Backscatter--Offshore of Refugio Beach Area, California

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What does this data set describe?

Title: Backscatter--Offshore of Refugio Beach Area, California
Abstract:

This part of SIM 3319 presents data for part of the acoustic-backscatter map (see sheet 3, SIM 3319) of Offshore Refugio Beach map area, California. The raster data file is included in "Backscatter_OffshoreRefugioBeach.zip," which is accessible from <https://pubs.usgs.gov/ds/781/OffshoreRefugioBeach/data_catalog_OffshoreRefugioBeach.html>.
The acoustic-backscatter map of Offshore Refugio Beach Area was generated from backscatter data collected by the U.S. Geological Survey (USGS). The USGS mapped this region in the summer 2008 using a 234.5 kHz SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonar. These data were later re-processed in 2012. 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, S-8-08-SC online at <http://walrus.wr.usgs.gov/infobank/s/s808sc/html/s-8-08-sc.meta.html>.
  1. How should this data set be cited?

    Dartnell, Peter, Phillips, Eleyne L., and Finlayson, David P., 2015, Backscatter--Offshore of Refugio Beach Area, 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., Krigsman, Lisa M., Dieter, Bryan E., Conrad, James E., Greene, H. Gary, Seitz, Gordon G., Endris, Charles A., Sliter, Ray W., Wong, Florence L., Erdey, Mercedes D., Gutierrez, Carlos I., Yoklavich, Mary M., Draut, Amy E., and Hart, Patrick E., 2015, California State Waters Map Series--Offshore of Refugio Beach Area, California: Scientific Investigations Map SIM 3319, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -120.19
    East_Bounding_Coordinate: -119.99
    North_Bounding_Coordinate: 34.55
    South_Bounding_Coordinate: 34.38

  3. What does it look like?

    <https://pubs.usgs.gov/ds/781/OffshoreRefugioBeach/images/Backscatter_OffshoreRefugioBeach.jpg> (JPEG)
    Acoustic backscatter imagery of offshore Refugio Beach.

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

    Calendar_Date: 2015
    Currentness_Reference: Publication Date

  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 NAVD88.
      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 Offshore Refugio Beach backscatter grid was originally archived as an ESRI grid with the following attributes: 
    Cell size = 2.0
Number of rows = 8960
Number of columns = 8960

Data type = floating point

Boundary
Xmin = 758070.0
Xmax = 775990.0
Ymin = 3808160.0
Ymax = 3826080.0

Statistics
Minimum value = 0
Maximum value = 65535.0
Mean = 32539.330
Standard deviation = 7803.45

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, Pacifc 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: 2008 (process 1 of 2)
    USGS backscatter data were collected in 2008 using a 234.5 kHz SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonar. During the USGS mapping mission, Real Time Kinematic (RTK) GPS data and measurements of vessel motion (heave, pitch, and roll) were combined in a CodaOctopus F190 attitude and position system to produce a high-precision vessel attitude packet. This packet was transmitted to the acquisition software in real time and combined with instantaneous sound-velocity measurements at the transducer head before each ping. The returned samples were projected to the seafloor using a ray-tracing algorithm working with previously measured sound-velocity profiles. Statistical filters were applied to the raw samples that discriminate the seafloor returns (soundings and backscatter) from other unintended targets in the water column.

    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

    Date: 2012 (process 2 of 2)
    Raw shipbord SWATHplus line files were post-processed using USGS software (D.P. Finlayson, 2011, written comm.) that normalizes for time-varying signal loss and beam directivity differences. Thus, the raw 16-bit backscatter data were gain-normalized to enhance the backscatter of the SWATHplus system. The resulting normalized-amplitude values were rescaled to 16-bit and gridded using GRID Processor Software, then imported into a GIS and converted to GRIDS.

    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:
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 U.S. Geological Survey 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: 29-Nov-2012
Last Reviewed: 29-Nov-2012
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 Mar 04 16:50:18 2015