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Maps Showing Sea Floor Topography, Sun-Illuminated
Sea Floor Topography, and Backscatter Intensity of
Quadrangles 1 and 2 in the Great South Channel Region,
Western Georges Bank

Page C. Valentine, editor

U.S. GEOLOGICAL SURVEY GEOLOGIC INVESTIGATIONS SERIES MAP I–2698

2002, Version 1.0

Prepared in cooperation with the National Oceanic and Atmospheric Administration


Metadata also available as - [Parseable Text]

Metadata:

   •  Identification Information
   •  Data Quality Information
   •  Spatial Data Organization Information
   •  Spatial Reference Information
   •  Entity and Attribute Information
   •  Distribution Information
   •  Metadata Reference Information


Identification_Information:

        Citation:
                Citation_Information:
                        Originator: Page C. Valentine, editor
                        Publication_Date: 2002
                        Title: Maps Showing Sea Floor Topography, Sun-Illuminated Sea Floor Topography,
                                  and Backscatter Intensity of Quadrangles 1 and 2 in the Great South Channel
                                  Region, Western Georges Bank
                        Geospatial_Data_Presentation_Form: map
                        Series_Information:
                                Series_Name: U.S. Geological Survey Geologic Investigations Series Map
                                Issue_Identification: I-2698
                        Publication_Information:
                                Publication_Place: Reston, VA
                                Publisher: U.S. Geological Survey
        Description:
                Abstract:
                        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, sand transported by the
                        strong north-south-flowing tidal and storm currents has
                        formed large, east-west-trending dunes. These bedforms
                        (ranging between 5 and 20 m in height) contrast strongly
                        with, and partly mask, the subdued topography of the older
                        glacial features.
                Purpose:
                        A multibeam echo sounder survey of the Great South
                        Channel region was conducted in November 1998. The
                        area surveyed is approximately 172 sq nmi (590 sq km) 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
                        and the sedimentary environments and benthic habitats of
                        the region. The imagery will serve as the basis for
                        conducting studies on (1) 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.
        Time_Period_of_Content:
                Time_Period_Information:
                        Range_of_Dates/Times:
                                Beginning_Date: 1998
                                Ending_Date: 1998
                Currentness_Reference: Multibeam data were collected in 1998. Contours and imagery
                                                       were generated and edited through 2000.
        Status:
                Progress: Complete
                Maintenance_and_Update_Frequency: As needed
        Spatial_Domain:
                Bounding_Coordinates:
                        West_Bounding_Coordinate: -69.050000000
                        East_Bounding_Coordinate: -68.78666667
                        North_Bounding_Coordinate: 41.13333333
                        South_Bounding_Coordinate: 40.900000000
        Keywords:
                Theme:
                        Theme_Keyword_Thesaurus: None
                        Theme_Keyword: Geographic Information Systems
                        Theme_Keyword: GIS
                        Theme_Keyword: Woods Hole Field Center
                        Theme_Keyword: WHFC
                        Theme_Keyword: United States Geological Survey
                        Theme_Keyword: USGS
                        Theme_Keyword: SIMRAD SUBSEA EM 1000
                        Theme_Keyword: Frederick G. Creed
                        Theme_Keyword: Swath Bathymetry
                        Theme_Keyword: Multibeam Echo Sounder
                        Theme_Keyword: Topographic data
                        Theme_Keyword: Sea floor topography
                        Theme_Keyword: Bathymetry
                        Theme_Keyword: Sun-illuminated imagery
                        Theme_Keyword: Shaded relief imagery
                        Theme_Keyword: Sea floor backscatter
                        Theme_Keyword: Sedimentary environment
                        Theme_Keyword: Sea floor habitat
                Place:
                        Place_Keyword_Thesaurus: None
                        Place_Keyword: Great South Channel
                        Place_Keyword: GSC
                        Place_Keyword: Georges Bank
                        Place_Keyword: Gulf of Maine
                        Place_Keyword: Atlantic Ocean
                        Place_Keyword: Ocean
                        Place_Keyword: Shallow EEZ
                        Place_Keyword: EEZ
        Access_Constraints: None
        Use_Constraints: None
        Point_of_Contact:
                Contact_Information:
                        Contact_Person_Primary:
                                Contact_Person: Page C. Valentine
                                Contact_Organization: U.S. Geological Survey, ER
                        Contact_Position: Geologist
                        Contact_Address:
                                Address_Type: mailing and physical address
                                Address: 384 Woods Hole Road
                                City: Woods Hole
                                State_or_Province: MA
                                Postal_Code: 02543-1598
                                Country: USA
                        Contact_Voice_Telephone: 508-457-2239
                        Contact_Facsimile_Telephone: 508-457-2310
                        Contact_Electronic_Mail_Address: pvalentine@usgs.gov
        Data_Set_Credit:
                U.S. Geological Survey, National Oceanic and
