Eelgrass distributions and bathymetry derived from an acoustic survey of the Nisqually River delta, Washington, 2017

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Frequently anticipated questions:

What does this data set describe?

Title:
Eelgrass distributions and bathymetry derived from an acoustic survey of the Nisqually River delta, Washington, 2017
Abstract:
This portion of the USGS data release presents eelgrass distribution and bathymetry data derived from acoustic surveys of the Nisqually River delta, Washington in 2017 (USGS Field Activity Number 2017-614-FA). Eelgrass and bathymetry data were collected from the R/V George Davidson equipped with a single-beam sonar system and global navigation satellite system (GNSS) receiver. The sonar system consisted of a Biosonics DT-X single-beam echosounder and 420 kHz transducer with a 6-degree beam angle. Depths from the echosounder were computed using sound velocity data measured using a YSI CastAway CTD during the survey. Positioning of the survey vessel was determined at 5 to 10 Hz using a Trimble R7 GNSS receiver and Trimble Zephyr Model 2 antenna operating in real time kinematic (RTK) mode. Differential corrections were transmitted by a VHF radio to the GNSS receiver on the survey vessel at 1-Hz from a GNSS base station placed on a nearby benchmark with known horizontal and vertical coordinates relative to the North American Datum of 1983 (CORS96 realization). Output from the GNSS and sonar systems were combined in real time by the Biosonics DT-X deck unit and output to a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing the vessel operator to navigate along predefined survey lines spaced at 25-50 m intervals alongshore at speeds of 2-3 m/s. Acoustic backscatter data were analyzed using a custom graphical user interface that implements a signal processing algorithm applied to each sonar sounding that differentiates and extracts the location of the seafloor apart from the presence of vegetation (Stevens and others, 2008). Individual acoustic returns along a survey line were grouped into packets of ten, and eelgrass percent cover was calculated as the fractional percent of acoustic returns that were classified as vegetated within each group, resulting in an estimate of percent cover every 4 to 5 m (depending on the vessel speed). Orthometric elevations relative to the NAVD88 vertical datum were computed using National Geodetic Survey Geoid12a offsets. The average estimated vertical uncertainty of the bathymetric measurements is 5 cm. The point data are provided in a comma-separated text file and are projected in Cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10 north, meters coordinate system.
Supplemental_Information:
Additional information about the field activities from which these data were derived are available online at:
https://cmgds.marine.usgs.gov/fan_info.php?fan=2017-614-FA
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  1. How might this data set be cited?
    Stevens, Andrew W., Takesue, Renee K., and Grossman, Eric E., 20200721, Eelgrass distributions and bathymetry derived from an acoustic survey of the Nisqually River delta, Washington, 2017: data release DOI:10.5066/P9N9K2I1, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    This is part of the following larger work.

    Stevens, Andrew W., Takesue, Renee K., and Grossman, Eric E., 2020, Eelgrass distributions and bathymetry of the Nisqually River delta, Washington: data release DOI:10.5066/P9N9K2I1, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -122.7526284
    East_Bounding_Coordinate: -122.6700898
    North_Bounding_Coordinate: 47.1220340
    South_Bounding_Coordinate: 47.0892620
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/5e95fcea82ce172707f25393?name=nq17_bathy_eelgrass_tracklines.png&allowOpen=true (PNG)
    Top: map showing bathymetry data along 2017 survey tracklines; Bottom: map showing eelgrass distribution and percent coverage along 2017 survey tracklines.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 20-Feb-2017
    Ending_Date: 23-Feb-2017
    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. It contains the following vector data types (SDTS terminology):
      • Point (1332887)
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0000001. Longitudes are given to the nearest 0.0000001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is North American Datum of 1983.
      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: 0.01
      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)
    datetime_utc
    The date and time of data collection in Coordinated Universal Time (UTC). (Source: Producer Defined)
    Range of values
    Minimum:2017-02-20 16:39:16.307
    Maximum:2017-02-23 23:44:15.642
    Units:date and time in yyyy-mmm-dd HH:MM:SS.FFF format
    longitude
    Longitude coordinate of data point relative to the North American Datum of 1983 (Source: Producer defined)
    Range of values
    Minimum:-122.7526284
    Maximum:-122.6700898
    Units:Decimal degrees
    latitude
    Latitude coordinate of data point relative to the North American Datum of 1983 (Source: Producer defined)
    Range of values
    Minimum:47.0892620
    Maximum:47.1220340
    Units:Decimal degrees
    easting_m
    East coordinate of data point relative to the North American Datum of 1983, projected in the Universal Transverse Mercator (UTM) Zone 10 North, meters, coordinate system (Source: Producer defined)
    Range of values
    Minimum:518764.99
    Maximum:525028.00
    Units:meters
    northing_m
    North coordinate of data point relative to the North American Datum of 1983,projected in the Universal Transverse Mercator (UTM) Zone 10 North, meters, coordinate system (Source: Producer defined)
    Range of values
    Minimum:5215119.52
    Maximum:5218755.75
    Units:meters
    elev_m_navd88
    Height in meters of data point with reference to the North American Vertical Datum of 1988 (Source: Producer defined)
    Range of values
    Minimum:-14.69
    Maximum:0.53
    Units:meters
    veg_flag
    Flag that indicates the presence or absence of eelgrass at each location along the survey track (Source: producer defined)
    ValueDefinition
    0eelgrass absent
    1eelgrass present
    veg_cover
    Fractional percent of points classified as vegetated grouped into packets of 10 sequential points (Source: Producer defined)
    Range of values
    Minimum:0.00
    Maximum:1.00
    Units:fractional percent

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
    • Renee K. Takesue
    • Eric E. Grossman
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    PCMSC Science Data Coordinator
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA

    831-427-4747 (voice)
    pcmsc_data@usgs.gov

Why was the data set created?

