2014 Horry County, South Carolina Lidar

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This graphic shows the lidar footprint for the 2014 Horry County, South Carolina lidar project.

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This data set is the project specified flightline vector data. | Type of Source Media: Vector dataset

This data set is the project specified hydrologic breakline deliverable. | Type of Source Media: 3-d breakline dataset

This data set is the project specified acquired point cloud data. | Type of Source Media: Lidar dataset

This data set is the project specified acquired point cloud data. | Type of Source Media: Lidar dataset

This data set is the project specified lidar deliverables. | Type of Source Media: Lidar dataset

This data set is the project specified acquired ground control and QAQC control data. | Type of Source Media: Control dataset

This data set is the project specified tile index and data extent. | Type of Source Media: vector dataset

Using one Leica ALS70 (lidar) system on board a Cessna 404 Titan fixed-wing aircraft, lidar data, at a nominal pulse spacing (NPS) of 0.7 meters, was collected for this task order (approximately 1092 square miles). AGL = 6500 feet - Aircraft Speed = 150 Knots, Field of View (Full) = 40 degrees, Pulse Rate = 272.0 kHz, Scan Rate = 42.3 Hz, with an average side lap of 28.7%. Multiple returns were recorded for each laser pulse along with an intensity value for each return. Five (5) missions were flown between February 22, 2014 and February 25, 2014. One (1) Global Navigation Satellite System (GNSS) Base Station was used in support of the lidar data acquisition. Specific information regarding latitude, longitude, and ellipsoid height to the L1 phase center is included in the lidar processing report. Multiple returns were recorded for each laser pulse along with an intensity value for each return. The lidar data acquisition parameters for this mission are detailed in the lidar processing report for this task order. For all acquired lidar data as part of entire Horry County Elevation Data and Imagery task order, the geoid used to reduce satellite derived elevations to orthometric heights was GEOID12A. Data for the task order is referenced to the StatePlane Zone of South Carolina, North American Datum of 1983 (2011) International Feet, and NAVD88, in International Feet. Once the data acquisition and GPS processing phases are complete, the lidar data was processed immediately to verify the coverage had no voids. The GPS and IMU data was post processed using differential and Kalman filter algorithms to derive a best estimate of trajectory. The quality of the solution was verified to be consistent with the accuracy requirements of the project. The SBET was used to reduce the lidar slant range measurements to a raw reflective surface for each flight line. The coverage was classified to extract a bare earth digital elevation model (DEM) and separate last returns. The ALS70 calibration and system performance is verified on a periodic basis using Woolpert's calibration range. The calibration range consists of a large building and runway. The edges of the building and control points along the runway have been located using conventional survey methods. Inertial measurement unit (IMU) misalignment angles and horizontal accuracy are calculated by comparing the position of the building edges between opposing flight lines. The scanner scale factor and vertical accuracy is calculated through comparison of lidar data against control points along the runway. Field calibration is performed on all flight lines to refine the IMU misalignment angles. IMU misalignment angles are calculated from the relative displacement of features within the overlap region of adjacent (and opposing) flight lines. The raw lidar data is reduced using the refined misalignment angles.