                Atmospheric Administration, Canadian Hydrographic
                Service, University of New Brunswick
        Native_Data_Set_Environment: OSF1 UNIX, ARC/INFO version 7.0.3
        Cross_Reference:
                Citation_Information:
                        Originator: Page C. Valentine
                        Originator: Tammie J. Middleton
                        Originator: Jeremy T. Malczyk
                        Publication_Date: 2002
                        Title: Sea Floor Topography of Quadrangle 1, map A of Maps Showing Sea Floor
                                  Topography, Sun-Illuminated Sea Floor Topography, and Backscatter Intensity
                                  of Quadrangles 1 and 2 in the Great South Channel Region, Western Georges
                                  Bank
                        Edition: 1
                        Geospatial_Data_Presentation_Form: map
                        Series_Information:
                                Series_Name: U.S. Geological Survey Geologic Investigations Series Map
                                Issue_Identification: I-2698A
                        Publication_Information:
                                Publication_Place: Reston, VA
                                Publisher: U.S. Geological Survey
                        Other_Citation_Details: scale 1:25,000, 1 sheet
        Cross_Reference:
                Citation_Information:
                        Originator: Page C. Valentine
                        Originator: Tammie J. Middleton
                        Originator: Jeremy T. Malczyk
                        Publication_Date: 2002
                        Title: Sun-Illuminated Sea Floor Topography of Quadrangle 1, map B of Maps
                                 Showing Sea Floor Topography, Sun-Illuminated Sea Floor Topography, and                                  Backscatter Intensity of Quadrangles 1 and 2 in the Great South Channel Region,                                  Western Georges Bank
                        Edition: 1
                        Geospatial_Data_Presentation_Form: map
                        Series_Information:
                                Series_Name: U.S. Geological Survey Geologic Investigations Series Map
                                Issue_Identification: I-2698B
                        Publication_Information:
                                Publication_Place: Reston, VA
                                Publisher: U.S. Geological Survey
                        Other_Citation_Details: scale 1:25,000, 1 sheet                                
        Cross_Reference:
                Citation_Information:
                        Originator: Page C. Valentine
                        Originator: Jeremy T. Malczyk
                        Originator: Tammie J. Middleton
                        Publication_Date: 2002
                        Title: Sea Floor Topography of Quadrangle 2, map C of Maps Showing Sea Floor
                                  Topography, Sun-Illuminated Sea Floor Topography, and Backscatter Intensity
                                  of Quadrangles 1 and 2 in the Great South Channel Region, Western Georges
                                  Bank
                        Edition: 1
                        Geospatial_Data_Presentation_Form: map
                        Series_Information:
                                Series_Name: U.S. Geological Survey Geologic Investigations Series Map
                                Issue_Identification: I-2698C
                        Publication_Information:
                                Publication_Place: Reston, VA
                                Publisher: U.S. Geological Survey
                        Other_Citation_Details: scale 1:25,000, 1 sheet
        Cross_Reference:
                Citation_Information:
                        Originator: Page C. Valentine
                        Originator: Jeremy T. Malczyk
                        Originator: Tammie J. Middleton
                        Publication_Date: 2002
                        Title: Sun-Illuminated Sea Floor Topography of Quadrangle 2, map D of Maps
                                 Showing Sea Floor Topography, Sun-Illuminated Sea Floor Topography, and                                  Backscatter Intensity of Quadrangles 1 and 2 in the Great South Channel Region,                                  Western Georges Bank
                        Edition: 1
                        Geospatial_Data_Presentation_Form: map
                        Series_Information:
                                Series_Name: U.S. Geological Survey Geologic Investigations Series Map
                                Issue_Identification: I-2698D
                        Publication_Information:
                                Publication_Place: Reston, VA
                                Publisher: U.S. Geological Survey
                        Other_Citation_Details: scale 1:25,000, 1 sheet  
        Cross_Reference:
                Citation_Information:
                        Originator: Page C. Valentine
                        Originator: Tammie J. Middleton
                        Originator: Sarah J. Fuller
                        Publication_Date: 2002
                        Title: Backscatter Intensity and Sun-Illuminated Sea Floor Topography of Quadrangles
                                 1 and 2, map E of Maps Showing Sea Floor Topography, Sun-Illuminated Sea
                                 Floor Topography, and Backscatter Intensity of Quadrangles 1 and 2 in the Great                                  South Channel Region, Western Georges Bank
                        Edition: 1
                        Geospatial_Data_Presentation_Form: map
                        Series_Information:
                                Series_Name: U.S. Geological Survey Geologic Investigations Series Map
                                Issue_Identification: I-2698E
                        Publication_Information:
                                Publication_Place: Reston, VA
                                Publisher: U.S. Geological Survey
                        Other_Citation_Details: scale 1:25,000, 1 sheet      

