2013 South Carolina DNR Lidar: Greenville County

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This graphic shows the lidar coverage for the 2013 lidar project covering Greenville County, South Carolina.

Date that the source FGDC record was last modified.

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Data for the South Carolina Dept of Natural Resources project was acquired by The Atlantic Group. The Atlantic Group provided high accuracy, calibrated multiple return LiDAR for roughly 1,510 square miles around Greenville County, SC and Spartanburg County, SC. The data was delivered in the South Carolina State Plane (International Feet) coordinate system, horizontal datum NAD83 (NSRS 2007), vertical datum NAVD88, Geoid 09, Feet. Atlantic Group operated the collection aircraft; a Cessna T-210 (Tail # N732JE) outfitted with a LEICA ALS70-HP LiDAR system from Atlantic Group's facilities in Courtland. The LiDAR was completed over twenty lifts.

LIDAR acquisition began on February 21, 2013 (julian day 052) and was completed on March 17, 2013 (julian day 076). Two hundred and twenty-six (226) passes were planned for Greenville and Spartanburg Counties in South Carolina as a series of parallel flight lines with cross flight lines for the purposes of quality control. The flight plan included a zigzag flight line collection as a result of the inherent IMU drift associated with all IMU systems. In order to reduce any margin for error in the flight plan, Atlantic Group followed FEMA's Appendix A "guidelines" for flight planning and, at a minimum, includes the following criteria: A digital flight line layout using LEICA MISSION PRO flight design software for direct integration into the aircraft flight navigation system; planned flight lines, flight line numbers, and coverage area; LiDAR coverage extended by a predetermined margin beyond all project borders to ensure necessary over-edge coverage appropriate for specific task order deliverables; and local restrictions related to air space and any controlled areas have been investigated so that required permissions can be obtained in a timely manner with respect to schedule. Additionally, Atlantic Group will file our flight plans as required by local Air Traffic Control (ATC) prior to each mission.

Atlantic Group monitored weather and atmospheric conditions and conducted LiDAR missions only when no conditions exist below the sensor that will affect the collection of data. These conditions include leaf-off for hardwoods, no snow, rain, fog, smoke, mist and low clouds. LiDAR systems are active sensors, not requiring light, thus missions may be conducted during night hours when weather restrictions do not prevent collection. Atlantic Group accesses reliable weather sites and indicators (webcams) to establish the highest probability for successful collection in order to position our sensor to maximize successful data acquisition.

Within 72-hours prior to the planned day(s) of acquisition, Atlantic Group closely monitored the weather, checking all sources for forecasts at least twice daily. As soon as weather conditions were conducive to acquisition, our aircraft mobilized to the project site to begin data collection. Once on site, the acquisition team took responsibility for weather analysis. Upon notification to proceed, the flight crew loaded the flight plans and validated the flight parameters. The Acquisition Manager contacted air traffic control and coordinated flight pattern requirements. LiDAR acquisition began immediately upon notification that control base stations were in place. During flight operations, the flight crew monitored weather and atmospheric conditions. LiDAR missions were flown only when no condition existed below the sensor that would affect the collection of data. The pilot constantly monitored the aircraft course, position, pitch, roll, and yaw of the aircraft. The sensor operator monitored the sensor, the status of PDOPs, and performed the first Q/C review during acquisition. The flight crew constantly reviewed weather and cloud locations. Any flight lines impacted by unfavorable conditions were marked as invalid and re-flown immediately or at an optimal time. Data was checked after each mission and after all flown missions to verify complete coverage.

Atlantic Group LiDAR sensors are calibrated at a designated site located at the Lawrence County Airport in Courtland, Alabama and are periodically checked and adjusted to minimize corrections at project sites. All surveys were performed to Federal Geodetic Control Subcommittee (FGCS) guidelines. Atlantic Group maximized existing NGS control and the ALDOT CORS stations to provide the control network, designed with proper redundancies, session occupation times, and time between sessions according to the applicable NOS technical standards. GPS observations were conducted using Federal Geodetic Control Committee (FGCC) approved dual frequency GPS receivers. A minimum of two fixed-height tripods were used as ground base stations running at a one (1.0) second epoch collection rate during every mission, typically at a minimum of four hours. The control locations are planned to ensure a 28km baseline distance from the furthest flight line distance. Also, the KP index is considered prior to mission collection and no collection occurred when the KP index was at or above 4.

Atlantic Group utilized a combination of software tools to calibrate each flight line to each other as well as to control points. LEICA ALS post processing software was used to extract each individual flight line with initial settings for heading, roll, pitch, and scale. Once these lines are extracted they're then imported into Terra Scan to find the final heading, roll, pitch, and scale adjustments. Distance measurements are taken from flight line to flight line as well as known or established control points. These measurements are then applied to the flight lines through the terra scan software. The lines are then extracted with the calibration corrections and imported into the GeoCue software for classification. Utilizing GeoCue LiDAR ortho raster checklist, final calibration QC is performed to verify relative accuracy of less than or equal to 7cm RMSE(z) within individual swaths. Upon completion of QC the final LAS swaths are exported through Terra Scan based on client parameters and specifications.

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. The swath data is tiled according to project specifications (5000 ft x 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. Before the actual ground routine is run points with scan angles greater than plus or minus 20 degrees are classified to class 11, withheld. Due to these higher scan angles these points have the potential to introduce issues into the ground and are therefore not used in the final 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 that are within 1 foot of the hydrographic features are moved to class 10, an ignored ground due to breakline proximity.

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

Class 11 = Withheld Points

Class 13 = Bridges and Culverts

The LAS header information was verified to contain the following:

Class (Integer)

Adjusted GPS Time (0.000001 seconds)

Easting (0.001 ft)

Northing (0.001 ft)

Elevation (0.001 ft)

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 LAZ format from the South Carolina Department of Natural Resources (SCDNR) via a HDD. The files contained lidar elevation and intensity measurements. The data were in State Plane Zone 3900, NAVD88 (orthometric) heights in meters. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The data were converted from State Plane coordinates to geographic coordinates.

2. The data were converted from NAVD88 (orthometric) heights in meters to GRS80 (ellipsoid) heights in meters using Geoid 09.

3. The project files were reclassified to fit the OCM scheme: classes 11 and 13 were reclassified to 15 and 17

4. Erroneous elevations were removed.