Digital Elevation Models

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Frequently anticipated questions:

What does this data set describe?

Title: Digital Elevation Models
Abstract:
This data release presents structure-from-motion (SFM) products derived from aerial imagery surveys with precise Global Navigation Satellite System (GNSS) navigation data flown in a piloted fixed wing aircraft taken along the North Carolina coast in response to Hurricane Florence (available here https://coastal.er.usgs.gov/data-release/doi-P91KB9SF/). USGS researchers use the elevation models and orthorectified imagery to assess future coastal vulnerability, nesting habitats for wildlife, and provide data for hurricane impact models. The products span the coast over both highly developed towns and natural areas, including federal lands. These products represent the coast after Hurricane Florence and cover the Cape Fear area, North Carolina to the Virginia border vicinity from October 6-8, 2018. This research is part of the Remote Sensing Coastal Change Project.
Supplemental_Information:
The raw imagery and navigation data used to produce the DEMs are available online at https://coastal.er.usgs.gov/data-release/doi-P91KB9SF/. Bounding coordinates are derived from the overall flight path and are not necessarily representative of individual DEM bounds which are split up along the coast to have more accessible data download sizes.
  1. How might this data set be cited?
    U.S. Geological Survey, 20210602, Digital Elevation Models: data release DOI:10.5066/P9CA3D8P, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Ritchie, Andrew C., Over, Jin-Si R., Kranenburg, Christine J., Brown, Jenna A., Buscombe, Daniel, Sherwood, Christopher R., Warrick, Jonathan A., and Wernette, Phillipe A., 2021, Aerial Photogrammetry Data and Products of the North Carolina Coast: 2018-10-06 to 2018-10-08, Post-Hurricane Florence: data release DOI:10.5066/P9CA3D8P, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    suggested citation: Ritchie, A.C., Over, J.R., Kranenburg, C.J., Brown, J.A., Buscombe, D., Sherwood, C.R., Warrick, J.A., and Wernette, P.A, 2021. Aerial Photogrammetry Data and Products of the North Carolina Coast— 2018-10-06 to 2018-10-08, Post-Hurricane Florence: U.S Geological Survey data release, https://doi.org/10.5066/P9CA3D8P
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -78.1859
    East_Bounding_Coordinate: -75.4576
    North_Bounding_Coordinate: 36.2213
    South_Bounding_Coordinate: 33.8365
  3. What does it look like?
    "DEM_example_BrowseImage.jpg" https://www.sciencebase.gov/catalog/file/get/6037d8fbd34eb12031175191?f=__disk__bd%2F0f%2F5a%2Fbd0f5aeeeb87f8798c2ea14861324d4fc7a17d56&allowOpen=true (JPEG)
    Example height-colored digital elevation model example image from 2018-10-07.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 06-Oct-2018
    Ending_Date: 08-Oct-2018
    Currentness_Reference:
    ground condition, data was collected on three days: October 6, 7, and 8 of 2018.
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data (GeoTIFF)
  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 Pixel
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 18
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -69.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 1
      Ordinates (y-coordinates) are specified to the nearest 1
      Planar coordinates are specified in meters
      The horizontal datum used is NAD83_National_Spatial_Reference_System_2011.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
      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:
    Pixels represent elevation in meters relative to NAVD88, the no-data value is -99999. There are 15 DEM 32-bit floating point cloud optimized GeoTIFFs. The filename for each DEM is formatted as "date_location_to_location_1m_UTM18N_NAVD88_cog.tif", where date is the date the images were collected (in YYYYMMDD format), location_to_location is the specific geographic location in North Carolina of the northern extent to the southern extent (for example Beaufort_Inlet_to_Bogue_Inlet), 1m indicates the resolution of the grid, UTM18N_NAVD88 denotes the horizontal and vertical reference systems, and cog denotes the product is a cloud optimized GeoTIFF. The horizontal projection is in NAD83(2011) UTM Zone 18N for all DEMs, even though one of the sections is partially in Zone 17N.
    Entity_and_Attribute_Detail_Citation: USGS

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
    Data collection was funded by the U.S Geological Survey. Data acquisition was conducted by Wayne Wright LLC. Data processing was done by the U.S Geological Survey.
  3. To whom should users address questions about the data?
    Andrew C Ritchie
    U.S. Geological Survey, SOUTHWEST REGION
    Geologist
    2885 Mission Street
    Santa Cruz, CA
    US

    831-460-7454 (voice)
    831-427-4748 (FAX)
    aritchie@usgs.gov

Why was the data set created?

