Coastal Topography—Assateague Island, Maryland and Virginia, Post-Hurricane Hermine, 10-12 September 2016

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Frequently anticipated questions:


What does this data set describe?

Title:
Coastal Topography—Assateague Island, Maryland and Virginia, Post-Hurricane Hermine, 10-12 September 2016
Abstract:
A digital elevation model (DEM) mosaic was produced for Assateague Island, Maryland and Virginia, post-Hurricane Hermine, from remotely sensed, geographically referenced elevation measurements collected by Quantum Spatial using a Riegl VQ-880-G (532-nm wavelength circular scan and 1064-nm wavelength linear scan) lidar sensor.
Supplemental_Information:
Processed data products are used by the U.S. Geological Survey CMGP's National Assessment of Coastal Change Hazards project to quantify the vulnerability of shorelines to coastal change hazards such as severe storms, sea-level rise, and shoreline erosion and retreat.
  1. How might this data set be cited?
    U.S. Geological Survey, 20170324, Coastal Topography—Assateague Island, Maryland and Virginia, Post-Hurricane Hermine, 10-12 September 2016: U.S. Geological Survey Data Series doi:10.5066/F7NP22NH, U.S. Geological Survey, St. Petersburg, FL.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -75.40368708
    East_Bounding_Coordinate: -75.08583525
    North_Bounding_Coordinate: 38.32613127
    South_Bounding_Coordinate: 37.84866877
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 10-Sep-2016
    Ending_Date: 12-Sep-2016
    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?
      Indirect_Spatial_Reference: Tiling Index
      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: -75.000000
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.000000
      False_Northing: 0
      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 1.00000
      Ordinates (y-coordinates) are specified to the nearest 1.00000
      Planar coordinates are specified in meters
      The horizontal datum used is North American Datum of 1983 (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 1/298.25722210100002.
      Vertical_Coordinate_System_Definition:
      Altitude_System_Definition:
      Altitude_Datum_Name: North American Vertical Datum of 1988 (GEOID12B)
      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?

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?
    Acknowledgment of the U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, as a data source would be appreciated in products developed from these data, and such acknowledgment as is standard for citation and legal practices for data source is expected. Sharing of new data layers developed directly from these data would also be appreciated by the U.S. Geological Survey staff. Users should be aware that comparisons with other datasets for the same area from other periods may be inaccurate because of inconsistencies resulting from changes in photointerpretation, mapping conventions, and digital processes over time. These data are not legal documents and are not to be used as such.
  3. To whom should users address questions about the data?
    Xan Fredericks
    U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
    Cartographer/Lidar Coordinator
    600 4th Street South
    St. Petersburg, FL
    USA

    727 502-8086 (voice)
    727 502-8182 (FAX)
    afredericks@usgs.gov
    Hours_of_Service: M-F, 8:00-4:00 ET

Why was the data set created?

The purpose of this project was to produce a highly detailed and accurate digital elevation map for Assateague Island, Maryland and Virginia for use as a management tool and to make these data available to natural-resource managers and research scientists. To ensure that SPCMSC data management protocols were followed, this survey was assigned a USGS field activity number (FAN), 16CNT03. Additional survey and data details are available at http://cmgds.marine.usgs.gov/fan_info.php?fan=16CNT03. USGS Contract: G16PC00016 Task Order Number: G16D01063

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: 30-Nov-2016 (process 1 of 5)
    Quantum Spatial reports the following steps for Lidar Pre-Processing: 1. Review flight lines and data to ensure complete coverage of the study area and positional accuracy of the laser points. 2. Resolve kinematic corrections for aircraft position data using kinematic aircraft GPS and static ground GPS data. 3. Develop a smoothed best estimate of trajectory (SBET) file that blends post-processed aircraft position with sensor head position and attitude recorded throughout the survey. 4. Calculate laser point position by associating SBET position to each laser point return time, scan angle, intensity, etc. Create raw laser point cloud data for the entire survey in *.las format. Convert data to orthometric elevations by applying a geoid correction. 5. Import raw laser points into manageable blocks to perform manual relative accuracy calibration and filter erroneous points. Apply the refraction correction necessary for bathymetric data. Classify ground/bathymetric points for individual flight lines. 6. Using ground classified points per each flight line, test the relative accuracy. Perform automated line-to-line calibrations for system attitude parameters (pitch, roll, heading), mirror flex (scale) and GPS/IMU drift. Calculate calibrations on ground classified points from paired flight lines and apply results to all points in a flight line. Use every flight line for relative accuracy calibration. 7. Adjust the point cloud by comparing ground classified points to supplemental ground control points. Person who carried out this activity:
    Quantum Spatial
    517 SW 2nd Street, Suite 400
    Corvallis, OR
    USA

    541-752-1204 (voice)
    541-752-3770 (FAX)
    Hours_of_Service:
    Monday through Friday 8:30 AM to 5:00 PM (Pacific Standard Time)
    Data sources used in this process:
    • Base_Station_Control, SBETs, SGCPs, RAW_LiDAR
    Date: 30-Nov-2016 (process 2 of 5)
    Quantum Spatial reports the following steps for Lidar Post-Processing: 1. Classify data to ground and other client designated classifications using proprietary classification algorithms. 2. Manually QC data classification 3. After completion of classification and final QC approval, calculate density information and verify final accuracy calculations for the project using ground control quality check points. Person who carried out this activity:
    Quantum Spatial
    517 SW 2nd Street, Suite 400
    Corvallis, OR
    USA

