Backscatter B [USGS]--Offshore of Ventura, California

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Frequently-anticipated questions:

What does this data set describe?

Title: Backscatter B [USGS]--Offshore of Ventura, California
Abstract:
This part of SIM 3254 presents data for part of the acoustic-backscatter map (see sheet 3, SIM 3254) of the Offshore Ventura map area, California. The raster data file is included in "BackscatterB_USGS_OffshoreVentura.zip," which is accessible from <https://pubs.usgs.gov/ds/781/OffshoreVentura/data_catalog_OffshoreVentura.html>. The acoustic-backscatter map of the Offshore Ventura map area, California, was generated from backscatter data collected by California State University, Monterey Bay, Seafloor Mapping Lab (CSUMB) and by the U.S. Geological Survey (USGS). These metadata describes the acoustic-backscatter data collected by the USGS (see "BackscatterA_CSUMB_OffshoreVentura_metadata.txt" metadata for a description of the acoustic-backscatter data collected by CSUMB). The seafloor west of Ventura Harbor was mapped by the USGS in 2006 and 2010, using 117-kHz (2006) and 234.5-kHz (2010) SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonars. These mapping missions collected acoustic-backscatter data from about the 10-m isobath to beyond the 3-nautical-mile limit of California's State Waters. Within the acoustic-backscatter 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 sediment type. 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).
Supplemental_Information:
Information for the related USGS Pacific Coastal and Marine Science Center data collection field activities, Z-2-06-SC online at <http://walrus.wr.usgs.gov/infobank/z/z206sc/html/z-2-06-sc.meta.html> and S-W1-09-SC online at <http://walrus.wr.usgs.gov/infobank/s/sw109sc/html/s-w1-09-sc.meta.html>.
  1. How should this data set be cited?

    Dartnell, Peter, Kvitek, Rikk G. , Phillips, Eleyne L. , and Cochrane, Guy R. , 2013, Backscatter B [USGS]--Offshore of Ventura, California:.

    This is part of the following larger work.

    Johnson, Samuel Y. , Dartnell, Peter, Cochrane, Guy R. , Golden, Nadine E. , Phillips, Eleyne L. , Ritchie, Andrew C. , Kvitek, Rikk G. , Greene, H. Gary , Krigsman, Lisa M. , Endris, Charles A. , Seitz, Gordon G. , Gutierrez, Carlos I. , Sliter, Ray W. , Erdey, Mercedes D. , Wong, Florence L. , Yoklavich, Mary M. , Draut, Amy E. , Hart, Patrick E. , and Cochran, Susan A. , 2013, California State Waters Map Series--Offshore of Ventura, California: Scientific Investigations Map SIM 3254, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -119.44
    East_Bounding_Coordinate: -119.25
    North_Bounding_Coordinate: 34.38
    South_Bounding_Coordinate: 34.22

  3. What does it look like?

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

    Beginning_Date: 2006
    Ending_Date: 2010
    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: 11
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -117.00000
      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 USGS 2006 backscatter grid was originally archived as an ESRI grid with the following attributes: 
    Cell size = 2.0
Number of rows = 3623
Number of columns = 3643

Data type = floating point

Boundary
Xmin = 284123.00
Xmax = 291409.00
Ymin = 3787799.00
Ymax = 3795045.00

Statistics
Minimum value = 0
Maximum value = 255
Mean = 194.32
Standard deviation = 62.68

Coordinate system description
Projection  UTM
Zone  11
Datum  WGS84
Units  meter
    The USGS 2010 backscatter grid was originally archived as an ESRI grid with the following attributes: 
    Cell size = 2.0
Number of rows = 3235
Number of columns = 1995

Data type = floating point

Boundary
Xmin = 283431.00
Xmax = 287421.00
Ymin = 3784973.00
Ymax = 3791443.00

Statistics
Minimum value = 0
Maximum value = 254
Mean = 118.11
Standard deviation = 33.31

Coordinate system description
Projection  UTM
Zone  11
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: 2011 (process 1 of 1)
    USGS acoustic-backscatter data were collected in 2006 and 2010, using 117-kHz (2006) and 234.5-kHz (2010) SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonars aboard the USGS R/V Parke Snavely. The survey vessel was equipped with a CodaOctopus F180 attitude and position system. This system combines differential GPS data (2006) and real time kinematic GPS data (2-centimeter error ellipse) (2010) with inertial motion measurements so that high-precision position and attitude corrections are fed in real-time to the sonar acquisition equipment. Up to 10 pings per second are transmitted, each ping consisting of 2,048 samples per side (port and starboard). The returned samples are projected to the seafloor using a ray-tracing algorithm working with the previously measured sound-velocity profiles. A series of statistical filters are applied to the raw samples that discriminate the seafloor returns from other unintended targets in the water column. The raw 16-bit backscatter data recorded simultaneously with bathymetry by the SWATHplus was georeferenced and gain-normalized by the program SXPEGN, software written by the USGS to enhance the backscatter of the SWATHplus system. The program normalizes for time-varying signal loss and beam-directivity differences. The resulting normalized-amplitude values are rescaled to 16-bit and gridded into a GeoJPEG image using GRID Processor Software supplied by SEA. The GeoJPEG was imported into a GRID using ESRI GIS software and clipped to the Offshore of Ventura map area boundary.

    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 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

  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:
Please recognize the U.S. Geological Survey (USGS) and California State University, Monterey Bay, Seafloor Mapping Lab (CSUMB). USGS-authored or produced data and information are in the public domain. 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. Acknowledge the USGS and CSUMB in products derived from these data. Share data products developed using these data with the U.S. Geological Survey. 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.

Who wrote the metadata?

Dates:
Last modified: 15-Mar-2013
Last Reviewed: 15-Mar-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 2.9.6 on Tue Jul 09 17:32:27 2013