multibeam data for Quadrangles 19-21 is in preparation (Butman and others, in prep.).

Maps of the Massachusetts Bay Disposal Site, also based on multibeam surveys, have been published at a scale of 1:10,000, and 1:12,500 (Valentine, Danforth and others, 1996). The data is published digitally (Valentine, Baker, Unger, Evans, and Polloni, 1998). These data have been converted to ARC/INFO grids and are included on this CD-ROM.

The multibeam sea floor mapping systems data are provided at two horizontal resolutions on this CD-ROM. The maps of western Massachusetts Bay (USGS Quadrangles 19-21) were gridded at 6 m pixel size.  The contours in the Stellwagen Bank National Marine Sanctuary (Quadrangles 1-18) were produced from bathymetry gridded at 10 m resolution.

Four types of maps, each providing a different view of the sea floor, can be generated from the multibeam echosounder data.

The grids should be displayed in the project files with the intended colors. However, if the user adds these themes to new views, the following instructions will be helpful.

Colormap files (.clr) allow the grids to be displayed with the correct color scheme when the grid theme is added as "image data". This happens automatically as long as the .clr is in the same directory as the grid and they have the same name. Since colormap files do not have a "nodata" designation, the cells with no values are automatically colored black. The user may change this by pressing the "colormap..." button in the Image Legend Editor, scrolling to the bottom of the list to find "NODATA", and changing it to white or transparent.

If the Spatial Analyst extension is loaded, a third data source type called "grid data" is available in the "add theme" dialog box. If the grids are added as grid data, ArcView will automatically choose its own colors. The user can load the correct legend (.avl) from the legend editor. The backscatter and shaded relief grids use the same legend. To color the pseudocolor shaded relief maps correctly, 2 grids must be opened in the view; the pseudocolor grid and the shaded relief grid for the same area (i.e.: wmbpsdcm and wmbshd_m). Load the appropiate legend to the shaded relief, and then load the legend to the pseudocolor grid. While still in the legend editor press the "advanced" button, choose the shaded relief as the brightness theme (wmbshd_m), and press OK and Apply.

Bothner and others (1992) carried out detailed sidescan sonar mapping of the region surrounding the MWRA ocean outfall, providing a geological framework for selecting sites for long-term monitoring.

Coverages provided in Library 3:   (Summary metadata for files in the Library 3 view are listed alphabetically in the table below. For complete metadata, go to directory "9_biblio" on this CD-ROM and open the file metadata.mdb using Microsoft Access or the file Gismeta.htm using your browser.)