    541-752-1204 (voice)
    541-752-3770 (FAX)
    Hours_of_Service:
    Monday through Friday 8:30 AM to 5:00 PM (Pacific Standard Time)
    Data sources used in this process:
    • Base_Station_Control, SBETs, QCPs, RAW_LiDAR
    Data sources produced in this process:
    • Classified_LiDAR
    Date: 30-Nov-2016 (process 3 of 5)
    Quantum Spatial reports the following steps for Breaklines: Water boundary polygons were developed using manual editing techniques. Elevations were assigned to the water’s edge from the LiDAR point cloud data. Breaklines were also used to classify water surface (class 41). Person who carried out this activity:
    Quantum Spatial
    517 SW 2nd St., Suite 400
    Corvallis, OR
    USA

    541-752-1204 (voice)
    541-752-3770 (FAX)
    Hours_of_Service:
    Monday through Friday 8:30 AM to 5:00 PM (Pacific Standard Time)
    Data sources used in this process:
    • Classified_LiDAR
    Data sources produced in this process:
    • Breaklines
    Date: 30-Nov-2016 (process 4 of 5)
    Quantum Spatial reports the following steps for Bathymetric Coverage: Bathymetric coverage was determined by triangulating bathymetric points (class 40) with and edge length maximum of 4.56m to identify all areas >9m2 lacking bathymetric data. This shapefile was used to control the extent of the topobathymetric DEMs. Person who carried out this activity:
    Quantum Spatial
    517 SW 2nd St., Suite 400
    Corvallis, OR
    USA

    541-752-1204 (voice)
    541-752-3770 (FAX)
    Hours_of_Service:
    Monday through Friday 8:30 AM to 5:00 PM (Pacific Standard Time)
    Data sources used in this process:
    • Classified_LiDAR
    Data sources produced in this process:
    • Breaklines
    Date: 28-Dec-2016 (process 5 of 5)
    The provided DEM .IMG files were mosaicked using Global Mapper 16 (20160309) and exported as a GeoTIFF. Person who carried out this activity:
    Xan Fredericks
    U.S. Geological Survey, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
    Cartographer/lidar Coordinator
    600 4th Street South
    St. Petersburg, FL
    USA

    727 502-8086 (voice)
    afredericks@usgs.gov
    Hours_of_Service: M-F, 8:00-4:00 ET
  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?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
    Quantum Spatial reports that the contract specifications required that only Nonvegetated Vertical Accuracy (NVA) were computed for raw lidar point cloud swath files. The vertical accuracy was tested with 13 independent surveys located in open terrain. These check points were not used in the calibration or post-processing of the lidar point cloud data. The survey check points were distributed throughout the project area. The independent check points were surveyed using the closed level loop technique. Elevations from the unclassified lidar surface were measured for the x,y location of each check point. Elevations interpolated from the lidar surface were then compared to the elevation values of the surveyed control. The Root Mean Square Error (RMSE) was computed to be 0.042. AccuracyZ has been tested as 0.082 meters AccuracyZ at 95 percent Confidence Interval, meeting 19.6 cm NVA at 95 percent confidence level using (RMSEz * 1.9600) as defined by the National Standards for Spatial Data Accuracy (NSSDA); assessed and reported using National Digital Elevation Program (NDEP)/American Society of Photogrammetry and Remote Sensing (ASPRS) Guidelines.
  4. Where are the gaps in the data? What is missing?
    Quantum Spatial reports that the LAS files used to create the DEM include all data points collected. No points have been removed or excluded. Shaded relief images have been visually inspected for data errors such as pits, border artifacts, and shifting. Lidar flight lines have been examined to ensure consistent elevation values across overlapping flight lines. The raw point cloud is of good quality and data passes Vertical Accuracy specifications.
  5. How consistent are the relationships among the observations, including topology?
    Quantum Spatial reports that data cover the entire area specified for this project, approximately 52,196.2 acres. "NoData" values correspond with lack of submerged and/or bare-earth data within the survey bounds.

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. The U.S. Geological Survey requests to be acknowledged as originator of these data in future products or derivative research.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    Attn: Xan Fredericks
    Cartographer/Lidar Coordinator, U.S. Geological Survey
    600 4th Street South
    St. Petersburg, FL
    USA

    727 502-8086 (voice)
    Hours_of_Service: M-F, 8:00-4:00 ET
  2. What's the catalog number I need to order this data set? ASIS2016_HRHM_SM_z18_n88g12B_mosaic.tif
  3. What legal disclaimers am I supposed to read?
    Although these data have been processed successfully on a computer system at the 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. The USGS shall not be held liable for improper or incorrect use of the data described and/or contained herein. 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?
  5. Is there some other way to get the data?
    Contact U.S. Geological Survey for details.

Who wrote the metadata?

Dates:
Last modified: 01-Feb-2017
Metadata author:
Xan Fredericks
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL
Cartographer/Lidar Coordinator
600 4th Street South
St. Petersburg, FL
USA

727 502-8086 (voice)
afredericks@usgs.gov
Hours_of_Service: M-F, 8:00-4:00 ET
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

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