Metadata: 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 Larger_Work_Citation: Citation_Information: Series_Information: Publication_Information: 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: Single_Date/Time: Range_of_Dates/Times: Beginning_Date: 1998 Ending_Date: 1998 Multiple_Dates/Times: 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 Stratum: Temporal: 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_Organization_Primary: 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 Security_Information: 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: Source_Information: Source_Citation: Citation_Information: Series_Information: Publication_Information: Larger_Work_Citation: Citation_Information: Series_Information: Publication_Information: Source_Time_Period_of_Content: Time_Period_Information: Single_Date/Time: Range_of_Dates/Times: Multiple_Dates/Times: 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_Organization_Primary: 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 Depth_System_Definition: 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 Attribute_Value_Accuracy_Information: 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: Available_Time_Period: Time_Period_Information: Single_Date/Time: Range_of_Dates/Times: Multiple_Dates/Times: 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_Organization_Primary: 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 Metadata_Security_Information: