Time Series of Structure-from-Motion Products - Digital Elevation Models: Little Dauphin Island and Pelican Island, Alabama, September 2018 to April 2019

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Frequently anticipated questions:

What does this data set describe?

Title:
Time Series of Structure-from-Motion Products - Digital Elevation Models: Little Dauphin Island and Pelican Island, Alabama, September 2018 to April 2019
Abstract:
Aerial imagery acquired with a small unmanned aircraft system (sUAS), in conjunction with surveyed ground control points (GCP) visible in the imagery, can be processed with structure-from-motion (SfM) photogrammetry techniques to produce high-resolution orthomosaics, three-dimensional (3D) point clouds and digital elevation models (DEMs). This dataset, prepared by the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center (SPCMSC), provides UAS survey data products consisting of DEMs produced from imagery collected at Little Dauphin Island and Pelican Island, Alabama, from September 2018 to April 2019 in order to develop integrated models linking geomorphology, habitat characteristics, and non-breeding shorebird species usage.
Photogrammetry software was used to perform SfM processing on low-altitude digital aerial imagery acquired with a 3DR Solo UAS quadcopter equipped with a Ricoh GR II digital camera and MicaSense RedEdge 3 multispectral camera, using surveyed temporary targets (black and white, 4-square checked pattern) distributed uniformly throughout the UAS flight operations area as GCPs. The following SfM products are produced for each UAS survey over the northern half of Little Dauphin Island and all of Pelican Island: * georeferenced red-green-blue (RGB) orthomosaic image with 5-centimeter (cm) resolution * georeferenced multispectral (MS) orthomosaic image with 5-cm resolution * DEM with 5-cm horizontal resolution * 3D RGB-colored point cloud
All horizontal data are provided in the Universal Transverse Mercator (UTM) projected coordinate system, Zone 16 North (16N), referenced to the North American Datum of 1983 (NAD83(2011)), and elevation is referenced to the North American Vertical Datum of 1988 (NAVD88), GEOID12B.
Supplemental_Information:
These data were collected by the USGS Coastal and Marine Hazards and Resources Program under the following USGS field activity numbers (FANs), and the associated field activity web pages contain additional information regarding the field activity: 09/2018 FAN: 2018-352-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2018-352-FA ; 11/2018 FAN: 2018-362-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2018-362-FA ; 12/2018 FAN: 2018-370-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2018-370-FA ; 02/2019 FAN: 2019-306-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2019-306-FA ; 03/2019 FAN: 2019-311-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2019-311-FA ; 04/2019 FAN: 2019-317-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2019-317-FA .
  1. How might this data set be cited?
    Kranenburg, Christine J., Brown, Jenna A., Bosse, Stephen T., and Dalyander, P. Soupy, 20210610, Time Series of Structure-from-Motion Products - Digital Elevation Models: Little Dauphin Island and Pelican Island, Alabama, September 2018 to April 2019: U.S. Geological Survey Data Release doi:10.5066/P9I6BP66, U.S. Geological Survey, St. Petersburg, Florida.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.12889537
    East_Bounding_Coordinate: -88.10731142
    North_Bounding_Coordinate: 30.28187897
    South_Bounding_Coordinate: 30.23092080
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 12-Sep-2018
    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, 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: 16N
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -87
      Latitude_of_Projection_Origin: 0.0
      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 North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      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?
    Entity_and_Attribute_Overview:
    The DEM was exported as an encoded 32-bit floating point GeoTIFF, where each pixel has an explicit elevation value associated with it. The GeoTIFFs were created from the dense point cloud in Agisoft Photoscan with interpolation enabled. The no-data value is -32767.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Christine J. Kranenburg
    • Jenna A. Brown
    • Stephen T. Bosse
    • P. Soupy Dalyander
  2. Who also contributed to the data set?
    Data collection was funded by the U.S. Geological Survey. We would like to thank the following people for their contribution to the data collection efforts: Nicholas Enwright, Brett Patton, Chelsea Stalk, Nancy DeWitt and Sara Zeigler of the USGS, and Spencer Stelly of Stelly Consulting.
  3. To whom should users address questions about the data?
    Christine J. Kranenburg
    U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    ckranenburg@usgs.gov

Why was the data set created?

These SfM products were produced from aerial images collected at Little Dauphin and Pelican Islands, Alabama, from September 2018 to April 2019, in order to develop integrated models linking geomorphology, habitat characteristics, and non-breeding shorebird species usage.

