Additional USGS Geoscience data can be found by geographic location or by publication series.
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:
• 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