Digital elevation model of Little Holland Tract, Sacramento-San Joaquin Delta, California, 2015

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Frequently anticipated questions:


What does this data set describe?

Title:
Digital elevation model of Little Holland Tract, Sacramento-San Joaquin Delta, California, 2015
Abstract:
This product is a digital elevation model (DEM) for the Little Holland Tract in the Sacramento-San Joaquin River Delta, California based on U.S. Geological Survey (USGS)-collected elevation data, merged with existing topographic and bathymetric elevation data. The USGS collected topographic and bathymetric elevation data in 2015, using a combination of methods. Topographic and shallow-water bathymetric data were collected on foot using a global positioning system (GPS) backpack platform that consisted of survey-grade Trimble R10, and Trimble R7 global navigation satellite system (GNSS) receivers with Zephyr 2 antennas. Bathymetric data were collected using a personal watercraft (PWC) platform that consisted of Trimble R7 GNSS receivers with Zephyr 2 antennas, combined with Odom Echotrac CV-100 single-beam echosounders and 200 kHz transducers. The USGS elevation data were merged with topographic aerial Light Detection and Ranging (lidar) data collected by California Department of Water Resources (DWR) in 2007 and single-beam bathymetric data collected by Environmental Data Solutions (EDS) in 2009 to generate the final DEM. The GeoTIFF raster and comma-delimited text files are available for download at http://dx.doi.org/10.5066/F7RX9954.
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=2015-642-FA
  1. How might this data set be cited?
    USGS, 2016, Digital elevation model of Little Holland Tract, Sacramento-San Joaquin Delta, California, 2015: data release DOI:10.5066/F7RX9954, U.S. Geological Survey, Santa Cruz, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -121.671678053
    East_Bounding_Coordinate: -121.642613237
    North_Bounding_Coordinate: 38.352223681
    South_Bounding_Coordinate: 38.280295064
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 01-Jan-2007
    Currentness_Reference:
    ground condition at time data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: digital raster and 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 Raster data set. It contains the following raster data types:
      • Dimensions 7948 x 2426 x 1, 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: -123.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 1.0
      Ordinates (y-coordinates) are specified to the nearest 1.0
      Planar coordinates are specified in Meter
      The horizontal datum used is D_North_American_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.
  7. How does the data set describe geographic features?
    Attribute Table
    Table containing attribute information associated with the data set. (Source: Producer defined)
    Value
    Elevation (NAVD88) (Source: Producer defined)
    Range of values
    Minimum:-9.7361621856689
    Maximum:13.201800346375
    Units:meters
    Entity_and_Attribute_Overview:
    The entity and attribute information provided here describes the tabular data associated with the data set. Please review the detailed descriptions that are provided (the individual attribute descriptions) for information on the values that appear as fields/table entries of the data set.
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information was generated by the individual and/or agency identified as the originator of the data set. Please review the rest of the metadata record for additional details and information.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • USGS
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Attn: Jessica R Lacy
    Research Oceanographer
    2885 Mission St.
    Santa Cruz, CA

    831-460-7520 (voice)
    831-427-4748 (FAX)
    jlacy@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 to identify topographic and bathymetric features.

How was the data set created?

  1. From what previous works were the data drawn?
    bathy (source 1 of 5)
    Snyder, Alexander G., Stevens, Andrew W., Carlson, Emily, and Lacy, Jessica R., 2016, Bathymetric measurements of Little Holland Tract, Sacramento-San Joaquin Delta, California, 2015, from personal watercraft: U.S. Geological Survey, Santa Cruz, CA.

    Online Links:

    Type_of_Source_Media: digital dataset
    Source_Contribution:
    Bathymetry data were combined with topography data, and then interpolated into a gridded surface. See Process Steps for details.
    topo (source 2 of 5)
    Snyder, Alexander G., Stevens, Andrew W., Carlson, Emily, and Lacy, Jessica R., 2016, Topographic measurements of Little Holland Tract, Sacramento-San Joaquin Delta, California, 2015, using backpack GPS: U.S. Geological Survey, Santa Cruz, CA.

    Online Links:

    Type_of_Source_Media: digital dataset
    Source_Contribution:
    Topography data were combined with bathymetry data, and then interpolated into a gridded surface. See Process Steps for details.
    EDS 2009 (source 3 of 5)
    Solutions, Environmental Data, 200905, West Delta Condition Bathymetric Surveys: Field Data collection Procedures. Prepared for CBEC Inc.: Environmental Data Solutions, San Rafael, CA.

    Type_of_Source_Media: Digital and/or Hardcopy Resources
    Source_Contribution:
    Bathymetry data were combined with topography data, and then interpolated into a gridded surface. See Process Steps for details.
    DWR 2007 (source 4 of 5)
    California Department of Water Resources, 2007, 2007 Sacramento-San Joaquin Delta LiDAR Acquisition: NOAA's Ocean Service, Office for Coastal Management, Sacramento, CA.