Data_Quality_Information:

        Attribute_Accuracy:
                Attribute_Accuracy_Report:
                        The survey was conducted using a multibeam echo
                        sounder installed aboard the Canadian Hydrographic
                        Service vessel Frederick G. Creed, a SWATH (Small
                        Waterplane Area Twin Hull) ship that surveys at speeds up
                        to 15 knots. The ship's position was determined with an
                        accuracy of 10 m or better using a Magnavox 4200 global
                        positioning system (GPS) receiver in conjunction with
                        differential GPS corrections transmitted by U.S. Coast
                        Guard radio beacons. At the start of each day, casts were
                        made to record them sound velocity profile of the water
                        column in the area to be surveyed. This information was
                        used by the data acquisition system to correct for the
                        refraction of the transmitted multibeam sound signal as it
                        traveled through the water to and from the sea floor. Sound
                        velocity information was updated during the day whenever
                        the survey moved from one area to another. Tidal
                        corrections based on NOAA's Nantucket tide gauge
                        (station 8449130) were used to reference depth data to
                        mean lower low water. The multibeam echo sounder data
                        were collected by means of a Simrad Subsea EM 1000
                        Multibeam Echo Sounder (95 kHz) that is permanently
                        installed in the hull of the Creed. In water depths between
                        5 and 200 m, the EM 1000 generates 60 aimed beams
                        spaced at intervals of 2.5 degrees, that insonify a swath of
                        sea floor measuring in width approximately 7.5 times the
                        water depth. Sounding rates depend on water depth but
                        vary from 2 to 4 per second in water depths less than 100
                        m. Horizontal spatial resolution at these sounding rates is
                        on the order of 10 percent of the water depth at 15 knots;
                        however, vertical resolution is approximately 1 percent or
                        better in the same depth range.
        Logical_Consistency_Report:
                Multibeam echo sounder data were collected aboard the
                Canadian Hydrographic Service vessel Frederick G. Creed,
                an aluminum SWATH (Small Waterplane Area Twin Hull)
                ship that surveys at speeds up to 15 knots. The ship has
                two submerged torpedo-shaped hulls that support the main
                deck via two thin struts from each hull. This design
                reduces wave motion on the ship and resistance to the
                ship's forward motion through the water, thus making it a
                very stable platform at high survey speeds. Stability of the
                ship is also enhanced by the computer-controlled action of
                four stabilizer fins located fore and aft on the inboard side of
                the hulls. The stabilizers control the pitch and roll of the
                vessel and allow adjustment of the heel and trim of the ship
                while under way. An Applied Analytics POS/MV motion
                sensor, located in the hull near the EM 1000 transducer,
                detected changes in pitch, roll, and heave of the vessel.
                The motion information was recorded concurrently with the
                acquired multibeam signal and both were logged in a single
                file on the Sun workstation and made available to other
                workstations for further processing.
        Completeness_Report:
                Both the bathymetric and the sidescan-sonar backscatter
                data were displayed in real time on the Sun workstation
                using software designed and written by the Ocean Mapping
                Group, University of New Brunswick. This display allows
                data gaps to be identified during the survey and also gives
                a measure of the data quality.
        Positional_Accuracy:
                Horizontal_Positional_Accuracy:
                        Horizontal_Positional_Accuracy_Report:
                                Sounding rates depend on water depth but vary from 2 to 4
                                per second in water depths less than 100 m.
                                Horizontal spatial resolution at these sounding rates is on
                                the order of 10 percent of the water depth at 15 knots;
                                however, vertical resolution is approximately 1 percent or
                                better in the same depth range.
                Vertical_Positional_Accuracy:
                        Vertical_Positional_Accuracy_Report:
                                Sounding rates depend on water depth but vary from 2 to 4
