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Sea floor maps showing topography, sun-illuminated topographic imagery, and backscatter intensity of the Stellwagen Bank National Marine Sanctuary Region off Boston, Massachusetts

Frequently anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  3. What similar or related data should the user be aware of?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How should this data set be cited?

   Valentine, Page C. , Middleton, Tammie J. , and Fuller, Sarah J. , 2001, Sea floor maps showing topography, sun-illuminated topographic imagery, and backscatter intensity of the Stellwagen Bank National Marine Sanctuary Region off Boston, Massachusetts: U.S. Geological Survey Open-File Report 00-410, U.S. Geological Survey, Reston, VA.

   Online Links:

   • <http://pubs.usgs.gov/openfile/of00-410/>

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -70.600

   East_Bounding_Coordinate: -70.033

   North_Bounding_Coordinate: 42.800

   South_Bounding_Coordinate: 42.083

3. What does it look like?

   <http://pubs.usgs.gov/openfile/of00-410/images/pseudo2.gif> (GIF)

   Reduced-size copy of the backscatter image with topography (color indicates backscatter, shading indicates topography) 351x599 pixels, 32-bit RGB true color, 120 kbytes.

4. Does the data set describe conditions during a particular time period?

   Beginning_Date: 15-Aug-1994

   Ending_Date: 22-Sep-1998

   Currentness_Reference:

   Multibeam data were collected from the years of 1994 to 1996. Contours and imagery were generated and edited through 1998.

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: map

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?

      This is a Raster data set. It contains the following raster data types:

      • Dimensions 3150 x 1884, type pixel

   2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest .00003. Longitudes are given to the nearest .00003. Latitude and longitude values are specified in Decimal Degrees.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is GRS1980.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.
      

      Vertical_Coordinate_System_Definition:

      Depth_System_Definition:

      Depth_Datum_Name: Local surface

      Depth_Resolution: 1

      Depth_Distance_Units: meters

      Depth_Encoding_Method: Attribute values

7. How does the data set describe geographic features?

   Bathymetric contour line

   polyline within coverage bathymer

   CONTOUR

   Depth of the bathymetric contour. Values are in meters above sea level, so all values given are negative. Double of width 13, but values are integer. Another attribute "INTERVAL" contains the same data stored as an integer.

   Range of values
   Minimum:	-270
   Maximum:	-5
   Units:	meters
   Resolution:	5

   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 350 degrees and a vertical exaggeration of four times. In effect, topographic relief is enhanced by having the sun illuminate the sea floor from a position 10 degrees west of 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. The topographic imagery is identical to that shown on Sheet 3 of this report.
   Backscatter Imagery
   This map combines the sun-illuminated topography with the backscatter intensity (shown here in color) of the sea floor. Backscatter intensity is a measure of the hardness and roughness of the sea floor as determined from the strength of sound waves reflected from the seabed during the survey. High-backscatter materials (red and orange) are coarse sand, gravel (including piles and ridges of boulders), and rock outcrops. Moderate backscatter (green) represents sand or muddy sand. Low backscatter (blue) represents sandy mud and mud. These interpretations apply best in regions 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 track lines are artifacts of data collection. Blank areas represent places where no data exists.

   Entity_and_Attribute_Detail_Citation: <http://pubs.usgs.gov/openfile/of00-410/methods.htm>

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • Page C. Valentine
   • Tammie J. Middleton
   • Sarah J. Fuller

2. Who also contributed to the data set?

   U.S. Geological Survey, National Oceanic and Atmospheric Administration, Canadian Hydrographic Service, University of New Brunswick

3. To whom should users address questions about the data?
   Page C Valentine
   U.S. Geological Survey, ER
   384 Woods Hole Road
   Woods Hole, MA 02543-1598
   USA
   

   508-457-2239 (voice)
   508-457-2310 (FAX)
   pvalentine@usgs.gov
   

Why was the data set created?

Development of a GIS database of sea floor imagery that is accessible to scientists, policymakers, managers, and the general public.

How was the data set created?