The digital elevation models (DEMs) estimate the land surface after Hurricane Florence and were created to document interannual changes in shoreline position and coastal morphology in response to storm events using aerial imagery collections and a structure-from-motion (SFM) workflow. 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?
    Aerial Imagery (source 1 of 2)
    Kranenburg, Christine, Ritchie, Andrew C, Brown, Jennifer (Jenna) A, Over, Jin-Si R, Buscombe, Daniel, Sherwood, Christopher R, Warrick, Jonathan, and Wernette, Phillipe A, 2020, Post-Hurricane Florence Aerial Imagery: Cape Fear to Duck, North Carolina, October 6-8, 2018: U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: The data in this release are used to make SFM products.
    Ground Control Points (source 2 of 2)
    Jennifer (Jenna) A. Brown, Sherwood, Christopher R., Martini, Marinna, Kranenburg, Christine J., and Over, Jin-Si R., 2021, Ground Control Point Data from the Outer Banks, North Carolina, post-Hurricane Dorian, September 2019.

    Online Links:

    Type_of_Source_Media: Digital and/or Hardcopy
    Source_Contribution: The Ground Control Points are used in the SFM process.
  2. How were the data generated, processed, and modified?
    Date: Jan-2021 (process 1 of 2)
    On a workstation (AMD Threadripper 3960X /AsRock TRX40 Creator motherboard/256GB 3000MHz RAM) using Win10x64, all Aerial Imagery (and associated positional data) and 21 of 34 available Ground Control Points were brought into an Agisoft Metashape Pro (v. 1.6.5) project based on identification in the imagery. Only one ground control point, #34, was used as a control point to help 'lock' in the camera positions whereas the rest of the points were used as check points. See the Aerial Imagery citation metadata for Metashape Reference Settings inputs. To align in a 4D manner (see Sherwood and others, 2018) additional imagery and positions were added from 2019-08-30, 2019-09-02, 2019-09-08, 2019-09-12, and 2019-09-13 (see contact person below for imagery data, in publication prep). The additional imagery improves the horizontal and vertical accuracy but are not used past this initial alignment process step; similar products can be reproduced without them. The following steps were performed on the Metashape project in the geographic coordinate system NAD83(2011) in ellipsoid height following the general guidance of Over and others (2021): 1. Separate camera models and camera groups were created for each flight date. 2. Imagery (with positions) are aligned to create a point cloud using a 'High' alignment setting, keypoint limit of 70,000, tiepoint limit of 0, generic preselection selected, and reference preselection via source selected. The tiepoint accuracy was set to 1 pixel. 3. The resultant point cloud was filtered using one iteration of the 'Reconstruction uncertainty' filter at a level of 10, one iteration of the 'Projection accuracy' filter at a level of 3, and two iterations of the 'Reprojection accuracy' filer at a level of 0.3 (in the second iteration the 'fit additional corrections' option was turned on). With each filter iteration points are selected, deleted, and then the camera model optimized to refine the focal length, cx, cy, k1, k2, k3, p1, and p2 camera model coefficients. 4. Natural breaks in the final alignment product were identified based on bodies of water or the extreme northern and southern ends of a flight (see PostFlorence_InletMap.jpg on the larger citation landing page https://www.sciencebase.gov/catalog/item/6037cc78d34eb1203117512d). These 'chunks' are the vicinity of the Virginia-North Carolina border (VA is used to denote this northern extent) to Oregon Inlet, Oregon Inlet to Hattaras Inlet, Hattaras Inlet to Ocracoke Inlet, Ocracoke Inlet to Ophelia Inlet, Ophelia Inlet to Beaufort Inlet, Beaufort Inlet to Bogue Inlet, Bogue Inlet to New River Inlet, and New River Inlet to Oak Island. For each chunk all aligned images and associated tie points in that section were kept and the remainder deleted.
    Sherwood, C.R., Warrick, J.A., Hill, A.D., Ritchie, A.C., Andrews, B.D. and Plant, N.G., 2018. Rapid, remote assessment of Hurricane Matthew impacts using four-dimensional structure-from-motion photogrammetry. Journal of Coastal Research, 34(6), pp.1303-1316. Person who carried out this activity:
    Andrew C Ritchie
    U.S. Geological Survey, SOUTHWEST REGION
    Geologist
    2885 Mission Street
    Santa Cruz, CA
    US

