Digital Sidescan-Sonar Mosaic collected within the Gulf of Farallones

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Frequently-anticipated questions:

What does this data set describe?

Title:
Digital Sidescan-Sonar Mosaic collected within the Gulf of Farallones
Abstract:
In 1989, the U.S. Geological Survey (USGS) began a major geologic and oceanographic investigation of the Gulf of the Farallones continental shelf system, designed to evaluate and monitor human impacts on the marine environment (Karl and others, 2002). The study region is located off the central California coast, adjacent to San Francisco Bay and encompasses the Gulf of the Farallones National Marine Sanctuary. Geologic mapping of this area included the use of various remote sensing and sampling techniques such as sub-bottom profiling, sidescan-sonar and bathymetric mapping, gravity core and grab sampling, and photography. These data were used to define the surficial sediment distribution, underlying structure and sea floor morphology of the study area. The primary focus of this report is to present a georeferenced, digital sidescan-sonar mosaic of the study region. The sidescan-sonar data were acquired with the AMS-120 (120kHz) sidescan-sonar system during USGS cruise F9-89-NC. The dataset covers approximately 1000 km² of the continental shelf between Point Reyes, California and Half Moon Bay, California, extending west to the continental shelf break near the Farallon Islands. The sidescan-sonar mosaic displays a heterogenous sea-floor environment, containing outcropping rock, ripples, dunes, lineations and depressions, as well as flat, featureless sea floor (Karl and others, 2002). These data, along with sub-bottom interpretation and ground truth data define the geologic framework of the region. The sidescan-sonar mosaic can be used with supplemental remote sensing and sampling data as a base for future research, helping to define the local current regime and predominant sediment transport directions and forcing conditions within the Gulf of Farallones.
  1. How should this data set be cited?

    Sweeney, Edward M. , 2004, Digital Sidescan-Sonar Mosaic collected within the Gulf of Farallones: U.S. Geological Survey, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Sweeney, Edward M. , Danforth, William W. , Karl, Herman A. , O'Brien, Thomas F. , and Schwab, William C. , 2004, The Gulf of Farallones: Sidescan-Sonar Imagery: Open-File Report 2004-1082, U.S. Geological Survey, U.S. Geological Survey, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -123.398630
    East_Bounding_Coordinate: -122.674261
    North_Bounding_Coordinate: 37.998062
    South_Bounding_Coordinate: 37.550340

  3. What does it look like?

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

    Beginning_Date: 02-Aug-1989
    Ending_Date: 15-Aug-1989
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: Raster

  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 12400 x 15900 x 1, type Pixel

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

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 10
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -123.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 4.000000
      Ordinates (y-coordinates) are specified to the nearest 4.000000
      Planar coordinates are specified in meters

      The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.

  7. How does the data set describe geographic features?

    Tiff Image
    Sidescan-sonar image in TIFF format (Source: ESRI)

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?

    Edward M. Sweeney
    U.S. Geological Survey
    Research Assistant
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    (508) 548-8700 x2307 (voice)
    (508) 457-2310 (FAX)
    esweeney@usgs.gov

Why was the data set created?

These data were acquired during the sidescan-sonar survey completed in the Gulf of the Farallones in August, 1989 by the U.S. Geological Survey and were used to define the geological framework of the region.

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: 2004 (process 1 of 1)
    The sidescan-sonar data were acquired using an AMS-120 (120 kHz) sidescan-sonar system. The analog signal from the sidescan-sonar tow vehicle was aquired with and stored on a Triton Technologies, Inc. QMIPS data acquisition system, and then transferred to a Masscomp computer and stored on 8mm 54 MB digital data cartridge tapes. Radiometric corrections and geometric distortions were made using USGS software packages Xsonar and Showimage described in Danforth and others (1991) and Danforth (1997). The sidescan-sonar data were further processed and digitally mosaicked using PCI Geomatica Software and procedures described in Paskevich (1992) resulting in an enhanced, geospatially correct, sidescan-sonar mosaic with 4 meter/pixel resolution. The generated mosaic was exported as a TIFF image, with an associated ESRI world file. Adjustment in contrast levels were then made on the TIFF image file using Adobe Photoshp 6.0.

    Person who carried out this activity:

    Edward M. Sweeney
    U.S. Geological Survey
    Research Assistant
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    (508) 548-8700 x2307 (voice)
    (508) 457-2310 (FAX)
    esweeney@usgs.gov

  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?

    These data were acquired with an AMS-120 (120 kHz) sidescan-sonar system. All data were acquired during one geophysical cruise condcuted in 1989. These data were navigated using GPS and LORAN-C. The horizontal accuracy of these data is roughly +/- 50 meter. Additionally, no layback was estimated for the tow-vehicle. Thus, navigation was based on ship position and not tow-vehicle posistion. Thus, decreasing the horizontal positioning resolution of these data.

  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?

    These data are complete.

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

    These data were acquired with an AMS-120 (120 kHz) sidescan-sonar system, and processed following an identical procedure.

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:
Public domain data from the U.S. government is freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of this dataset.

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

    Nancy Soderberg
    U.S. Geological Survey
    Data Librarian
    384 Woods Hole Rd.
    Woods Hole, MA 02543
    USA

    (508) 548-8700 x2275 (voice)
    (580)457-2313 (FAX)
    nsoderberg@usgs.gov

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

    Sidescan-sonar Mosaic of Gulf of Farallones

  3. What legal disclaimers am I supposed to read?

    Although this data set and its lineage have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data or its 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 items. Users must assume responsibility for the proper use of these data. The data should not be used at resolutions for which they are not intended. The data have not been reviewed for conformity with U.S. Geological Survey editorial standards, or the North American Strigraphic code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government.

  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 07-Apr-2004
Metadata author:
Edward M. Sweeney
U.S. Geological Survey
Research Assistant
384 Woods Hole Rd.
Woods Hole, MA 02543
USA

(508) 548-8700 x2307 (voice)
(508) 457-2310 (FAX)
esweeney@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.8.7 on Mon Jul 19 12:00:12 2004