Data were obtained to document interannual changes in eelgrass distributions and coastal morphology following the removal of a dike that restored tidal processes to over 300 ha of former freshwater wetlands on the Nisqually River delta in 2009. 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 the distributions of eelgrass 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: 23-Feb-2017 (process 1 of 4)
    Eelgrass and bathymetry data were collected from the R/V George Davidson equipped with a single-beam sonar system and global navigation satellite system (GNSS) receiver. The sonar system consisted of a Biosonics DT-X single-beam echosounder and 420 kHz transducer with a 6-degree beam angle. Depths from the echosounder were computed using sound velocity data measured using a YSI CastAway CTD during the survey. Positioning of the survey vessel was determined at 5 to 10 Hz using a Trimble R7 GNSS receiver and Trimble Zephyr Model 2 antenna operating in real time kinematic (RTK) mode. Differential corrections were transmitted by a VHF radio to the GNSS receiver on the survey vessel at 1-Hz from a GNSS base station placed on a nearby benchmark with known horizontal and vertical coordinates relative to the North American Datum of 1983 (CORS96 realization). Output from the GNSS and sonar systems were combined in real time by the Biosonics DT-X deck unit and output to a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing the vessel operator to navigate along predefined survey lines spaced at 25-50 m intervals alongshore at speeds of 2-3 m/s.
    Date: 30-Mar-2017 (process 2 of 4)
    Acoustic-backscatter data were analyzed using a custom graphical user interface that implements a signal processing algorithm applied to each sonar sounding to extract the location of the bottom and presence of vegetation (Stevens and others, 2008). Individual acoustic returns along a survey line were grouped into packets of ten, and eelgrass percent cover was calculated as the fractional percent of acoustic returns that were classified as vegetated within each group, resulting in an estimate of percent cover every 4 to 5 m (depending on the vessel speed). Orthometric elevations relative to the NAVD88 vertical datum were computed using National Geodetic Survey Geoid12a offsets. The final point data are provided in a comma-separated text file and are projected in Cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10 north, meters coordinate system.
    Date: 09-Apr-2020 (process 3 of 4)
    All available eelgrass distribution and bathymetry data from the survey were compiled into a comma-delimited text file for distribution.
    Date: 19-Oct-2020 (process 4 of 4)
    Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?
    Stevens, Andrew W., Lacy, Jessica R., Finlayson, David P., and Gelfenbaum, Guy, 2008, Evaluation of a single-beam sonar system to map seagrass at two sites in northern Puget Sound, Washington: U.S. Geological Survey, Reston, VA.

    Online Links:

    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?
    Survey-grade positions of the survey vessel were achieved with a global navigation satellite system (GNSS) differentially corrected with data from a single GNSS base station placed on a benchmark with horizontal coordinates relative to the North American Datum of 1983 (CORS96 realization). The position of the GNSS base station was derived from a static GNSS occupation on February 21, 2012 with a duration of approximately 4 hours. The static observations were processed using the National Geodetic Survey Online Positioning User Service (OPUS) to derive the final base station coordinates. The estimated uncertainty derived from the static occupation was 2 cm and 3.5 cm for the latitude and longitude of the benchmark, respectively. Additional uncertainty in the horizontal positions of the survey vessel was estimated based on the distance between survey vessel and GNSS base station. Manufacturer reported accuracy for the differentially corrected horizontal positions for the GNSS rover trajectories is 0.8 cm + 0.5 ppm. Baselines from the GNSS base station varied between 50 m and 4.5 km with a mean of 1.75 km, suggesting the average horizontal accuracy of survey vessel positions to be about 1 cm. Combining the uncertainty in the benchmark and survey vessel yields a total uncertainty of 5 cm. Uncertainty in the horizontal positions associated with pitch and roll of the survey vessel 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. The vertical position of the benchmark was derived from a static GNSS occupation with an estimated uncertainty of 3.9 cm. The manufacturer-reported accuracy for the differentially corrected vertical positions for the GNSS rover trajectories is 1.5 cm + 1 ppm relative to the benchmark elevation. Baselines from the GNSS base station varied between 50 m and 4.5 km with a mean of 1.75 km, suggesting the average vertical accuracy of survey vessel positions to be about 1.7 cm. The manufacturer of the single-beam echosounder used in this study reports a vertical accuracy of 1 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, is depth-dependent. Based on analysis of available speed of sound measurements, we estimate uncertainties in the final depth soundings to be no greater than 1 percent of the water depth. The total vertical uncertainty is calculated using the constant- and depth-dependent factors summed in quadrature (International Hydrographic Organization, 2008). The vertical uncertainty in final elevations varied between 4 cm and 16 cm with a mean estimated vertical uncertainty of 5 cm. Uncertainty in the vertical positions associated with pitch and roll of the survey vessel 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? Eelgrass distribution and bathymetry data are available as a comma-delimited text file, along with associated FGDC-compliant metadata and a browse graphic.
  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: 19-Oct-2020
Metadata author:
PCMSC Science Data Coordinator
U.S. Geological Survey, Pacific Coastal and Marine Science Center
2885 Mission St.
Santa Cruz, CA

831-427-4747 (voice)
pcmsc_data@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/DataReleases/ScienceBase/DR_P9N9K2I1/nq17_bathy_eelgrass_metadata.faq.html>
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