Nearshore bathymetry data from the Elwha River delta, Washington, April 2014, collected from personal watercraft

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Frequently anticipated questions:


What does this data set describe?

Title:
Nearshore bathymetry data from the Elwha River delta, Washington, April 2014, collected from personal watercraft
Abstract:
This part of the data release presents bathymetry data from the Elwha River delta collected in April 2014 using two personal watercraft (PWCs). The PWCs were equipped with single-beam echosounders and survey-grade global navigation satellite system (GNSS) receivers.
Supplemental_Information:
Additional information about the field activities from which these data were derived are available online at: http://cmgds.marine.usgs.gov/fan_info.php?fan=2014-620-FA
  1. How might this data set be cited?
    Stevens, Andrew W., Gelfenbaum, Guy, Warrick, Jonathan A., Miller, Ian M., and Weiner, Heather M., 2017, Nearshore bathymetry data from the Elwha River delta, Washington, April 2014, collected from personal watercraft: data release DOI:10.5066/F76T0JSP, U.S. Geological Survey, Santa Cruz, CA.

    Online Links:

    This is part of the following larger work.

    Stevens, Andrew W., Gelfenbaum, Guy, Warrick, Jonathan A., Miller, Ian M., and Weiner, Heather M., 2017, Bathymetry, topography, and sediment grain-size data from the Elwha River delta, Washington, April and May 2014: data release DOI:10.5066/F76T0JSP, U.S. Geological Survey, Santa Cruz, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -123.586931
    East_Bounding_Coordinate: -123.413227
    North_Bounding_Coordinate: 48.158893
    South_Bounding_Coordinate: 48.132058
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 26-Apr-2014
    Ending_Date: 29-Apr-2014
    Currentness_Reference:
    ground condition at time data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: comma-delimited text
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set.
    2. What coordinate system is used to represent geographic features?
      The map projection used is Lambert Conformal Conic.
      Projection parameters:
      Standard_Parallel: 47.5
      Standard_Parallel: 48.73333333333333
      Longitude_of_Central_Meridian: -120.8333333333333
      Latitude_of_Projection_Origin: 47.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.001
      Ordinates (y-coordinates) are specified to the nearest 0.001
      Planar coordinates are specified in METERS
      The horizontal datum used is NAD83 (CORS96).
      The ellipsoid used is GRS_1980.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222101.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: 0.001
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:
      Explicit elevation coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    Attribute Table
    Table containing attribute information associated with the dataset (Source: Producer defined)
    Survey_Date
    The date corresponding to the start of the multi-day survey in mm/dd/yyyy format (Source: Producer Defined)
    Range of values
    Minimum:04/26/2014
    Maximum:04/26/2014
    Units:date in mm/dd/yyyy format
    Longitude
    Longitude coordinate of data point relative to the North American Datum of 1983 (CORS96 realization) (Source: Producer defined)
    Range of values
    Minimum:-123.586931
    Maximum:-123.413227
    Units:Decimal degrees
    Latitude
    Latitude coordinate of data point relative to the North American Datum of 1983 (CORS96 realization) (Source: Producer defined)
    Range of values
    Minimum:48.132058
    Maximum:48.158893
    Units:Decimal degrees
    X
    East coordinate of data point relative to the North American Datum of 1983 (CORS96 realization), projected in the Washington State Plane, North, meters, coordinate system (Source: Producer defined)
    Range of values
    Minimum:295138.773
    Maximum:308052.364
    Units:meters
    Y
    North coordinate of data point relative to the North American Datum of 1983 (CORS96 realization), projected in the Washington State Plane, North, meters, coordinate system (Source: Producer defined)
    Range of values
    Minimum:129308.320
    Maximum:132432.476
    Units:meters
    Ellip_Ht_m
    Height in meters of data point with reference to the reference ellipsoid (Source: Producer defined)
    Range of values
    Minimum:-45.341
    Maximum:-18.964
    Units:meters
    Ortho_Ht_m
    Height in meters of data point with reference to the North American Vertical Datum of 1988 at the base station (-20.11 m above ellipsoid height). (Source: Producer defined)
    Range of values
    Minimum:-25.231
    Maximum:1.146
    Units:meters

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Andrew W. Stevens
    • Guy Gelfenbaum
    • Jonathan A. Warrick
    • Ian M. Miller
    • Heather M. Weiner
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Andrew W. Stevens
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission St.
    Santa Cruz, CA
    USA

    831-460-7424 (voice)
    astevens@usgs.gov

Why was the data set created?

Data were obtained to assess the coastal geomorphic response following the removal of two dams on the Elwha River. 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 topographic and shallow-water bathymetric features.

