2009 SCDNR Horry County Lidar

Sanborn Map Company completed the original classification of the multiple return LiDAR of Horry County, South Carolina in 2009. In 2013, Dewberry was tasked with reviewing and updating the original LiDAR product. The nominal point spacing for this project is 1.4 meters. Dewberry used proprietary procedures to update and reclassify the LAS according to updated project specifications: 1-Unclassified, 2-Ground, 7-Noise,8- Model Key Points, 9-Water, 10-Ignored Ground, 13- Points removed from bridges and culverts (class 13 were converted to class 15 to fit the OCM scheme)

The purpose of this LiDAR data was to produce high accuracy 3D elevation products, including tiled LiDAR in LAS 1.2 format, 3D breaklines, and ESRI grid raster format 10 ft cell size hydro flattened Digital Elevation Models (DEMs).

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A footprint of this data set may be viewed in Google Earth at: https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/3656/supplemental/sc2009_scdnr_horry_m3656.kmz . A report of the processing steps can be found here: https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/3656/supplemental/sc2009_scdnr_horry_lidarreport_m3656.pdf

As needed - Dewberry 2013-2014 (reprocessed, did not recollect data)

LiDAR points in LAS 1.2 format

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

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=3656

The data set is dynamically generated based on user-specified parameters.;

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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be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions.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. These data depict the heights at the time of the survey and are only accurate for that time.

Lidar source compiled to meet 1 meter horizontal accuracy.; Quantitative Value: 1.0 meters, Test that produced the value: Dewberry does not perform independent horizontal accuracy testing on the LiDAR. LiDAR vendors perform calibrations on the LiDAR sensor and compare data to adjoining flight lines to ensure LiDAR meets the 1 meter horizontal accuracy standard at the 95% confidence level.

The vertical accuracy of the original LiDAR was tested by Dewberry in 2012 (or whenever we performed the original QAQC). Vertical Accuracy was not re-tested post updates performed in 2014.

The vertical accuracy of the of the full LiDAR project was tested by Dewberry with independent survey checkpoints. The survey checkpoints were evenly distributed throughout the project area and are located in areas of bare earth and open terrain, high grass, pavement, brush and low trees, and forest. The vertical accuracy is tested by comparing survey checkpoints to a triangulated irregular network (TIN) that is created from the LiDAR ground points. Checkpoints are always compared to interpolated surfaces created from the LiDAR point cloud because it is unlikely that a survey checkpoint will be located at the location of a discrete LiDAR point.

Checkpoints in open terrain were used to compute the Fundamental Vertical Accuracy (FVA). Project specifications required a FVA of 0.80 ft (24.5 cm) based on a RMSEz (0.41 ft/12.5 cm) x 1.9600. All checkpoints were used to compute the Consolidated Vertical Accuracy (CVA). Project specifications required a CVA of 1.19 ft (36.3 cm) based on the 95th percentile.; Quantitative Value: 0.183 meters, Test that produced the value: 0.6 ft (18.3cm) Based on the vertical accuracy testing conducted by Dewberry, using NSSDA and FEMA methodology, vertical accuracy at the 95% confidence level (called Accuracyz) is computed by the formula RMSEz x 1.9600. The dataset for Horry County, South Carolina satisfies the criteria:

Lidar dataset tested 0.32 ft vertical accuracy at 95% confidence level in open terrain, based on RMSEz (0.33 ft) x 1.9600.

A visual qualitative assessment was performed to ensure data completeness and bare earth data cleanliness. No void or missing data and data passes vertical accuracy specifications.

Data covers the tile scheme provided for the project area.