Estero Bay, California, Acoustic Backscatter (Field Activity ID: S-05-12-SC)

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Frequently-anticipated questions:

What does this data set describe?

Estero Bay, California, Acoustic Backscatter (Field Activity ID: S-05-12-SC)
Between July 30 and August 09, 2012, scientists from the U.S. Geological Survey (USGS), Pacific Coastal and Marine Science Center (PCMSC), acquired bathymetry and acoustic-backscatter data from Estero Bay, San Luis Obispo, California, under PCMSC Field Activity ID S-05-12-SC. The survey was conducted using the R/V Parke Snavely outfitted with a multibeam sonar system for swath mapping and inertially-aided real-time kinematic navigation equipment for accurate georeferencing. This report provides these data in a number of different formats, as well as a summary of the mapping mission, maps of bathymetry and backscatter, and Federal Geographic Data Committee (FGDC) metadata.
The URL for USGS field activity S-05-12-SC is <>
  1. How should this data set be cited?

    U.S. Geological Survey (USGS), Pacific Coastal and Marine Science Cent, 2013, Estero Bay, California, Acoustic Backscatter (Field Activity ID: S-05-12-SC): U.S. Geological Survey Open-File Report 2013-1225.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -121.172404
    East_Bounding_Coordinate: -120.915074
    North_Bounding_Coordinate: 35.520167
    South_Bounding_Coordinate: 35.224352

  3. What does it look like?

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

    Beginning_Date: 30-Jul-2012
    Ending_Date: 09-Aug-2012
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: raster digital data

  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 16020 x 11456, type grid cell

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

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: 10
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000
      False_Northing: 0.0

      Planar coordinates are encoded using row and column
      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 World Geodetic System 1984 (G1150).
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.

      Altitude_Datum_Name: World Geodetic System 1984 (G1150)
      Altitude_Resolution: 0.01
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method: Attribute values

  7. How does the data set describe geographic features?

    Acoustic Bacscatter Amplitude
    Acoustic backscatter shows the relative strength of the acoustic signal returned from the seafloor. (Source: USGS)

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?

    USGS Pacific Coastal and Marine Science Center
    c/o Steve R Hartwell
    U.S. Geological Survey
    Santa Cruz, CA 95060

    (831) 460-7814 (voice)
    (831) 427-4748 (FAX)

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 to identify bathymetric features. This information is not intended for navigational purposes.

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-Jul-2012 (process 1 of 6)
    Sonar Data Collection
    Bathymetric surveys were completed using a RESON SeaBat 7111 multibeam echosounder. The sonar was pole-mounted on the 34-foot USGS mapping vessel R/V Parke Snavely. GNSS position and inertial motion and orientation measurement data were recorded using an Applanix Position and Orientation Solutions for Marine Vessels (POS MV) 320 inertial-aided position and orientation system. The sonar head, GNSS antennae, and the inertial motion unit (IMU) were surveyed in place to a common reference frame with a Geodimeter 640 Total Station. The R/V Parke Snavely was outfitted with three networked workstations and a navigation computer for use by the captain and survey crew for data collection and initial processing.

    Date: 09-Aug-2012 (process 2 of 6)
    Geodetic Control
    Geodetic control for the survey was established using the IN-Fusion SmartBase feature in the Applanix Position and Orientation System Post-Processing Package Mobile Mapping Suite (POSPac MMS, Version 6.1.4553.15282). IN-Fusion SmartBase is a feature in POSPac MMS that provides inertially-aided, carrier phase differential GNSS for mobile mapping platforms without requiring dedicated base receivers (Applanix, 2012). Instead, the software automatically selects a network of permanent GNSS reference stations accessible through the Internet and provides reference receiver coverage over the entire project area. The network of reference stations selected by the software changed slightly each day depending on the exact location of the survey vessel and the quality of the reference station data for the selected day.

    Date: 09-Aug-2012 (process 3 of 6)
    Vessel Position and Attitude
    The R/V Parke Snavely was equipped with a POS MV 320 system, which records inertial-motion and GNSS position data for the duration of the survey. The POS MV provides real-time pitch information to the multibeam sonar system to facilitate pitch-compensation (see discussion below). As discussed in the Geodetic Control Section, the GNSS data are combined with the inertial-motion measurements within the POSPac MMS software and high-precision position and attitude corrections are exported as SBET files for merging with the multibeam data.