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: 29-Apr-2014 (process 1 of 3)
    Bathymetry data were collected between April 26 and April 29, 2014 using two identical single-beam sonar systems and global navigation satellite systems (GNSS) receivers mounted on personal watercraft (PWC). The sonar systems consisted of an Odom Echotrac CV-100 single-beam echosounder and 200 kHz transducer with a 9-degree beam angle. Raw acoustic backscatter returns were digitized by the echosounder with a vertical resolution of 1.25 cm. Depths from the echosounders were computed using sound velocity profiles measured using a YSI CastAway CTD during the survey. Positioning of the survey vessels was determined at 10-Hz using Trimble R7 GNSS receivers with Trimble Zephyr Model 2 antennas operating primarily in real-time kinematic (RTK) mode. Differential corrections were transmitted by a VHF radio to the PWC GNSS receivers at 1-Hz from a base station placed on a benchmark with known horizontal and vertical coordinates relative to the North American Datum of 1983 (CORS96 realization) and North American Vertical Datum of 1988. Output from the GNSS and sonar systems were combined in real time on the PWC by a computer running HYPACK (version 13.0.0.6) hydrographic survey software. Navigation information was displayed on a video monitor, allowing PWC operators to navigate along survey lines at speeds of 2 to 3 m/s.
    Date: 12-May-2014 (process 2 of 3)
    Positioning data from the GNSS were collected primarily in real-time kinematic (RTK) mode. Poor radio communication in some portions of the survey area prevented acquisition of RTK data. GNSS positioning data that were collected in autonomous mode were post-processed using Waypoint Grafnav (version 8.50.4320) to apply differential corrections from the base station GNSS receiver. Elevations relative to the NAVD88 vertical datum were computed using a static offset of -20.11 m based on the National Geodetic Survey Geoid09 offset computed at the base-station locations. Bathymetry data were merged with GNSS positions, and quality control was applied using the computer program transectViewer, a Graphical User Interface (GUI) programmed with the computer program MATLAB. Digitized depths were compared to the raw acoustic-backscatter signal to ensure accuracy of depths produced by the echosounder, and the GUI was used to digitize the bottom by hand where the echosounder signal processing failed, as was typical in areas with submerged aquatic vegetation. After the raw depths were adjusted, a running mean with a window length of 5 points (approximately 1 m distance) was used to remove high-frequency vertical fluctuations, such as those caused by pitch and roll of the survey vessels. The final data are projected in Cartesian coordinates using the Washington State Plane North, meters coordinate system.
    Date: 08-Dec-2016 (process 3 of 3)
    All available bathymetry data from the survey were compiled into a comma-delimited text file for distribution
  3. What similar or related data should the user be aware of?
    International Hydrographic Organization (IHO), 2008, IHO standards for hydrographic surveys (5th ed.): International Hydrographic Bureau Special Publication 44, 28p., Monaco.

    Online Links:


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    No formal attribute accuracy tests were conducted
  2. How accurate are the geographic locations?
    A series of benchmarks with known coordinates were established adjacent to the study area to provide geodetic control for the bathymetric surveys. The positions of the benchmarks were derived from a minimum of two static GNSS occupations. The equipment for the static occupations consisted of a dual frequency Trimble R7 GNSS receiver, a fixed-height tripod, and Trimble Geodetic Model 2 antenna. The static observations were recorded internally in the receiver and the raw observations were processed using the National Geodetic Survey Online Positioning User Service (OPUS, https://www.ngs.noaa.gov/OPUS/). Estimated uncertainties in the horizontal position of the individual GNSS occupations were provided by OPUS and ranged between 0.006 m and 0.06 m with an average horizontal uncertainty of 0.02 m. The processed positions from each occupation were averaged to obtain the final reported position of the benchmark. All final positions of the survey vessels were determined using differential corrections from the base station receivers. Manufacturer reported accuracy for the differentially corrected horizontal positions for the Trimble R7 rover trajectories is 0.8 cm + 0.5 ppm. Baselines from the GNSS base station were typically less than 5 km, suggesting a horizontal accuracy of survey-vessel positions to be 0.825 cm. The combined horizontal uncertainty from the base station coordinate solutions and rover trajectories is between 1.5 cm and 7 cm, with a mean horizontal uncertainty of 3 cm. Uncertainty in the horizontal positions associated with pitch and roll of the survey vessels is unknown.
  3. How accurate are the heights or depths?
    Uncertainty in the final elevations is derived from the combination of uncertainty in the GNSS positioning and bathymetric sounding measurements. Manufacturer reported accuracy for the differentially corrected vertical positions for the Trimble R7 rover trajectories is 1.5 cm + 1 ppm. Baselines from the GNSS base station were typically less than 5 km, suggesting the vertical accuracy of survey vessel positions to be 2 cm relative to the base station coordinate. Combining the uncertainty in the elevation of the base station coordinates and rover positions yields a total uncertainty in the GNSS-derived survey-vessel positions of approximately 5 cm. Additional uncertainty in the final computed elevations data is related to unmeasured variability in the speed of sound used to compute depths from bathymetric soundings and, thus, are depth-dependent. Based on analysis of all available speed of sound measurements, we estimate uncertainties in the final depth soundings to be 0.6 percent of the water depth. The total vertical uncertainty is calculated using Equation 1: sigmat=sqrt(a^2+(b×d)^2), where sigmat is the total vertical uncertainty, a is the uncertainty of the GNSS vertical position, b is the depth-dependent uncertainty factor (0.006), and d is water depth (International Hydrographic Organization, 2008). Maximum water depths surveyed on this mapping mission are approximately 18 m yielding a maximum total vertical uncertainty of 12 cm. Uncertainty in the vertical positions associated with pitch and roll of the survey vessels is unknown.
  4. Where are the gaps in the data? What is missing?
    Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    All data falls within expected ranges.

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 from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data. This information is not intended for navigational purposes.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - Science Base
    U.S. Geological Survey
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO
    USA

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? Bathymetry data are available as a comma-delimited text file (ew14_apr_pwc.txt), along with associated metadata.
  3. What legal disclaimers am I supposed to read?
    Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by 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.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 08-Dec-2016
Metadata author:
Andrew W. Stevens
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Oceanographer
2885 Mission St.
Santa Cruz, CA
USA

831-460-7424 (voice)
astevens@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/westcoast/washington/elwha/ew14_apr_pwc.faq.html>
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