Sea floor topography and backscatter intensity of the historic area remediation site

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Frequently anticipated questions:


What does this data set describe?

Title:
Sea floor topography and backscatter intensity of the historic area remediation site
Abstract:
This data set includes topography and backscatter intensity of the sea floor of the Historic Area Remediation Site (HARS), located offshore of New York and New Jersey. The data were collected with a multibeam sea floor mapping system on surveys conducted November 23 - December 3, 1996, October 26 - November 11, 1998, and April 6 - 30, 2000. The surveys were conducted using a Simrad EM 1000 multibeam echo sounder mounted aboard the Canadian Hydrographic Service vessel Frederick G. Creed. This multibeam system utilizes 60 electronically aimed receive beams spaced at intervals of 2.5 degrees that insonify a strip of sea floor up to 7.5 times the water depth (swath width of 100 to 200 m within the survey area). The horizontal resolution of the beam on the sea floor is approximately 10% of the water depth (3-5 meters in the survey region). Vertical resolution is approximately 1 percent of the water depth, or 0.3 m. Maps derived from the mulitbeam observations show sea floor topography, shaded relief, and backscatter intensity (a measure of sea floor texture and roughness) at a spatial resolution of 3 m/pixel. These data have been reprocessed from those presented in Butman and others (2002) (see cross reference) to correct for an error in the software that projected the data on a sphere rather than on the WGS84 ellipsoid, and to stretch the backscatter intensity and shaded relief images to match the Hudson Shelf Valley images. The horizontal error in placement of the data published by Butman and others (2002) was 0 in the northwestern corner of the HARS, and reached about 12 m in the southeastern corner. Further work is needed to match the backscatter intensity for the 1996, 1998, and 2000 surveys.
  1. How might this data set be cited?
    U.S. Geological Survey, 2003, Sea floor topography and backscatter intensity of the historic area remediation site: U.S. Geological Survey Open-File Report 01-470, U.S. Geological Survey, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Butman, Bradford, Gutierrez, Benjamin T., ten Brink, Marilyn Buchholtz, Schwab, William C., Blackwood, Dann S., Mecray, Ellen L., and Middleton, Tammie J., 2003, Photographs of the sea floor offshore of New York and New Jersey: U.S. Geological Survey Open-File Report 01-470, U.S. Geological Survey, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -73.900124
    East_Bounding_Coordinate: -73.812264
    North_Bounding_Coordinate: 40.433605
    South_Bounding_Coordinate: 40.349975
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 1996
    Ending_Date: 2000
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: remote-sensing image and raster digital data
  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 2487 x 3098, type Pixel
    2. What coordinate system is used to represent geographic features?
      The map projection used is Mercator.
      Projection parameters:
      Standard_Parallel: 40.0
      Longitude_of_Central_Meridian: -75
      False_Easting: 0
      False_Northing: 0
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 3
      Ordinates (y-coordinates) are specified to the nearest 3
      Planar coordinates are specified in meters
      The ellipsoid used is World Geodetic System 84.
      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: Mean lower low water
      Depth_Resolution: 0.3
      Depth_Distance_Units: Meters
      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
    The multibeam observations in the HARS were originally published in Butman and others (2002), U.S. Geological Survey Open-File Report 00-503 (see cross-reference citation). These data have been reprocessed to correct for an error in the software that projected the data on a sphere rather than on the WGS84 ellipsoid, and to stretch the backscatter intensity and shaded relief images the same as the Hudson Shelf Valley images.
  3. To whom should users address questions about the data?
    U. S. Geological Survey
    Attn: Bradford Butman
    Oceanographer
    384 Woods Hole Rd
    Woods Hole, MA
    USA

    508-548-8700 x2212 (voice)
    508-457-2309 (FAX)
    bbutman@usgs.gov

Why was the data set created?

