2016 USGS Lidar DEM: Assateague Island, Maryland and Virginia, Post-Hurricane Hermine, 10-12 September 2016

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.

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

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.

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.

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the Office for Coastal Management or its partners

Data is available online for custom downloads

None

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

Microsoft Windows 7 Enterprise Service Pack 1; Esri ArcCatalog 10.2.2.3552

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.Qualitative value:0.072 meters AccuracyZ at the 95 percent Confidence Interval for Raw LAS NVA. 0.063 meters AccuracyZ at the 95 percent Confidence Interval for DEM NVA. 0.137 meters AccuracyZ at the 95th percentile for DEM VVA., Test that produced the value: Quantum Spatial reports that the 13 independent NVA check points were surveyed using the closed level loop technique. Elevations interpolated from the unclassified lidar surface were compared to the elevation values of the surveyed NVA check points. The RMSE was computed to be 0.037 meters resulting in an AccuracyZ at the 95% confidence level of 0.072 meters. The 13 NVA check points were also compared to the elevations of the derived bare earth DEMs. The RMSE was computed to be 0.032 meters resulting in an AccuracyZ of 0.063 meters at the 95% confidence level. NVA AccuracyZ has been tested and meets the required 19.6 meter NVA at 95% confidence level using (RMSEz * 1.9600) for both the raw lidar point cloud and derived DEMs, as defined by the National Standards for Spatial Data Accuracy (NSSDA) and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines. The 13 VVA check points were also surveyed using the closed level loop technique. Elevations for these points were compared to the elevations of the derived bare earth DEMs. The RMSE was computed to be 0.078 meters resulting in an AccuracyZ of 0.137 meters at the 95th percentile. AccuracyZ has been tested on the derived bare earth DEMs and meets the required 29.4 meter VVA using the 95th percentile of the absolute value of all vertical errors in all combined vegetation classes as defined by the National Standards for Spatial Data Accuracy (NSSDA); and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines.

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.

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.

Quantum Spatial acquired and processed topobathy lidar data to DEMs. USGS combined the individual DEM tiles into a single GeoTiff. NOAA updated the georeferencing information and created a cloud optimized GeoTiff.