Using one Leica ALS50 (lidar) system on board a Cessna 208B fixed-wing aircraft, lidar data, at a nominal pulse spacing (NPS) of 0.3 meters, was collected for the coastal portion of the Horry County AOI. AGL = 1968 feet - Aircraft Speed = 110 Knots, Field of View (Full) = 40 degrees, Pulse Rate = 130.0 kHz, Scan Rate = 42.9 Hz, with an average side lap of 50%. Multiple returns were recorded for each laser pulse along with an intensity value for each return. The collection occurred on two dates: January 22, 2014 and January 26, 2014. The absolute accuracy of the coastal data set was tested by Quantum Geospatial prior to delivery to Woolpert for inclusion to the overall Horry County dataset yielding a result of 2.9 cm RMSEz. The coastal data set was assessed for data coverage, GPS and IMU quality, collection density, and calibration quality by Woolpert prior to merging with the Woolpert collected data for the remainder of the county. Final project accuracy statistical analysis was performed on the merged county and coastal dataset. For all acquired lidar data as part of entire Horry County Elevation Data and Imagery task order, the geoid used to reduce satellite derived elevations to orthometric heights was GEOID12A. Data for the task order is referenced to the State Plane Zone of South Carolina, North American Datum of 1983 (2011) International Feet, and NAVD88, in International Feet. Once the data acquisition and GPS processing phases are complete, the lidar data was processed immediately to verify the coverage had no voids. The GPS and IMU data was post processed using differential and Kalman filter algorithms to derive a best estimate of trajectory. The quality of the solution was verified to be consistent with the accuracy requirements of the project. The SBET was used to reduce the lidar slant range measurements to a raw reflective surface for each flight line. The coverage was classified to extract a bare earth digital elevation model (DEM) and separate last returns.

Ground control and QAQC control point survey was performed by Woolpert surveyors, to support the NOAA Horry County Elevation Data and Imagery project. All surveys were performed in such a way as to achieve ground control that supports lidar data at 9.25 cm RMSE accuracy and satisfy a local network accuracy of 5 cm at a 95% confidence level. All ground control survey field activities took place from 03/18/2014 through 03/22/14. Woolpert collected control data for data processing as supplemental QAQC points. The supplemental QAQC points were collected to be used in independent accuracy testing. The survey was performed using one (1) Trimble Navigation R8 Model 3 GNSS dual frequency GPS receiver with Air Link Communications Raven CDMA cellular modem, one (1) Trimble Navigation R8 Model 2 receiver, one (1) Trimble Navigation R8 receiver, and one (1) Trimble Navigation R8 Model 3 GNSS dual frequency GPS receiver with Air Link Communications Raven CDMA cellular modem as a rover. Woolpert surveyors,utilizing Real-Time Kinematic GPS techniques, made observations on 27 ground control points and 21 quality control check points using 1-second epoch rates and observations of 60 to 180 seconds. Each station was occupied twice to insure necessary horizontal and vertical accuracies. All GPS ground control observations were processed using Trimble Navigation's Trimble Business Center. All horizontal GPS control was based on South Carolina State Plane Zone (3900), NAD83(2011) expressed in International Feet. The vertical datum used for this project was based on the North American Vertical Datum of 1988 (NAVD88), GEOID12A, also expressed in International Feet.

The individual flight lines were inspected to ensure the systematic and residual errors have been identified and removed. Then, the flight lines were compared to adjacent flight lines for any mismatches to obtain a homogeneous coverage throughout the project area. The point cloud underwent a classification process to determine bare-earth points and non-ground points utilizing "first and only" as well as "last of many" lidar returns. This process determined Default (Class 1), Ground (Class 2), Noise (Class 7), Water (Class 9), Ignored Ground (Class 10), Overlap Default (Class 17) and Overlap Ground (Class 18). The bare-earth (Class 2 - Ground) lidar points underwent a manual QA/QC step to verify the quality of the DEM as well as a peer-based QC review. This included a review of the DEM surface to remove artifacts and ensure topographic quality. Classification of water (class 9) and ignored ground (class 10) was completed via the use of the hydrologic breaklines collected for the hydro-flattening phase. The overlap classes were determined by first identifying the overlapping areas and reclassifying the LAS data by offset from a corridor. This allows the returns located on the edge of the swath to be removed from the bare earth coverage in an effort to produce a more uniform data density. The returns determined to be overlap are then further classified to produce overlap default (class 17) and overlap ground (class 18). The surveyed ground control points are used to make vertical adjustments to the data set and to perform the accuracy checks and statistical analysis of the lidar dataset. Supervisory QC monitoring of work in progress and completed editing ensured consistency of classification character and adherence to project requirements across the entire project area. The resulting deliverables for this task order consist of classified LAS file in LAS 1.2 format, 4 feet pixel size DEM files in ERDAS IMG format, and Hydrologic Breakline, Flightline Vector, and Control Point data in ESRI Geodatabase format.