                                per second in water depths less than 100 m.
                                Horizontal spatial resolution at these sounding rates is on
                                the order of 10 percent of the water depth at 15 knots;
                                however, vertical resolution is approximately 1 percent or
                                better in the same depth range.
        Lineage:
                Process_Step:
                        Process_Description:
                                Multibeam data were processed using SwathEd, a suite of
                                multibeam software editing and display tools developed by
                                Dr. John Hughes Clarke of the Ocean Mapping Group,
                                University of New Brunswick (UNB). The navigation and
                                topographic data were both edited using this software.
                                Tidal corrections were obtained from NOAA Nantucket tide
                                gauge (station 8449130) and merged into the data set using
                                UNB's tidal routines. The topographic information was
                                converted into an ASCII text file containing latitude,
                                longitude, and depth fields, using a script created by William
                                W. Danforth of the U.S. Geological Survey. The ASCII file
                                was brought into Arc/Info geographic information system
                                software (Environmental Systems Research Institute, Inc.,
                                version 7.0.3), and a 9-meter grid was generated and
                                processed. A point coverage containing depth values was
                                created using the "point-generate" routine. The grid was
                                created based on the depth values for each of the points
                                using the command "pointgrid". The grid was filtered with a
                                3-cell by 3-cell focal median filter. Five-meter contours were
                                generated using the "latticecontour" routine. All editing and
                                edge-matching were done by hand using ArcEdit. The
                                shaded relief images shown here were created using a light
                                source positioned 45 degrees above the horizon from an
                                azimuth of 0 degrees. The vertical exaggeration in the
                                images is four times. In effect, topographic relief is
                                enhanced by illuminating the sea floor from the north so that
                                shadows are cast on the southern flanks of seabed
                                features. Some features in the images are artifacts of data
                                collection. They are especially noticeable where the
                                seabed is smooth, and they include small highs and lows
                                and unnatural-looking features and patterns that are
                                oriented parallel or perpendicular to survey tracklines, which
                                run north-south. Large east-west-trending bedforms
                                (typically 5 to 10 m in height, but ranging up to 20 m)
                                characterize parts of the sea floor in this region. The
                                multibeam echo sounder had difficulty imaging these
                                features because they are oriented at right angles to the
                                ship's tracks and display steep sides and narrow crests. As
                                a result, the crests of some of these bedforms display small
                                gaps or lows that do not exist.
                        Process_Date: 1998
                        Process_Contact:
                                Contact_Information:
                                        Contact_Person_Primary:
                                                Contact_Person: William W. Danforth
                                                Contact_Organization: U.S. Geological Survey, ER
                                        Contact_Position: Geologist
                                        Contact_Address:
                                                Address_Type: mailing and physical address
                                                Address: 384 Woods Hole Road
                                                City: Woods Hole
                                                State_or_Province: MA
                                                Postal_Code: 02543-1598
                                                Country: USA
                                        Contact_Voice_Telephone: 508-457-2274
                                        Contact_Facsimile_Telephone: 508-457-2310
                                        Contact_Electronic_Mail_Address: bdanforth@usgs.gov