These data are included in this publication to provide bathymetry and backscatter intensity of the sea floor for maps showing the locations of images and samples obtained in the New York Bight.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 1996 (process 1 of 2)
    (1) Data and acquisition processing at sea. After the echo sounder data were logged onto the hard disk of the Sun workstation, a suite of processing software developed by the Ocean Mapping Group (www.omg.unb.ca/~jhc/SwathEd.html) was used to correct for artifacts and errors that may have been introduced during data collection. This software also enhanced the corrected data by resolving beam pattern and aspect ratio distortions and by imposing a linear contrast stretch before it generated bathymetric and sidescan sonar image mosaicks in a Mercator projection. All data processing described here is initiated using Silicon Graphics workstations as soon as each acquisition file is closed by the Simrad Mermaid workstation (usually at the end of each survey line). Additional processing was done in the lab to correct for fluctuations in sea level during the survey and for artifacts in the data files that were not corrected in the field (see below). The processing and editing steps on board the ship were:
    (A.) Demultiplex, or unravel, the acquired Simrad data files using RT to generate separate files containing navigation, depth soundings, sidescan sonar backscatter values, and sound velocity information.
    (B.) Automatically reject bad data (autoRejectSoundings). For the multibeam soundings, reject data outside expected depth ranges (operator's decision based on nautical chart data); for navigation data, reject fixes with poor GPS statistics.
    (C.) Edit the navigation data on-screen using jview to remove undesirable points, including turns at the ends of survey lines.
    (D.) Edit the multibeam soundings on-screen using swathed to remove individual anomalous soundings.
    (E). Merge tidal information and the corrected navigation back (mergetide and mergenav) into the data files. Tidal information was obtained from the NOAA tide server using tide station 8531680 located at Sandy Hook, Final tidal corrections were made in the lab using a different procedure (see below).
    (F.) Map the bathymetric soundings from each processed data file onto a Mercator grid using weigh_grid with node spacings and scale selected by the operator.
    (G.) Map the extracted sidescan sonar backscatter values onto a digital mosaic using mos2 in the Mercator projection at a scale selected by the user.
    (H.) Using addSUN, generate bathymetric raster files using the mapped grid node information to depict the depth information in a shaded relief Mercator map. A Mercator projection allows individual map areas to be joined edge to edge when creating a composite image. The shaded relief images were generated using a sun elevation angle of 45 degrees from an azimuth of 0 degrees, and a vertical exaggeration of four times to emphasize sea floor features.
    (I.) Generate a false colored image using mix_ci by combining the bathymetric and backscatter raster mosaics into a single image, also in the Mercator projection.
    (2) Data processing and analysis in the lab included:
    (A.) Removing sound refraction artifacts from the data (using the refraction tool in swathed) due to insufficient sound velocity profile information and varying water masses within the study area.
    (B.) The measured elevations were adjusted for fluctuations in sea level during the survey by subtracting tidal elevations predicted by a tidal model and low-frequency sea level observed at the National Oceanic and Atmospheric Administration Sandy Hook tide station located at 40 degrees 28 minutes N., 74 degrees 0.6 minutes W. The tidal model utilized 9 constituents derived from a 4-month bottom pressure record obtained at Station A, located at 40 degrees 23.4 minutes N., 73 degrees 47.1 minutes W. in 38 m water depth about 2.7 km east of the HARS, during the winter of 1999-2000. An estimate of the error due to sea level remaining in the multibeam observations after the sea level correction is about 3 cm.
    (C.) Two corrections have been made to the HARS multibeam data as published in Butman and others (2002). (1) The backscatter intensity data between 180-220 was stretched to 0-255 (The data published in 2002 between 180-225 was stretched to 0-255). The shaded relief data between 150-200 was stretched to 0-255 (as in the 2002 data). Aging of the multibeam transducer and software changes implemented to correct the near-nadir response make the backscatter intensity observed in 1996, 1998, and 2000 not directly comparable. Further work is needed to match the backscatter intensities between the 1996, 1998 and 2000 surveys. (2) The data were also reprocessed to correct for an error in the UNB software that projected the data on a sphere rather than on the WGS84 ellipsoid. The horizontal error in placement of the data published by Butman and others (2002) was 0 in the northwestern corner of the HARS, and reached about 12 m in the southeastern corner.
    All mapped files are in the Mercator projection, having a central longitude of -75 degrees West, a latitude of true scale of 40 degrees north and the horizontal datum is WGS84. The vertical datum is mean lower low water. Person who carried out this activity:
    William Danforth
    U.S. Geological Survey
    Operational Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    508-548-8700 x2274 (voice)
    508-457-2310 (FAX)
    bdanforth@usgs.gov
    Hours_of_Service: 8 a.m. to 5 p.m. EST
    Date: 16-Dec-2002 (process 2 of 2)
    Creation of original metadata record Person who carried out this activity:
    Brad Butman
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA

    508-457-2212 (voice)
  3. What similar or related data should the user be aware of?
    Butman, Bradford, Danforth, William W., Knowles, Stephen C., May, Brian, and Serrett, Laurie, 2002, Sea floor topography and backscatter intensity of the Historic Area Remediation Site (HARS), offshore of New York, based on multibeam surveys conducted in 1996, 1998, and 2000.: U.S. Geological Survey Open-File Report 00-503, U.S. Geological Survey, Woods Hole, MA.

    Online Links:


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?
    These data were navigated with a Differential Global Positioning System (DGPS); they are accurate to +/- 3 meters, horizontally.
  3. How accurate are the heights or depths?
    These data have been corrected for vessel motion (roll, pitch, heave, yaw) and tidal offsets, and referenced to mean lower low water. The theoretical vertical resolution of the Simrad EM-1000 multibeam echosounder is 1 % of water depth; roughly 30 - 50 cm within the study area. However, the working vertical resolution of the system, is roughly +/- 50 cm.
  4. Where are the gaps in the data? What is missing?
    No further processing or modifications will be made to these data.
  5. How consistent are the relationships among the observations, including topology?

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: This information is not for navigational purposes.
  1. Who distributes the data set? (Distributor 1 of 1)
    Bradford Butman
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Road
    Woods Hole, Massachusetts
    USA

    508-548-8700 x2212 (voice)
    508-457-2309 (FAX)
    bbutman@usgs.gov
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    These data were prepared by an agency of the United States Government. Neither 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. Although all data have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 04-Feb-2015
Last Reviewed: 22-Jul-2004
Metadata author:
Peter N Schweitzer
USGS Midwest Area
Collection manager, USGS Geoscience Data Clearinghouse, http://geo-nsdi.er.usgs.gov/
Mail Stop 954
12201 Sunrise Valley Dr
Reston, VA
USA

703-648-6533 (voice)
703-648-6252 (FAX)
pschweitzer@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

This page is <https://geo-nsdi.er.usgs.gov/metadata/open-file/01-470/harsmb.faq.html>
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