The individual flight lines were inspected to ensure the systematic and residual errors have been identified and removed. Then, the flight lines were compared to adjacent flight lines for any mismatches to obtain a homogeneous coverage throughout the project area. The point cloud underwent a classification process to determine bare-earth points and non-ground points utilizing "first and only" as well as "last of many" lidar returns. This process determined Default (Class 1), Ground (Class 2), Noise (Class 7), Water (Class 9), Ignored Ground (Class 10), Overlap Default (Class 17) and Overlap Ground (Class 18). The bare-earth (Class 2 - Ground) lidar points underwent a manual QA/QC step to verify the quality of the DEM as well as a peer-based QC review. This included a review of the DEM surface to remove artifacts and ensure topographic quality. Classification of water (class 9) and ignored ground (class 10) was completed via the use of the hydrologic breaklines collected for the hydro-flattening phase. The overlap classes were determined by first identifying the overlapping areas and reclassifying the LAS data by offset from a corridor. This allows the returns located on the edge of the swath to be removed from the bare earth coverage in an effort to produce a more uniform data density. The returns determined to be overlap are then further classified to produce overlap default (class 17) and overlap ground (class 18). The surveyed ground control points are used to make vertical adjustments to the data set and to perform the accuracy checks and statistical analysis of the lidar dataset. Supervisory QC monitoring of work in progress and completed editing ensured consistency of classification character and adherence to project requirements across the entire project area. The hydrologic breaklines were produced according to USGSv1.0 specifications. The compilation procedure included use of lidar intensity, bare earth surface model, point cloud data, open source imagery in an effort to manually compile hydrologic features in a 2-d environment. Following the compilation phase, a separate process was used to adjust the breakline data to best match the water level at the time of the lidar collection. Any ponds and/or lakes were adjusted to be at or just below the bank and to be at a constant elevation. Any streams were adjusted to be at or just below the bank and to be monotonic. Manual QAQC and peer-based QC review was performed on all delineated data to ensure horizontal placement quality and on all adjusted data to ensure vertical placement quality. The final hydrologic breakline product was delivered in ESRI Geodatabase format and was also used in the processing of the DEM deliverable. The resulting deliverables for this task order consist of classified LAS file in LAS 1.2 format, 4 feet pixel size DEM files in ERDAS IMG format, and Hydrologic Breakline, Flightline Vector, and Control Point data in ESRI Geodatabase format.

Tile Size: 5,000ft x 5,000ft. The tile file name was derived from the southwest corner of each tile. Project data extent was provided by NOAA and subsequently buffered by 1 kilometer and provided in shape file format. Project deliverables were clipped to the 1 kilometer data extent.

The flightline vectors were generated by importing the Raw LAS strips into Geocue software. Bounding polygons are created around each individual swath. The polygons were exported to shapefile and a centerline was generated for each. Attribution was added to each flightline in the form of line number, date of acquisition, and start/stop times.

The NOAA Office for Coastal Management (OCM) received 1488 files in las format from Woolpert. The files contained lidar elevation and intensity measurements. The data were in State Plane South Carolina FIPS 3900 NAD 1983 (2011) Intl Ft coordinates and North American Vertical Datum of 1988 (GEOID12A) Intl Ft heights. OCM performed the following processing for data storage and Digital Coast provisioning purposes: 1. LAS files were compressed to laz format using laszip. 2. Data were checked for elevation outliers and points with elevation values less than -5 feet and greater than 700 feet were dropped from the data set. 3. Data were converted from State Plane South Carolina FIPS 3900 NAD83(2011) coordinates to geographic coordinates 4. Data were converted from International feet elevations to meters. 5. The data were converted from North American Vertical Datum of 1988(GEOID12A) heights to ellipsoid heights using GEOID12A.