1. From what previous works were the data drawn?

   Valentine and others (1999) (source 1 of 3)

   Valentine, P.C., Baker, J.L., Unger, T.S., Evans, J., and Polloni, C., 1999, Sea floor topographic, backscatter, and interpretive maps and bottom photos of the Massachusetts Bay Disposal Site region off Boston, Massachusetts: U.S. Geological Survey Open-File Report 98-344.

   Other_Citation_Details: 1 CD-ROM

   Type_of_Source_Media: paper

   Source_Contribution: Massachusetts Bay Disposal Site Maps and Features on CD-ROM

   Valentine and others (1998) (source 2 of 3)

   Valentine, P.C., Baker, J.L., Unger, T.S., and Polloni, C., 1998, Sea floor topographic map and perspective view imagery of Quadrangles 1-18, Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File-Report 98-138.

   Type_of_Source_Media: paper

   Source_Contribution:

   Sea Floor Topography of Quadrangles 1-18 in Stellwagen Bank National Marine Sanctuary on CD-ROM

   Valentine and others (2000) (source 3 of 3)

   Valentine, P.C., Unger, T.S., Baker, J.L., and Polloni, C., 2000, Sun-illuminated sea floor topographic map and perspective view imagery of Quadrangles 1-18, Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 99-363.

   Type_of_Source_Media: paper

   Source_Contribution:

   Sun-Illuminated Sea Floor Topography of Quadrangles 1-18 in Stellwagen Bank National Marine Sanctuary on CD-ROM

2. How were the data generated, processed, and modified?

   Date: 1998 (process 1 of 1)

   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's Boston Tide Gauge (Station 8443970) and merged into the data set using UNB's tidal routines. The topographic information was converted into an ascii textfile containing lat, long, and depth fields, using a script created by Bill Danforth at the U.S. Geological Survey. The ascii file was brought into Arc/Info, and a grid was generated and processed using ESRIs Arc/Info version 7.0.4 software. A point coverage containing depth values was created using the routine point-generate.
   The grid was created based on the depth values for each of the points using the command pointgrid. The grid was filtered with a 9 by 9 focalmedian filter. Contours were generated using latticecontour. All editing and edgematching was done by hand using arcedit. The shaded relief images shown here were created using a light source that is 45 degrees above the horizon from an azimuth of 350 degrees. The vertical exaggeration in the images is four times. In effect, topographic relief is enhanced by illuminating the sea floor from a position 10 degrees west of 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 include small highs and lows and unnatural-looking features and patterns that are oriented parallel or perpendicular to survey tracklines.

   Person who carried out this activity:
   

   William W Danforth
   U.S. Geological Survey, ER
   Geologist
   384 Woods Hole Road
   Woods Hole, MA 02543-1598
   USA
   

   508-457-2274 (voice)
   508-457-2310 (FAX)
   bdanforth@usgs.gov
   

3. What similar or related data should the user be aware of?

   Valentine, Page C. , Unger, Tanya S. , and Baker, Jessica L. , 1999, Backscatter Intensity and Sun-illuminated Sea Floor Topography of the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geologial Survey Geologic Investigations Series Map I-2676C.

   Other_Citation_Details: scale 1:60,000, 1 sheet

   Valentine, Page C. , Unger, Tanya S. , and Baker, Jessica L. , 1999, Sea Floor Topography of the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geologial Survey Geologic Investigations Series Map I-2676A.

   Other_Citation_Details: scale 1:60,000, 1 sheet

   Valentine, Page C. , Unger, Tanya S. , and Baker, Jessica L. , 1999, Sun-illuminated Sea Floor Topography of the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geologial Survey Geologic Investigations Series Map I-2676B.

   Other_Citation_Details: scale 1:60,000, 1 sheet

How reliable are the data; what problems remain in the data set?

1. How well have the observations been checked?

   The ship's position was determined with an accuracy of 10 m or better using a Magnavox 4200 geographic 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 the sound velocity profile of the water column in the area to be surveyed. This information is used by the data acquisition system to correct for the refraction of the transmitted multibeam sound signal as it travels 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 Boston tide gauge were used to reference depth data to mean lower low water.
   Sounding rates depend on water depth but vary from 2 to 4 per second in water depths less than 100 meters. Horizontal spatial resolution at these sounding rates is on the order of 10% of the water depth at 16 knots; however, vertical resolution is approximtely 1% or better in the same depth range.