    Online Links:

    Type_of_Source_Media: Digital and/or Hardcopy Resources
    Source_Contribution:
    Topography data were combined with bathymetry data, and then interpolated into a gridded surface. See Process Steps for details.
    NOAA 2012 (source 5 of 5)
    National Oceanic and Atmospheric Administration (NOAA), 2012, 2012 NOAA Ortho-rectified Color Mosaic of Sacramento Deep Water Ship Channel, California: National Oceanic and Atmospheric Administration (NOAA), Silver Spring, MD.

    Type_of_Source_Media: Digital and/or Hardcopy Resources
    Source_Contribution: used for shoreline digitizing
  2. How were the data generated, processed, and modified?
    Date: 01-Oct-2015 (process 1 of 1)
    The elevation data collected by the USGS during this survey were combined with existing data to generate a digital elevation model (DEM). Additional data sources were used to model the topography of the exposed areas of Little Holland Tract and the bathymetry of the surrounding channels. Topographic aerial Light Detection and Ranging (lidar) data (DWR, 2009) were used to generate the DEM in the areas where land is exposed. The lidar dataset required some processing, which included removing returns from water and vegetation. The effect of vegetation was reduced by using the minimum elevation in a 2-meter grid space. Additionally, bathymetric data from 2009 (EDS, 2009) were used to estimate the bathymetry of the channels surrounding Little Holland Tract, and the shoreline was digitized using an aerial photo (NOAA, 2012). The elevation of this shoreline was estimated by averaging the elevation values collected using backpack GPS systems in areas where the survey was spatially coincident with the digital shoreline. Combining the three datasets, USGS 2015 elevation data, DWR 2007 LiDAR, and CBEC 2009 bathymetry, a triangular irregular network (TIN) was generated using ArcMap 10.2.2, using the digitized shoreline as a hard breakline. The TIN was then converted to a grid with 1-meter resolution. Data sources used in this process:
    • all sources cited were used
  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 during the USGS 2015 elevation survey, but no comparisons to "true" values were conducted. Accuracy of additional data sources could not be assessed.
  2. How accurate are the geographic locations?
    The Digital Elevation Model (DEM) was created by interpolating between measurements as much as 100 meters apart, for this reason we cannot evaluate the accuracy of each point in the DEM, only the measurements it is based on. The lidar collected by California Department of Water Resources stated a horizontal accuracy of 1 meter. The bathymetric data collected by Environmental Data Solutions (2009) did not report horizontal accuracy. Accuracy estimates for the PWC survey platforms were estimated by computing the standard deviations of the GNSS rover positions relative to the static base station using Waypoint Grafnav (version 5.0). Based on these calculations, the mean horizontal accuracy of GNSS positions at the 95 percent confidence interval (1.96 times the standard deviations assuming a normal distribution) is 3.5 cm. Accuracy estimates for the GPS Backpack survey platforms were based on horizontal precision values calculated in Trimble Business Center. Horizontal precision values for each point are included in the dataset, but overall the minimum, maximum, mean and standard deviation precision calculations were 0.009, 0.103, 0.0239, and 0.006 meters, respectively.
  3. How accurate are the heights or depths?
    The Digital Elevation Model (DEM) was created by interpolating between measurements as much as 100 meters apart, for this reason we cannot evaluate the accuracy of each point in the DEM, only the measurements it is based on. The lidar collected by California Department of Water Resources stated a vertical accuracy of 18.5 cm. The bathymetric data collected by Environmental Data Solutions (2009) did not report a vertical accuracy. Accuracy estimates for the PWC survey platforms were estimated by computing the standard deviations of the GNSS rover positions relative to the static base station using Waypoint Grafnav (version 5.0). Based on these calculations, the mean vertical accuracy of GNSS positions at the 95 percent confidence interval (1.96 times the standard deviations assuming a normal distribution) were calculated. Depths measured using sonar are subject to additional sources of uncertainty including fluctuations in the speed of sound and from the pitch and roll of the survey vessels. Given the relatively calm water surface and low range of water depth present in this survey, we estimate depth sounding uncertainty to be 1 percent of the water depth. The mean estimated vertical uncertainty is 6.1 cm. Accuracy estimates for the GPS Backpack survey platforms were based on vertical precision values calculated in Trimble Business Center. Vertical precision values for each point are included in the dataset, but overall the minimum, maximum, mean and standard deviation precision calculations were 0.194, 0.014, 0.0351, and 0.011 meters, respectively.
  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?
    Data falls within expected ranges. Efforts were made during digital elevation modeling to best represent reality.

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 - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? The digital elevation model (DEM) is available as both a comma-delimited text file (LHT15_dem.txt), along with a zip file (LHT15_dem.zip) that contains a GeoTIFF, as well 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. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 08-Mar-2017
Metadata author:
Jessica R Lacy
U.S. Geological Survey, Pacific Coastal and Marine Science Center
2885 Mission St.
Santa Cruz, CA

831-460-7520 (voice)
831-427-4748 (FAX)
jlacy@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/sf_bay_delta/LHT15_dem_FGDC.faq.html>
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