Coastal Topography—Assateague Island, Maryland and Virginia, Post-Hurricane Joaquin, 26 November 2015
Binary point-cloud data were produced for Assateague Island, Maryland and Virginia, post-Hurricane Joaquin, from remotely sensed, geographically referenced elevation measurements collected by Quantum Spatial using a Leica ALS70 (1064-nm wavelength) lidar sensor.
Processed data products are used by the U.S. Geological Survey (USGS) 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.
U.S. Geological Survey, 20160506, Coastal Topography—Assateague Island, Maryland and Virginia, Post-Hurricane Joaquin, 26 November 2015: U.S. Geological Survey Data Release doi:10.5066/F70P0X4G, U.S. Geological Survey, St. Petersburg, FL.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.01
Ordinates (y-coordinates) are specified to the nearest 0.01
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 6378137.000000.
The flattening of the ellipsoid used is 1/298.25722210100002.
Altitude_Datum_Name:North American Vertical Datum of 1988 (GEOID12B) Altitude_Resolution:0.15 Altitude_Distance_Units:meters Altitude_Encoding_Method:
Explicit elevation coordinate included with horizontal coordinates
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.
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), 2015-344-FA. Additional survey and data details are available at http://cmgds.marine.usgs.gov/fan_info.php?fan=2015-344-FA. USGS Contract: G10PC00026 Task Order Number: G16PD00038
Classified LAS Creation: The bare-earth surface is then manually reviewed to ensure correct classification on the Class 2 (Ground) points. After the bare-earth surface is finalized, it is then used to generate all hydro-breaklines through heads-up digitization. All ground (ASPRS Class 2) LiDAR data inside of the lake/pond and double-line drain hydro-flattening breaklines were then classified to water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 1 meter was also used around each hydro-flattened feature to classify these ground (ASPRS Class 2) points to ignored ground (ASPRS Class 10). All lake/pond island and double-line drain island features were checked to ensure that the ground (ASPRS Class 2) points were reclassified to the correct classification after the automated classification was completed. All bridge decks were classified to Class 17. All overlap data were processed through automated functionality provided by TerraScan to classify the overlapping flight line data to approved classes by USGS. The overlap data were identified using the Overlap Flag, per LAS 1.4 specifications. All data were manually reviewed and any remaining artifacts removed using functionality provided by TerraScan and TerraModeler. Global Mapper was used as a final check of the bare-earth dataset. GeoCue was then used to create the deliverable industry-standard LAS files for both the unclassified point-cloud data and the bare-earth data. Quantum Spatial proprietary software was used to perform final statistical analysis of the classes in the LAS files, on a per-tile level to verify final classification metrics and full LAS header information.
Person who carried out this activity:
523 Wellington Way
Hours_of_Service:Monday through Friday 8:00 AM to 5:00 PM (Eastern Time)
Data sources produced in this process:
Date: 04-Jan-2017 (process 2 of 2)
Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.
Person who carried out this activity:
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 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.
Where are the gaps in the data? What is missing?
Quantum Spatial reports that these raw LAS data files include all data points collected and that no points have been removed or excluded. Quantum Spatial performed a visual qualitative assessment to ensure data completeness and reported no void areas or missing data exist. Quantum Spatial reports that the raw point cloud is of good quality and data passes Nonvegetated Vertical Accuracy specifications.
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.
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.