BackscatterA [8101]--Offshore Pacifica, California

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Frequently anticipated questions:


What does this data set describe?

Title: BackscatterA [8101]--Offshore Pacifica, California
Abstract:

This part of DS 781 presents data for the acoustic-backscatter map of Offshore of Pacifica map area, California. Backscatter data are provided as two separate grids depending on mapping system. The raster data files are included in "BackscatterA_8101_OffshorePacifica.zip," which is accessible from <https://pubs.usgs.gov/ds/781/OffshorePacifica/data_catalog_OffshorePacifica.html>.
The acoustic-backscatter map of the Offshore of Pacifica, California was generated from backscatter data collected by Fugro Pelagos and by California State University, Monterey Bay (CSUMB). Mapping was completed between 2005 and 2007, using a combination of 400-kHz Reson 7125 and 244-kHz Reson 8101 multibeam echosounders. Within the final imagery, brighter tones indicate higher backscatter intensity, and darker tones indicate lower backscatter intensity. The intensity represents a complex interaction between the acoustic pulse and the seafloor, as well as characteristics within the shallow subsurface, providing a general indication of seafloor texture and composition. Backscatter intensity depends on the acoustic source level; the frequency used to image the seafloor; the grazing angle; the composition and character of the seafloor, including grain size, water content, bulk density, and seafloor roughness; and some biological cover. Harder and rougher bottom types such as rocky outcrops or coarse sediment typically return stronger intensities (high backscatter, lighter tones), whereas softer bottom types such as fine sediment return weaker intensities (low backscatter, darker tones).
  1. How should this data set be cited?

    Bretz, Carrie K., Kvitek, Rikk G., Dartnell, Peter, Erdey, Mercedes D., and Phillips, Eleyne L., 2014, BackscatterA [8101]--Offshore Pacifica, California:.

    This is part of the following larger work.

    Edwards, Brian D., Phillips, Eleyne L., Dartnell, Peter, Greene, H. Gary, Bretz, Carrie K., Kvitek, Rikk G., Hartwell, Stephen R., Johnson, Samuel Y., Cochrane, Guy R., Dieter, Brian E., Sliter, Ray W., Ross, Stephanie L., Golden, Nadine E., Watt, Janet T., Chin, John L., Erdey, Mercedes D., Krigsman, Lisa M., Mansion, Michael W., and Endris, Charles A., 2014, California State Waters Map Series--Offshore of Pacifica map area, California: Open-File Report OFR 2014-1260, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -122.65
    East_Bounding_Coordinate: -122.40
    North_Bounding_Coordinate: 37.70
    South_Bounding_Coordinate: 37.54

  3. What does it look like?

    <https://pubs.usgs.gov/ds/781/OffshorePacifica/images/BackscatterA_8101_OffshorePacifica.jpg> (JPEG)
    Acoustic backscatter imagery of offshore Pacifica.

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

    Beginning_Date: 2005
    Ending_Date: 2007
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: GeoTiff

  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, type Grid Cell

    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: 0.9996

      Longitude_of_Central_Meridian: -123.00000

      Latitude_of_Projection_Origin: 0.00000

      False_Easting: 500000.0

      False_Northing: 0.00

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 2.0
      Ordinates (y-coordinates) are specified to the nearest 2.0
      Planar coordinates are specified in Meters

      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 1/298.257223563.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:

    The merged Reson 7125 acoustic-backscatter grid was originally archived as an ESRI grid
    with the following attributes:
    Cell size = 2.0
    Number of rows = 8963
    Number of columns = 8960
    
    Data type = floating point
    
    Boundary
    Xmin = 531130
    Xmax = 549056
    Ymin = 4154950
    Ymax = 4172870
    
    Statistics
    Minimum value = 0
    Maximum value = 254
    Mean = 145.82
    Standard deviation = 27.53
    
    Coordinate system description
    Projection  UTM
    Zone  10
    Datum  WGS84
    Units  meter
    
    The merged Reson 8101 acoustic-backscatter grid was originally archived as an ESRI grid
    with the following attributes:
    Cell size = 2.0
    Number of rows = 8963
    Number of columns = 8960
    
    Data type = floating point
    
    Boundary
    Xmin = 531130
    Xmax = 549056
    Ymin = 4154950
    Ymax = 4172870
    
    Statistics
    Minimum value = 1
    Maximum value = 254
    Mean = 141.60
    Standard deviation = 23.46
    
    Coordinate system description
    Projection  UTM
    Zone  10
    Datum  WGS84
    Units  meter
    
    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
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Physical Scientist
    400 Natural Bridges Dr.
    Santa Cruz, CA 95060-5792
    USA

    (831) 460-7415 (voice)
    (831) 427-4709 (FAX)
    pdartnell@usgs.gov


Why was the data set created?

These data are intended for science researchers, students, policy makers, and the general public. These data can be used with geographic information systems or other software.