    Date: 09-Aug-2012 (process 4 of 6)
    Sound Velocity Measurements
    Sound velocity measurements were collected continuously with an Applied Micro Systems Micro SV deployed on the transducer frame for real-time sound velocity adjustments at the transducer-water interface. The Micro SV is accurate to 0.03 m/s. In addition, sound velocity profiles (SVP) were collected with an Applied Micro Systems, SvPlus 3472. This instrument provided time-of-flight sound-velocity measurements by using invar rods with a sound-velocity accuracy of +/- 0.06 m/s, pressure was measured by a semiconductor bridge strain gauge to an accuracy of 0.15 percent (500 dbar, full scale), and temperature was measured by thermistor with an accuracy of 0.05 degrees Celsius.

    Date: 09-Aug-2012 (process 5 of 6)
    Sonar Sounding Processing
    CARIS HIPS and SIPS (version 7.1.0) bathymetry processing software was used to georeference the raw sonar data. The real-time attitude and position data was replaced with processed SBET data (described above); sound velocity corrections were applied; and the Total Propagated Uncertainty (TPU) for each sounding was estimated using Caris tools.

    Date: 18-Feb-2013 (process 6 of 6)
    Backscatter Image Production
    Acoustic backscatter data were processed using Fledermaus (QPS) FMGeocoder software package (version 7.3.2). Survey line bathymetry data were exported from the Caris HIPS and SIPS (version 7.1) acquisition software as GSF files. These line files were paired with the original backscatter lines files (s7K) and imported into the FMGeocoder software. Each line file was radiometrically corrected and adjusted for Angle Varying Gain (AVG) with the “Flat” option with a window size of 30. All processed line files were merged together into one overall 2-m resolution backscatter mosaic. The processed backscatter dB values for a number of lines were adjusted using the backscatter adjustment tool to better match surrounding backscatter dB values. This tool allows the user to manually adjust dB values over entire lines. Often, the dB values within a line changed abruptly causing the mosaic to look “patchy.” Due to this manual adjustment process and abrupt changes in dB values, the backscatter mosaic may be more useful for visual interpretations rather than empirical characterizations that compare pixel values over the entire mosaic. Once finalized, the backscatter mosaic was exported as a geoTIFF, imported in ESRI ArcGIS and converted to a grid.

  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?

    This bathymetric data has not been independently verified for accuracy.

  2. How accurate are the geographic locations?

    Uncertainty in the horizontal position of each sounding is a function of the total uncertainty propagated through each of the following component instruments: 1) vessel GPS, 2) intertial motion unit (IMU), 3) water sound velocity model, and 4) beam spreading in the water column. Assuming no systematic errors in the measurement instruments themselves, beam spreading is the dominate source of positional uncertainty. The 1.5-degree sonar beam of the SeaBat 7111 results in horizontal uncertainty ranging from 0.15 m at 10 m slant range, to about 0.70 m at 50 m slant range.

  3. How accurate are the heights or depths?

    After filtering the data to remove obvious outliers, the standard deviation of the remaining sounding elevations was calculated for each 2 m x 2 m and 4 m x 4 m cell (each containing an average of 5 soundings for each 2 m cell, and 12 soundings for each 4 m cell) in CARIS. The mean standard deviation for all cells in the Estero Bay survey is 0.12 m, and 95 percent of the cells in the data set have a standard deviation of less than 0.30 m.

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

    The 2012 mapping mission (U.S. Geological Survey (USGS) Field Activity ID: S-05-12-SC) collected high-resolution bathymetry and coregistered acoustic backscatter of outer Estero Bay, California. The survey was completed in 11 days, from July 30 to August 9, 2012, and consisted of 117 survey lines covering approximately 165 sq km in elevations ranging from about -45 m to -250 m relative to NAVD88. The survey extends from an existing bathymetric survey to approximately 15 km offshore with complete coverage within the area of interest.

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

    All bathymetric values are derived from the same instruments and processing workflow.

How can someone get a copy of the data set?

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

If physical samples or materials are available, constraints on their on-site access are described in "WR CMG Sample Distribution Policy" at URL: <>
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.

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

    U.S. Geological Survey, Pacific Coastal and Marine Science Center (PCMSC)
    c/o Steve Hartwell
    U.S. Geological Survey
    Santa Cruz, CA 95060-5792

    (831) 460-7814 (voice)
    (831) 427-4748 (FAX)

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

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    This information is not intended for navigational purposes.
    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.
    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.

  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 29-Jan-2013
Metadata author:
Pacific Coastal and Marine Science Center (PCMSC), US Geological Survey
U.S. Geological Survey
Santa Cruz, California 95060

(831) 460-7814 (voice)

Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

Generated by mp version 2.9.6 on Wed Nov 20 12:12:52 2013