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: 27-Aug-2019 (process 1 of 2)
    The SfM products were created for each UAS survey date individually, using the RGB digital negative (DNG) photos (Kranenburg and others, 2021). The complete set of photos was imported into Agisoft Photoscan (versions 1.3.5 - 1.5.5), along with corresponding ground control point reference information, and each flight was put into separate camera calibration groups. Photos were aligned at high accuracy, with a keypoint limit of 50,000 and unlimited tiepoints. Camera positions and the lens model were refined using three statistical metrics: reconstruction uncertainty, projection accuracy, and reprojection error with threshold values of 10, 2.6-3.0, and 0.3 respectively. Once the photo positions and lens models were optimized, dense point clouds were generated with Photoscan (Goncalves and Henriques, 2015) using the high quality and moderate filtering settings. The dense point clouds were then used to generate DEMs; note that the DEM represents the elevation of the surface as viewed from above (for example, tops of buildings and vegetation), and does not represent the bare earth surface. Person who carried out this activity:
    Christine J. Kranenburg
    U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
    Cartographer
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    ckranenburg@usgs.gov
    Date: 18-Dec-2020 (process 2 of 2)
    The DEMs were clipped to hand-digitized polygons of the island boundary and inland lagoons to remove as much erroneous data as possible. Person who carried out this activity:
    Christine J. Kranenburg
    U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
    Cartographer
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    ckranenburg@usgs.gov
  3. What similar or related data should the user be aware of?
    Kranenburg, C.J., Brown, J.A., Sturdivant, E.J., Stalk, C.A., Pendleton, E.A., and Ackerman, S.D., 2021, Time Series of True Color Aerial Imagery from Small Unmanned Aircraft Systems: Little Dauphin Island & Pelican Island, Alabama, September 2018 – April 2019: U.S. Geological Survey Data Release Unknown.

    Online Links:

    • Unknown

    Goncalves, J.A., and Henriques, R., 2015, UAV photogrammetry for topographic monitoring of coastal areas: ISPRS Journal of Photogrammetry and Remote Sensing vol. 104.

    Online Links:

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

  1. How well have the observations been checked?
    The horizontal and vertical measurements of the surface models were compared against global positioning system measurements of fixed features covered by the survey.
  2. How accurate are the geographic locations?
    The SfM-based geospatial products have an overall horizontal root-mean-square error (RMSE) of 3.4 cm, determined by comparing the horizontal position of the surveyed temporary check points (4-square, black and white, checkerboard targets) and the corresponding horizontal positions digitized in the orthomosaic, for all surveys.
  3. How accurate are the heights or depths?
    The SfM-based geospatial products have an overall vertical root-mean-square error (RMSE) of 3.3 cm, determined by comparing the surveyed check point elevations and the corresponding elevations in the DEM, for all check points from all surveys.
  4. Where are the gaps in the data? What is missing?
    This 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 fall within expected ranges, except points near and offshore of the waterline and in internal lagoons. Data in the point cloud near the waterline and over water bodies can be noisy and may result in erroneous measurements in the DEM, due to interpolation.

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 of the dataset and in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
    Attn: SPCMSC Data Management Group
    600 4th Street South
    St. Petersburg, FL
    USA

    727-502-8000 (voice)
    gs-g-spcmsc_data_inquiries@usgs.gov
  2. What's the catalog number I need to order this data set? These data are available in GeoTIFF format contained in a single ZIP file of SfM products per UAS survey. The DEM files are named with the following convention: yyyy-mm-IslandName-dem-5cm.tif where yyyy-mm represents the survey date as year (yyyy) and month (mm); IslandName can have a value of either LittleDauphinIsland or PelicanIsland; and ‘dem-5cm’ is used to designate the dataset as a 5-cm resolution DEM.
  3. What legal disclaimers am I supposed to read?
    This publication was prepared by an agency of the United States Government. Although these data were processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. 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?

Dates:
Last modified: 24-May-2021
Metadata author:
Christine J. Kranenburg
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
Cartographer
600 4th Street South
St. Petersburg, FL
USA

727-502-8000 (voice)
ckranenburg@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/CREMA_DEM_metadata.faq.html>
Generated by mp version 2.9.50 on Tue Sep 21 18:18:34 2021