Topography data from the Elwha River delta, Washington, July 2015

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Frequently anticipated questions:


What does this data set describe?

Title:
Topography data from the Elwha River delta, Washington, July 2015
Abstract:
This part of the data release presents topography data from the Elwha River delta collected in July 2015. Topography data were collected on foot with global navigation satellite system (GNSS) receivers mounted on backpacks.
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=2015-648-FA
  1. How might this data set be cited?
    Stevens, Andrew W., Gelfenbaum, Guy, Warrick, Jonathan A., Miller, Ian M., and Weiner, Heather M., 2016, Topography data from the Elwha River delta, Washington, July 2015: data release DOI:10.5066/F7S75DG9, 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., 2016, Bathymetry, topography, and sediment grain-size data from the Elwha River delta, Washington, July 2015: data release DOI:10.5066/F7S75DG9, U.S. Geological Survey, Santa Cruz, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -123.641406
    East_Bounding_Coordinate: -123.472108
    North_Bounding_Coordinate: 48.152323
    South_Bounding_Coordinate: 48.131690
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 29-Jul-2015
    Ending_Date: 31-Jul-2015
    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 data set (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:07/29/2015
    Maximum:07/29/2015
    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:-123.641406
    Maximum:-123.472108
    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:48.131690
    Maximum:48.152323
    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:291099.480
    Maximum:303640.540
    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:129274.820
    Maximum:131717.260
    Units:meters
    Ellip_Ht_m
    Height in meters of data point with reference to the reference ellipsoid (Source: Producer defined)
    Range of values
    Minimum:-21.710
    Maximum:-14.080
    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:-1.600
    Maximum:6.030
    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: 31-Jul-2015 (process 1 of 2)
    Topography data were collected between July 29 and July 31, 2015 on foot with GNSS equipment mounted on backpacks operating primarily in real-time kinematic (RTK) mode. A total of 5 GNSS backpacks, each equipped with a dual-frequency GNSS receiver and handheld data collector, were used during the survey. Differential corrections were transmitted at 1-Hz intervals by a VHF radio to the backpack GNSS receivers from a GNSS 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. Prior to data collection, vertical distances between the GNSS antenna and the ground were measured using a tape measure for each topographic surveyor. Hand-held data collectors were used to log raw data and display navigational information allowing surveyors to navigate along predefined survey lines spaced at 25- to 50-m intervals along the delta. Profiles were surveyed from the landward edge of the primary dune over the beach foreshore, to wading depth on the same series of transects as the nearshore bathymetry platforms. Additional topography data were collected between transects to better characterize morphologic variability within the study area.
    Date: 31-Aug-2015 (process 2 of 2)
    Raw topography data were reviewed in either Trimble Geomatics Office (TGO) or Trimble Business Center (TBC) to ensure measured antenna offsets were applied properly in the field. Differential post-processing was performed on points collected in autonomous mode where VHF communication with the base station failed. All available topography data were compiled and exported in comma-separated text file for distribution.
  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?
    Repeatability tests were conducted across different survey platforms, but no comparisons to "true" values 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 and topographic 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 (NGS) 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 GNSS backpacks were determined using differential corrections from the base station receivers. Manufacturer reported accuracy for the differentially corrected horizontal positions for the Trimble R7, R8, and R10 receivers used in the survey is 0.8 cm + 0.5 ppm. Baselines from the GNSS base station were typically less than 5 km, suggesting a horizontal accuracy of backpack positions to be 0.825 cm relative to the base station. The combined horizontal uncertainty from the base station coordinate solutions and rover trajectories is therefore approximately 3 cm. Uncertainty in the horizontal positions associated with variable posture during data collection of the surveyors is unknown.
  3. How accurate are the heights or depths?
    The vertical uncertainty of topographic measurements is estimated by combining the uncertainty in the base station coordinate and remote GNSS positions collected in kinematic mode. Uncertainties in the elevation of the base station were provided by NGS OPUS and ranged between 0.02 m and 0.04 m, with an average vertical uncertainty of 0.03 m. Manufacturer reported vertical accuracy in the rover positions is 1.5 cm + 1 ppm for differential corrected kinematic data for the Trimble R7, R8 and R10 receivers used in the surveys. Baseline lengths were typically less than 5 km, suggesting the vertical accuracy of backpack positions to be 2 cm relative to the base station coordinates. Combining the uncertainty in the elevation of the base station coordinates and rover positions yields a total uncertainty in the backpack GNSS positions of approximately 5 cm. Uncertainty in the vertical positions associated with variable posture of the surveyors during data collection 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? Topography data are available as a comma-delimited text file (ew15_july_topo.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: 16-Nov-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/ew15_july_topo.faq.html>
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