2. How accurate are the geographic locations?

   Sounding rates depend on water depth but vary from 2 to 4 per second in water depths less than 100 meters. Horizontal spatial resolution at these sounding rates is on the order of 10% of the water depth at 16 knots; however, vertical resolution is approximtely 1% or better in the same depth range.

3. How accurate are the heights or depths?

   Sounding rates depend on water depth but vary from 2 to 4 per second in water depths less than 100 meters. Horizontal spatial resolution at these sounding rates is on the order of 10% of the water depth at 16 knots; however, vertical resolution is approximtely 1% or better in the same depth range.

4. Where are the gaps in the data? What is missing?

   Both the bathymetric and the sidescan-sonar backscatter data are 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.

5. How consistent are the relationships among the observations, including topology?

   Multibeam echo sounder data was 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 16 knots. The ship has two submerged torpedo-shaped hulls that support the main deck via two thin struts. 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 detects changes in pitch, roll, and heave of the vessel. The motion information is recorded concurrently with the acquired multibeam signal and both are logged in a single file on the Sun workstation and made available to other workstations for further processing.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None

Use_Constraints: None.

1. Who distributes the data set? (Distributor 1 of 2)
   Page C Valentine
   U.S. Geological Survey, ER
   384 Woods Hole Road
   Woods Hole, MA 02543-1598
   USA
   

   508-457-2239 (voice)
   508-457-2310 (FAX)
   pvalentine@usgs.gov
   

2. What's the catalog number I need to order this data set?

   USGS Open-File Report 00-410

3. What legal disclaimers am I supposed to read?

   This publication was prepared by members of the US Geological Survey. Neither USGS or the United States Government nor any agency thereof, nor any of their employees, make 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 necessarily 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.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	Bathymetric contours, quadrangle boundaries, coastline, and boundary of the Stellwagen Bank National Marine Sanctuary. in format ArcInfo export (version 8.0) Size: 6 megabytes
     Network links:	<http://pubs.usgs.gov/openfile/of00-410/arcexprt/bathymer.e00> <http://pubs.usgs.gov/openfile/of00-410/arcexprt/coastmer.e00> <http://pubs.usgs.gov/openfile/of00-410/arcexprt/quadbnd.e00> <http://pubs.usgs.gov/openfile/of00-410/arcexprt/sbnmsbnd.e00>

     Data format:	Backscatter Imagery and Sun-Illuminated Sea Floor Topography in format TIFF (version 6.0) Size: 114 megabytes
     Network links:	<http://pubs.usgs.gov/openfile/of00-410/tif/sunillum.tif> <http://pubs.usgs.gov/openfile/of00-410/tif/pseudo.tif>

   • Cost to order the data: none

---

1. Who distributes the data set? (Distributor 2 of 2)
   USGS Information Services
   Box 25286 Denver Federal Center
   Denver, CO 80225
   USA
   

   1-888-ASK-USGS (voice)
   303-202-4693 (FAX)
   ask@usgs.gov
   

2. What's the catalog number I need to order this data set?

   USGS Open-File Report 00-410

3. What legal disclaimers am I supposed to read?

   This publication was prepared by members of the US Geological Survey. Neither USGS or the United States Government nor any agency thereof, nor any of their employees, make 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 necessarily 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.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	Backscatter Imagery and Sun-Illuminated Sea Floor Topography in format TIFF (version 6.0) Size: 114 megabytes
     Media you can order:	CD-ROM (format ISO 9660)

   • Cost to order the data: See <http://mapping.usgs.gov/esic/prices/index.html>

Who wrote the metadata?

Dates:

Last modified: 10-Jan-2002

Metadata author:

Page C Valentine
U.S. Geological Survey, ER
384 Woods Hole Road
Woods Hole, MA 02543-1598
USA

508-457-2239 (voice)
508-457-2310 (FAX)
pvalentine@usgs.gov

Metadata standard:

Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)