    831-460-7454 (voice)
    831-427-4748 (FAX)
    aritchie@usgs.gov
    Data sources used in this process:
    • Aerial Imagery
    • Ground Control Points
    Date: Feb-2021 (process 2 of 2)
    From the previous process step, each 'chunk' is processed as follows to create the final DEM products for each flight date: 1. All imagery from October 6, 7, and 8 in the aligned chunk is copied from the workstation to a new Agisoft Metashape Pro. project on the U.S Geological Survey Tallgrass high-performance computing network for processing on CPU and GPU nodes (https://www.usgs.gov/core-science-systems/sas/arc/machine-access). 2. If multiple flight dates were flown for this chunk, imagery from one date is targeted, and the rest are disabled (this is then switched for each flight date in the chunk after the final step and steps 3- repeated) 3. A high quality dense point cloud is generated for the chunk with 'mild' filtering and the options to calculate point color and point confidence selected. 4. Dense point cloud is filtered using the 'Filter by Confidence' tool using the range 0-2, these points selected at this range are classified as low noise. 5. A DEM is built from the dense point cloud with interpolation disabled and without the points classified as low noise. 6. DEM is exported in NAD83(2011) UTM Zone 18N and NAVD88(meters) with 1 meter cell size and region boundaries rounded to the nearest 10 meter interval. West and south bounds are rounded up and east and north bounds are rounded down. 7. DEM is clipped by a shapefile in ArcMap (v. 10.7.1) to remove high uncertainty regions near waterlines. Uncertainty is visualized using a hillshade of the DEM with an elevation factor of 5 and an additional filter that highlights areas with a high standard deviation away from the overall elevation values. The shapefile is created and edited by hand with help from the corresponding orthorectified product. 8. Final clipped DEM is turned into a Cloud Optimized GeoTIFF (COG) using gdal_translate with the following command:for %i in (.\*.tif) do gdal_translate %i .\cog\%~ni_cog.tif -of COG -stats -co BLOCKSIZE=256 -co COMPRESS=LZW -co PREDICTOR=YES -co NUM_THREADS=ALL_CPUS -co BIGTIFF=YES (v. 3.1.4 accessed October 20, 2020 https://gdal.org/). Where i is the name of each geoTIFF section. Person who carried out this activity:
    Andrew C Ritchie
    U.S. Geological Survey, SOUTHWEST REGION
    Geologist
    2885 Mission Street
    Santa Cruz, CA
    US

    831-460-7454 (voice)
    831-427-4748 (FAX)
    aritchie@usgs.gov
  3. What similar or related data should the user be aware of?
    Over, Jin-Si R., Ritchie, Andrew C., Kranenburg, Christine, Jennifer (Jenna) A. Brown, Buscombe, Daniel, Noble, Tom, Sherwood, Christopher R., Warrick, Jonathan, and Wernette, Phillipe, 2021, Processing coastal imagery with Agisoft Metashape Professional Edition, version 1.6—Structure from motion workflow documentation: Open File Report 2021-1039, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    This publication includes the general methodology for processing imagery in Metashape to produce DEMs and ortho products.

