USING THIS CD-ROM / SYSTEM REQUIREMENTS

This CD-ROM (Compact Disc-Read Only Memory) has been produced in accordance with the ISO 9660 CD-ROM Standard and is therefore capable of being read on any computing platform that has appropriate CD-ROM driver software installed.

Includes Encapsulated PostScript, PostScript, Portable Document File, Registered TIF, and Arc Export formats of 5 individual maps.

This CD-ROM was designed to be used on computers equipped with a CD-ROM reader and mouse, both IBM compatibles and Macintosh hardware. It does not contain a built-in display software, but can be read with any HTML-compatible browser like NETSCAPE, MOSAIC, and INTERNET EXPLORER by opening the "index.htm" file included in the CD-ROM. Some organization links found on this CD-ROM are to the World Wide Web and will work only if connected to the Web. There are PDF files included on this CD-ROM for viewing and printing. You must have the most recent version of Adobe Acrobat Reader downloaded in order to view them; this is free software.

DISCLAIMER

This Compact Disc-Read Only Memory (CD-ROM) publication was prepared by the U.S. Geological Survey. Neither the USGS nor the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

INTRODUCTION

A multibeam echo sounder survey of the Great South Channel region was conducted in November 1998. The area surveyed is approximately 172 square nautical miles (590 square kilometers) and is presented here as two quadrangles at a scale of 1:25,000 (1 centimeter on the map represents 250 meters on the sea floor). The purpose of the survey was to collect detailed topographic and seabed backscatter imagery that will serve as the basis for mapping the sea floor morphology, the sedimentary environments, and the benthic habitats of the region. The imagery will also serve as the basis for conducting studies (1) on the geological and biological processes that form and alter the seabed, (2) the distribution of benthic habitats, and (3) the function of habitats in the life cycles of groundfish and other benthic species. The Georges Bank Mapping Project is a cooperative effort of the U.S. Geological Survey and the National Oceanic and Atmospheric Administration (NOAA), with support from the University of New Brunswick and the Canadian Hydrographic Service.

The Great South Channel separates the western part of Georges Bank from Nantucket Shoals and is a major conduit for the exchange of water between the Gulf of Maine to the north and the Atlantic Ocean to the south. Water depths range mostly between 65 and 80 m in the region. A minimum depth of 45 m occurs in the east-central part of the mapped area, and a maximum depth of 100 m occurs in the northwest corner. The channel region is characterized by strong tidal and storm currents that flow dominantly north and south. Major topographic features of the seabed were formed by glacial and postglacial processes. Ice containing rock debris moved from north to south, sculpting the region into a broad shallow depression and depositing sediment to form the irregular depressions and low gravelly mounds and ridges that are visible in parts of the mapped area. Many other smaller glacial features probably have been eroded by waves and currents at work since the time when the region, formerly exposed by lowered sea level or occupied by ice, was invaded by the sea. The low, irregular and somewhat lumpy fabric formed by the glacial deposits is obscured in places by drifting sand and by the linear, sharp fabric formed by modern sand features. Today, the strong north-south-flowing tidal and storm currents transport sand to construct large, east-west-trending sand dunes. These large bedforms contrast strongly with, and partly mask, the subdued topography of the older glacial features.

CONTENTS

The 5 maps and their components are included in this CD-ROM in 5 different formats:

        1. Encapsulated PostScript (EPS)

        2. PostScript (PS)

        3. Portable Document File (PDF)

        4. Registered TIF (TIF)

        5. Arc Export (e00)

There are 6 directories in this CD-ROM:

Directory ARC Export:

This directory has the Arc Export (e00)  files.   The Arc Export files are coverages in a geographic projection with Geodetic Reference System 1980 and North American Datum 1983.  The attributes which accompany these coverages are depth and depression.  The depth field contains positive values for each contour line.  The depression field contains values representing topographic lows or depressions (identified by 1) and regular topographic contours (identified by 0).

Directory HTML:

This directory has the HTML files used for documentation on this CD-ROM.

Directory IMAGES:

This directory has the logo graphic files for some of the HTML files.

Directory PDF:

The Portable Document Files are included for viewing and printing using Adobe Acrobat Reader.

Directory POSTSCRP:

The Encapsulated PostScript (EPS) and PostScript files (PS) were generated from Adobe Illustrator version 9.0 and contain maps in a Mercator projection with the longitude of the central meridian at 68°55' W., and the latitude of true scale at 40°50' N.  The EPS files are included for printing.

The PostScript files are included for printing and require a maximum page size of 40 by 60 in. (101.6 x 152.4 cm).

Directory TIF:

The TIF and associated TIF World File (TFW) can be incorporated into a GIS database for use with ArcView. The TIF World Files project the TIFs in a geographic projection with Geodetic Reference System 1980 and North American Datum 1983.