Multibeam Backscatter of the Los Angeles, California Margin

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Frequently-anticipated questions:

What does this data set describe?

Title: Multibeam Backscatter of the Los Angeles, California Margin
XYZ ASCII format data generated from the 1996, 1998, and 1999 multibeam sonar surveys of the Los Angeles, California Margin. The data include high-resolution corrected acoustic backscatter. These datasets in their present form were not originally intended for publication. The bathymetry and backscatter have data-collection and processing artifacts. These data are being made public to satisfy a Freedom of Information Act request. Care must be taken not to confuse artifacts with real seafloor morphology and acoustic backscatter.
Information for USGS Coastal and Marine Geology related activities are online at <> <> <>

  1. How should this data set be cited?

    United States Geological Survey, Coastal and Marine Geology (CMG), Chief, 2002, Multibeam Backscatter of the Los Angeles, California Margin.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -118.850
    East_Bounding_Coordinate: -117.754
    North_Bounding_Coordinate: 34.029
    South_Bounding_Coordinate: 33.334

  3. What does it look like?

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

    Beginning_Date: 30-Sep-1996
    Ending_Date: 29-Oct-1996
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: XYZ ASCII

  6. How does the data set represent geographic features?

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

      This is a Point data set. It contains the following vector data types (SDTS terminology):

      • Point

    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 0.00002, 0.00004. Longitudes are given to the nearest 0.00002, 0.00004. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is WGS84.
      The ellipsoid used is WGS84.
      The semi-major axis of the ellipsoid used is 6378137.00 meters.
      The flattening of the ellipsoid used is 1/0.003352811.

  7. How does the data set describe geographic features?


    Sample of Backscatter XYZ ASCII file

     Longitude, Latitude, DN Value
    (decimal degree, decimal degree, DN value)
    Entity_and_Attribute_Detail_Citation: none

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    Peter Dartnell
    United States Geological Survey (USGS)
    Physical Scientist
    USGS, MailStop 999, 345 Middlefield Road
    Menlo Park, CA 94025-3561

    (650) 329-5460 (voice)
    (650) 329-5411 (FAX)

Why was the data set created?

These data are intended for science researchers, students, policy makers, and the general public. The data can be used with geographic information systems (GIS) or other software to display acoustic backscatter data of the Los Angeles, California Margin.

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: 30-Oct-1996 (process 1 of 1)
    The multibeam bathymetry and acoustic backscatter data were collected along a continuous swath perpendicular to the direction of the ship using Kongsberg Simrad EM300, EM1000, and dual EM3000 multibeam sonar systems. The data are cleaned of bad navigation and depth readings and corrected for tides to mean lower low water datum. The depth readings are gridded into a common grid. The gridded data are converted to ArcInfo GRID format using ArcInfo's ASCIIGRID command. The GRID was converted to an XYZ ASCII file by using the GRIDPOINT, ADDXY, and Tables' UNLOAD commands.

    Person who carried out this activity:

    Peter Dartnell
    United States Geological Survey (USGS)
    USGS, MailStop 999, 345 Middlefield Road
    Menlo Park, CA 94025-3561

    (650) 329-5460 (voice)
    (650) 329-5411 (FAX)

  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?

    Not determined.

  2. How accurate are the geographic locations?

    0.5 meters

  3. How accurate are the heights or depths?

    0.05 percent of the water depth. Depths corrected to mean lower low water datum.

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


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

    Point features present.

How can someone get a copy of the data set?

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

Access_Constraints: None

Please recognize the U.S. Geological Survey (USGS) as the source of this information. USGS-authored or produced data and information are in the public domain.

  1. Who distributes the data set? (Distributor 1 of 1)

    United States Geological Survey (USGS)
    345 Middlefield Rd., MS-999
    Menlo Park, CA 94025

    (650)329-5460 (voice)

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

    C-1-96-SC, A-3-98-SC, and C-1-99-SC data sets

  3. What legal disclaimers am I supposed to read?

    These data not intended for navigational purposes.

    Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, these data and information are provided with the understanding that they are not guaranteed to be usable, timely, accurate, or complete. Users are cautioned to consider carefully the provisional nature of these data and information before using them for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences. Conclusions drawn from, or actions undertaken on the basis of, such data and information are the sole responsibility of the user.

    Neither the U.S. Government nor any agency thereof, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any data, software, information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights.

    Trade, firm, or product names and other references to non-USGS products and services are provided for information only and do not constitute endorsement or warranty, express or implied, by the USGS, USDOI, or U.S. Government, as to their suitability, content, usefulness, functioning, completeness, or accuracy.

  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 12-Apr-2004
Metadata author:
Pete Dartnell
United States Geological Survey (USGS)
Physical Scientist
USGS, MailStop 999, 345 Middlefield Road
Menlo Park, CA 94025-3561

(650) 329-5460 (voice)
(650) 329-5411 (FAX)

Metadata standard:
Content Standard for Digital Geospatial Metadata ("CSDGM version 2") (FGDC-STD-001-1998)

Generated by mp version 2.8.11 on Fri May 21 11:37:28 2004