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

  1. How well have the observations been checked?
    The source imagery and positional information and metadata that were used to create these photogrammetrically derived digital elevation models are available here: https://coastal.er.usgs.gov/data-release/doi-P91KB9SF/ Information on the horizontal and vertical accuracies of the source data can be found within the data release metadata.
  2. How accurate are the geographic locations?
    The horizontal positional accuracy was evaluated against 21 of the 34 independent photo-identifiable ground control points measured with survey-grade GPS (Brown and others, 2021 - see citation below in lineage for additional accuracy report) but 20 (#'s 5, 6, 8, 12-16, 18-20, 22, 24, 26-29, 31, and 33) were used as check points and only 1 control point (#32) from the Outer Banks and the post-processed kinematic (PPK) camera positions (Kranenburg and others, 2020 - see citation below in lineage for additional accuracy report) were used to create the final DEM products. As reported by the software Agisoft Metashape Professional, the SFM project after alignment that creates the DEMs had an overall GCP control point horizontal root-mean-square error (RMSE) of 5.18 cm and the total camera position horizontal RMSE was 25.19 cm. The horizontal accuracy for each individual DEM is reported in the Digital Forms section.
  3. How accurate are the heights or depths?
    The vertical positional accuracy was evaluated against 21 of the 34 independent photo-identifiable ground control points measured with survey-grade GPS (Brown and others, 2021 - see citation below in lineage for additional accuracy report) but 20 (#'s 5, 6, 8, 12-16, 18-20, 22, 24, 26-29, 31, and 33) were used as check points and only 1 control point (#32) from the Outer Banks and the post-processed kinematic (PPK) camera positions (Kranenburg and others, 2020 - see citation below in lineage for additional accuracy report) were used to create the final DEM products. As reported by the software Agisoft Metashape Professional, the SFM project after alignment has an overall GCP control point vertical root-mean-square error (RMSE) of 24.63 cm and the total camera position vertical RMSE was 11.20 cm. The vertical accuracy for each individual DEM after alignment and error reduction and is reported in the Digital Forms section. The digital elevation models were also compared to a published joint Airborne Lidar Bathymetry Technical Center of eXpertise (JALBTCX) dataset with first returns (that include vegetation) flown specifically after Hurricane Florence (available from https://www.fisheries.noaa.gov/inport/item/57345) and the overall vertical differences are within the estimated vertical accuracy of the lidar (19.6 centimeters).
  4. Where are the gaps in the data? What is missing?
    These products cover the coast from near Duck to near Oak Island, North Carolina. Of the 37,497 raw images used in the SFM process 35,920 images were left after alignment and error reduction processes to create these DEMs. The final DEM products are not interpolated and have been cropped to remove noise and zones of high uncertainty in the foreshore, offshore, and near clustered buildings, therefore the DEMs do not cover the same exact extent as the associated orthorectified products available in this larger work citation. 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?
    The dense cloud was edited (see processing steps) to remove erroneous points from the surface before constructing the elevation model. All data fall into expected ranges except for points near tall buildings, areas of poorer image overlap, and near to offshore of the waterline, where the data return is often sparse, noisy, and erroneous. The DEM includes returns from the vegetation canopy.

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:
Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information.
  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
    United States