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: 2007 (process 1 of 3)
    During the mapping missions, an Applanix position and motion compensation system (POS/MV) was used to accurately position the vessel during data collection, and it also accounted for vessel motion such as heave, pitch, and roll (position accuracy, +/-2 m; pitch, roll, and heading accuracy, +/-0.02 degrees; heave accuracy, +/-5 percent, or 5 cm). KGPS altitude data (Fugro Pelagos, StarFix HP & XP units; CSUMB, NavCom 2050) were used to account for tide cycle fluctuations and sound velocity profiles were collected with an Applied Microsystems SVPlus sound velocimeter. Soundings were corrected for vessel motion using the Applanix POS/MV data, for variations in water-column sound velocity using the AM SVPlus data, and for variations in water height (tides) using vertical-position data from the KGPS receivers. Backscatter data from the 2006 and 2007 surveys (CSMP survey blocks CC-01, CC-02, CC-03, and CC-05) were processed using Geocoder Version 3.2 (Fugro Pelagos Modified Test Release 16). Within Geocoder, the backscatter intensities were radiometrically corrected (including despeckling and angle varying gain adjustments) and the position of each acoustic sample was geometrically corrected for slant range. After the lines were imported, they were mosaicked into a 1m resolution image. Overlap between parallel lines was resolved using a priority table based on the distance of each sample from the ship track, with samples closest to- and furthest from- the ship track given the lowest priority. An anti-aliasing algorithm was also applied.

    Person who carried out this activity:

    Carrie Bretz
    Seafloor Mapping Lab, California State University Monterey Bay
    Projects Manager, GIS; Metadata Supervisor
    100 Campus Center, Bldg 13
    Seaside, CA 93955
    USA

    (831) 582-4197 (voice)
    carrie_bretz@csumb.edu

    Date: 2011 (process 2 of 3)
    USGS received original Caris HIPS and SIPS projects from CSUMB of the 2004-2005 multibeam survey of the Entrance to San Francisco Bay. USGS re-processed the backscatter data using Caris Hips and Sips (version 7.1) integration of Geocoder. Within Geocoder, the backscatter intensities were radiometrically corrected (including despeckling and angle varying gain adjustments) and the position of each acoustic sample was geometrically corrected for slant range. After the lines were imported, they were mosaicked into a 1m resolution image. Overlap between parallel lines was resolved using a priority table based on the distance of each sample from the ship track, with samples closest to- and furthest from- the ship track given the lowest priority. An anti-aliasing algorithm was also applied.

    Person who carried out this activity:

    Mercedes Erdey
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Physical Scientist
    400 Natural Bridges Dr.
    Santa Cruz, CA 95060-5792
    USA

    (831) 460-7416 (voice)
    merdey@usgs.gov

    Date: 2011 (process 3 of 3)
    California Seafloor Mapping Project 1- and 2-m resolution backscatter imagery (CSMP survey blocks CC-01, CC-02, CC-03, and CC-05) within this map were downloaded from California State University, Monterey Bay, Seafloor Mapping Lab (<http://seafloor.csumb.edu/SFMLwebDATA.htm>) and converted to grids. Backscatter grids of similar mapping systems were merged in a GIS and clipped to the boundary of the map area. Grids from different mapping systems were not merged together due to different mapping frequencies and processing techniques.

    Person who carried out this activity:

    Pete Dartnell
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Physical Scientist
    400 Natural Bridges Dr.
    Santa Cruz, CA 95060-5792
    USA

    (831) 460-7415 (voice)
    pdartnell@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?

    Not applicable for raster data.

  2. How accurate are the geographic locations?

    Estimated to be no less than 2 m, owing to water depth and total propagated uncertainties of the mapping systems, which include sonar system, position and motion compensation system, and navigation, as well as data processing that includes sounding cleaning, gridding, and datum transformations.

  3. How accurate are the heights or depths?

    Not applicable to acoustic-backscatter imagery.

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

    Complete

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

    Unspecified


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:

USGS-authored or produced data and information are in the public domain. Acknowledge the U.S. Geological Survey and California State University, Monterey Bay, Seafloor Mapping Lab in products derived from these data. Share data products developed using these data with the U.S. Geological Survey.
This information is not intended for navigational purposes. Read and fully comprehend the metadata prior to data use. Uses of these data should not violate the spatial resolution of the data. Where these data are used in combination with other data of different resolution, the resolution of the combined output will be limited by the lowest resolution of all the data.
This database has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use
Although this Federal Geographic Data Committee-compliant metadata file is intended to document these data in nonproprietary form, as well as in ArcInfo format, this metadata file may include some ArcInfo-specific terminology.

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

    U.S. Geological Survey
    345 Middlefield Rd
    Menlo Park, CA 94025-3561
    USA

    (650) 329-4309 (voice)

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

  3. What legal disclaimers am I supposed to read?



    These databases, identified as acoustic-backscatter maps of Offshore of Pacifica, California have been approved for release and publication by the U.S. Geological Survey (USGS). Although these databases have been subjected to rigorous review and are substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.
    Although these data have been processed successfully on a computer system at the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein.
    Reference herein 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.
    These data are not intended for navigational use.

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: 02-Dec-2013
Last Reviewed: 02-Dec-2013
Metadata author:
Peter Dartnell
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Physical Scientist
400 Natural Bridges Dr.
Santa Cruz, CA 95060-5792
USA

(831) 460-7415 (voice)
(831) 427-4709 (FAX)
pdartnell@usgs.gov

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


Generated by mp version 2.9.16 on Wed Jan 21 09:56:33 2015