Spatial_Data_Organization_Information:

        Direct_Spatial_Reference_Method: Raster
        Raster_Object_Information:
                Raster_Object_Type: Pixel
                Row_Count: 3170
                Column_Count: 3707

Spatial_Reference_Information:

       Horizontal_Coordinate_System_Definition:
                Geographic:  
       Vertical_Coordinate_System_Definition:
                Altitude_System_Definition:
                        Altitude_Datum_Name: local surface
                        Altitude_Resolution: 1
                        Altitude_Distance_Units: Meters
                        Altitude_Encoding_Method: Attribute values

Entity_and_Attribute_Information:

        Detailed_Description:
                Entity_Type:
                        Entity_Type_Label: Bathymetric contour line
                        Entity_Type_Definition: polyline within coverage q1contrs
                        Entity_Type_Definition_Source: coverage q1contrs
                Attribute:
                        Attribute_Label: CONTOUR
                        Attribute_Definition:
                                Depth of the bathymetric contour. Values are in meters
                                above sea level, so all values are given a negative.
                                Double of width 13. Another attribute "INTERVAL"
                               
contains the same data stored as an integer.
                        Attribute_Definition_Source: bathymetry
                        Attribute_Domain_Values:
                                Range_Domain:
                                        Range_Domain_Minimum: -100
                                        Range_Domain_Maximum: -45
                        Attribute_Units_of_Measure: meters
                        Attribute_Measurement_Resolution: 5
        Overview_Description:
                Entity_and_Attribute_Overview:
                        Sun-illuminated topographic imagery:
                        This map combines contoured topography and
                        sun-illuminated topographic imagery. The image shown
                        here uses a sun elevation angle of 45 degrees above the
                        horizon from an azimuth of 0 degrees and a vertical
                        exaggeration of four times. In effect, topographic relief is
                        enhanced by having the sun illuminate the sea floor from
                        the north so that shadows are cast on the southern flanks
                        of seabed features. Unnatural-looking stripes and patterns
                        oriented parallel or perpendicular to survey track lines are
                        artifacts of data collection. Blank areas represent places
                        where no data exists.
                        Backscatter imagery:
                        This map combines the sun-illuminated topography with the
                        backscatter intensity (shown in color) of the sea floor.
                        Backscatter intensity is a measure of the hardness and
                        roughness of the sea floor as determined by the strength
                        of the sound waves reflected from the seabed during the
                        survey. High-backscatter values (red, orange, and yellow)
                        represent coarse sand and gravel, including piles and
                        ridges of boulders. Moderate- and low-backscatter values
                        (yellow, green, and blue) represent sand. These
                        interpretations apply best in areas of low regional
                        topography, because steep slopes can divert the paths of
                        some of the reflected sound waves away from the survey
                        vessel. Thus seabed that slopes steeply away from the
                        survey track can produce a lower backscatter intensity
                        than if it were level. Unnatural-looking stripes and patterns
                        oriented parallel or perpendicular to survey tracklines are
                        artifacts of data collection. Blank areas represent places
                        where no data exists.
                Entity_and_Attribute_Detail_Citation:


Distribution_Information:

        Distributor:
                Contact_Information:
                        Contact_Person_Primary:
                                Contact_Person: Page C. Valentine
                                Contact_Organization: U.S. Geological Survey, ER
                        Contact_Position: Geologist
                        Contact_Address:
                                Address_Type: mailing and physical address
                                Address: 384 Woods Hole Road
                                City: Woods Hole
                                State_or_Province: MA
                                Postal_Code: 02543-1598
                                Country: USA
                        Contact_Voice_Telephone: 508-457-2239
                        Contact_Facsimile_Telephone: 508-457-2310
                        Contact_Electronic_Mail_Address: pvalentine@usgs.gov
        Resource_Description: U.S. Geological Survey I-2698
        Distribution_Liability:
                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.
        Standard_Order_Process:
                Digital_Form:
                        Digital_Transfer_Information:
                                Format_Name: TIFF
                                Format_Information_Content:
                                        Backscatter Imagery and Sun-Illuminated Sea Floor
                                        Topography
                                File_Decompression_Technique: No compression applied
                                Transfer_Size: 114 megabytes
                        Digital_Transfer_Option:
                                OffLine_Option:
                                        Offline_Media: CD-ROM
                                        Recording_Format: ISO 9660
                Fees: See <http://mapping.usgs.gov/esic/prices/>

Metadata_Reference_Information:

        Metadata_Date: 2002
        Metadata_Contact:
                Contact_Information:
                        Contact_Person_Primary:
                                Contact_Person: Page C. Valentine
                                Contact_Organization: U.S. Geological Survey, ER
                        Contact_Position: Geologist
                        Contact_Address:
                                Address_Type: mailing and physical address
                                Address: 384 Woods Hole Road
                                City: Woods Hole
                                State_or_Province: MA
                                Postal_Code: 02543-1598
                                Country: USA
                        Contact_Voice_Telephone: 508-457-2239
                        Contact_Facsimile_Telephone: 508-457-2310
                        Contact_Electronic_Mail_Address: pvalentine@usgs.gov
        Metadata_Standard_Name: Content Standard for Digital Geospatial Metadata
        Metadata_Standard_Version: FGDC-STD-001-1998
        Metadata_Access_Constraints: None
        Metadata_Use_Constraints: None


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