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? The 15 DEM cloud optimized GeoTIFFS are available in 1-m resolution stored with LZW compression and represent the coast of North Carolina after Hurricane Florence on October 6, 7, and 8, 2018. The first file from north to south on October 6, 2018 is 20181006_VA_to_Oregon_Inlet_1m_UTM18N_NAVD88_cog.tif (160MB), the horizontal RMSE is 33.907 cm and the vertical RMSE is 10.370 cm. The second file from north to south on October 6, 2018 is 20181006_Oregon_Inlet_to_Hatteras_Inlet_1m_UTM18N_NAVD88_cog.tif (230MB), the horizontal RMSE is 32.508 cm and the vertical RMSE is 19.330 cm. The third file from north to south on October 6, 2018 is 20181006_Hatteras_Inlet_to_Ocracoke_Inlet_1m_UTM18N_NAVD88_cog.tif (66MB), the horizontal RMSE is 116.566 cm and the vertical RMSE is 13.251 cm. The fourth file from north to south on October 6, 2018 is 20181006_Ocracoke_Inlet_Ophelia_Inlet_1m_UTM18N_NAVD88_cog.tif (99MB), the horizontal RMSE is 27.577 cm and the vertical RMSE is 11.818 cm. The fifth and last file from north to south on October 6, 2018 is 20181006_Ophelia_Inlet_to_Beaufort_Inlet_1m_UTM18N_NAVD88_cog.tif (80MB), the horizontal RMSE is 29.775 cm and the vertical RMSE is 17.485 cm. The first file from north to south on October 7, 2018 is 20181007_Oregon_Inlet_to_Hatteras_Inlet_1m_UTM18N_NAVD88_cog.tif (40MB), the horizontal RMSE is 7.714 cm and the vertical RMSE is 6.959 cm. The second file from north to south on October 7, 2018 is 20181007_Hatteras_Inlet_to_Ocracoke_Inlet_1m_UTM18N_NAVD88_cog.tif (57MB), the horizontal RMSE is 9.153 cm and the vertical RMSE is 5.990 cm. The third file from north to south on October 7, 2018 is 20181007_Ocracoke_Inlet_Ophelia_Inlet_1m_UTM18N_NAVD88_cog.tif (138MB), the horizontal RMSE is 9.969 cm and the vertical RMSE is 5.794 cm. The fourth file from north to south on October 7, 2018 is 20181007_Ophelia_Inlet_to_Beaufort_Inlet_1m_UTM18N_NAVD88_cog.tif (119MB), the horizontal RMSE is 9.905 cm and the vertical RMSE is 6.632 cm. The fifth file from north to south on October 7, 2018 is 20181007_Beaufort_Inlet_to_Bogue_Inlet_1m_UTM18N_NAVD88_cog.tif (62MB), the horizontal RMSE is 8.920 cm and the vertical RMSE is 5.710 cm. The sixth file from north to south on October 7, 2018 is 20181007_Bogue_Inlet_to_New_River_Inlet_1m_UTM18N_NAVD88_cog.tif (43MB), the horizontal RMSE is 7.158 cm and the vertical RMSE is 8.297 cm. The seventh and last file from north to south on October 7, 2018 is 20181007_New_River_Inlet_Oak_Island_1m_UTM18N_NAVD88_cog.tif (488MB), the horizontal RMSE is 9.990 cm and the vertical RMSE is 7.172 cm. The first file from north to south on October 8, 2018 is 20181008_VA_to_Oregon_Inlet_1m_UTM18N_NAVD88_cog.tif (154MB), the horizontal RMSE is 11.223 cm and the vertical RMSE is 7.264 cm. The second file from north to south on October 8, 2018 is 20181008_Oregon_Inlet_to_Hatteras_Inlet_1m_UTM18N_NAVD88_cog.tif (224MB), the horizontal RMSE is 10.244 cm and the vertical RMSE is 7.867 cm. The third and last file from north to south on October 8, 2018 is 20181008_Hatteras_Inlet_to_Ocracoke_Inlet_1m_UTM18N_NAVD88_cog.tif (60MB), the horizontal RMSE is 10.812 cm and the vertical RMSE is 6.498 cm.
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of these data or related materials. Any use of trade, product, or firm 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: 02-Jun-2021
Metadata author:
Jin-Si Over
U.S. Geological Survey
geographer
384 Woods Hole Rd.
Woods Hole, MA

508-548-8700 x2269 (voice)
jover@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P9CA3D8P/FloSup_2018-10-NC_DEMs.faq.html>
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