2012 South Carolina DNR Lidar: McCormick County

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This graphic shows the lidar coverage for the 2012 lidar project covering McCormick County, South Carolina.

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using 'fgdc_to_inport_xml.pl' script. Contact Tyler Christensen (NOS) for details.

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Towill Inc. employed an Optech Orion M-200 Lidar system in the acquisition of this Lidar data. The planned acquisition parameters were as follows:

Target altitude - 1500 meters AMT; System PRF - 70kHz; Scan Half Angle - 20 degrees; Scan Rate - 38 hertz; Aircraft Speed - 150 knots; Target sidelap - 50 percent.

All missions originated and/or terminated at the Rock Hill Airport. A GPS base station was operating at the airport during every lift. The South Carolina Geodetic Survey, was contacted prior to the start of the Lidar acquisition to arrange for 1 Hertz data logging of several of the active CORS stations included in the primary survey network. The data from these stations were downloaded and applied in the post-processing of the kinematic Airborne GPS (AGPS) data.

Airborne GPS and Inertial Measurement Unit (IMU) data were acquired by the Applanix POS Inertial Navigation System during the missions. The post-processed POS data results in a 200 Hertz, 6-parameter aircraft trajectory (x, y, z, roll, pitch, yaw).

The AGPS and IMU data were processed immediately following each mission. In addition, a sample of the Lidar data was post-processed at the completion of the missions and the data were reviewed to ensure correct system operation and data coverage.

The kinematic AGPS data were post-processed using Novatel, Inc.'s Grafnav version 8.20 software, the de facto kinematic GPS post-processing package in the airborne remote sensing industry.

The post-processed AGPS trajectory is combined with the raw 200 Hertz IMU observations in a loosely-coupled Kalman filter-based processing algorithm to produce the final high-frequency Smoothed Best Estimated Trajectory (SBET). Applanix's POSPac software, version 4.4, is employed in this process.

Final Lidar data processing is accomplished using Optech's DASHMap software, version 5.01.

Dewberry utilizes a variety of software suites for inventory management, classification, and data processing. All LiDAR related processes begin by importing the data into the GeoCue task management software. GeoCue allows the data to retain its delivered tiling scheme (5000 ft by 5000 ft). The tiled data is then opened in Terrascan where Dewberry uses proprietary ground classification routines to remove any non-ground points and generate an accurate ground surface. The ground routine consists of three main parameters (building size, iteration angle, and iteration distance); by adjusting these parameters and running several iterations of this routine an initial ground surface is developed. The building size parameter sets a roaming window size. Each tile is loaded with neighboring points from adjacent tiles and the routine classifies the data section by section based on this roaming window size. The second most important parameter is the maximum terrain angle, which sets the highest allowed terrain angle within the model. Once the ground routine has been completed a manual quality control routine is done using hillshades, cross-sections, and profiles within the Terrasolid software suite. After this QC step, a peer review and supervisor manual inspection is completed on a percentage of the classified tiles based on the project size and variability of the terrain. After the ground classification corrections were completed, the dataset was processed through a water classification routine that utilizes breaklines compiled by Dewberry to automatically classify hydrographic features. The water classification routine selects ground points within the breakline polygons and automatically classifies them as class 9, water. During this water classification routine, points which are in close proximity (1 m) to the hydrographic features are moved to class 10, an ignored ground. In addition to classes 1, 2, 8, 9, and 10, the project allows for a Class 7, noise points. This class was only used if needed when points could manually be identified as low/high points.

The fully classified dataset is then processed through Dewberry's comprehensive quality control program.

The data was classified as follows:

Class 1 = Unclassified. This class includes vegetation, buildings, noise etc.

Class 2 = Ground

Class 7 = Noise

Class 8 = Model Key Points

Class 9 = Water

Class 10 = Ignored Ground

Class 11 = Withheld

Class 13 = Points Removed from Bridges

The LAS header information was verified to contain the following:

Class (Integer)

GPS Week Time (0.0001 seconds)

Easting (0.001 m)

Northing (0.001 m)

Elevation (0.001 m)

Echo Number (Integer 1 to 4)

Echo (Integer 1 to 4)

Intensity (8 bit integer)

Flight Line (Integer)

Scan Angle (Integer degree)

The NOAA Office for Coastal Management (OCM) received the files in LAS format from the South Carolina Department of Natural Resources (SC DNR) via a hard-drive device (HDD). The drive contained a number of South Carolina counties from a number of acquisition years. The files contained lidar elevation and intensity measurements. The data were in State Plane Zone 3900 in feet and NAVD88 (orthometric) vertical coordinates in feet. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The LAS files were compressed to LAZ files while also transforming the horizontal projection from State Plane coordinates in feet to geographic coordinates decimal degrees.

2. The LAZ files' vertical datum was converted from NAVD88 in feet (orthometric) to GRS80 (ellipsoid) heights in meters using Geoid 09.

3. The data were sorted by time and duplicates removed, updating the headers.