2013-2014 U.S. Geological Survey CMGP LiDAR: Post Sandy (MA, NH, RI)

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This graphic shows the lidar coverage for the 2013 and 2014 lidar acquisition for MA, NH and RI.

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Using two Leica ALS70 (lidar) systems on board a Cessna 404 and Cessna 310 aircraft, lidar data, at a nominal pulse spacing (NPS) of 0.7 meters, was collected for this task order (approximately 304 square miles). AGL = 7500 feet - Aircraft Speed = 150 Knots, Field of View (Full) = 32 degrees, Pulse Rate = 239 kHz, Scan Rate = 41.6 Hz, with an average side lap of 25%. Multiple returns were recorded for each laser pulse along with an intensity value for each return. This acquisition was part of a larger effort designed to capture one other USGS task order AOI in New Jersey. For the New York portion of the collection, ten (10) missions were flown between March 21, 2014 and April 21, 2014. Six (6) Global Navigation Satellite System (GNSS) Base Stations were 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. As a supplement to the USGS task order collection, Woolpert acquired lidar data of New York City as part of a 2013 task order for the NGA. This was acquired using a Leica ALS70 (lidar) system on board a Cessna 404 and produced lidar data, at a nominal pulse spacing (NPS) of 0.91 meters. AGL = 7500 feet - Aircraft Speed = 150 Knots, Field of View (Full) = 40 degrees, Pulse Rate = 239 kHz, Scan Rate = 36.9 Hz, with an average side lap of 30%. For the NGA task order portion of the collection One (1) mission was used. This mission was flown on August 6, 2013. 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 flight plan for the New York City NGA Lidar task order was developed with 11 additional cross flights over the Manhattan Metropolitan area to minimize data shadowing and data voids in the lidar dataset caused by tall buildings.

USGS requested use of this data from the NGA in order to reduce the duplication of lidar data acquisition effort on the New York CMGP Sandy Lidar task order. The NGA approved the use of this lidar data for the USGS task order. Following the approval by NGA, Woolpert was able to utilize the cross flights acquired as part of the NGA task order to minimize data shadowing and data voids caused by tall buildings in the USGS New York CMGP Sandy Lidar task order AOI. 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 USGS New York City task order, the geoid used to reduce satellite derived elevations to orthometric heights was GEOID12A. Data for the task order is referenced to the UTM Zone 18N, North American Datum of 1983 (2011), and NAVD88, in meters. 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.

Ground control and QAQC control point survey was performed by Woolpert surveyors, to support the USGS New York CMGP Sandy Lidar 0.7 Meter NPS LIDAR 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 12/03/2013 thru 05/07/14. 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 two (2) Trimble Navigation R8 Model 3 GNSS Dual Frequency GPS receivers with a Trimble TDL-450 radio as dual base stations in conjunction with simultaneous data collected across two (2) Continuously Operating Reference Stations (CORS) GPS receivers. Additionally, Woolpert utilized a Trimble Navigation R8 Model 3 GNSS dual-frequency GPS receiver and a TSC2 data collector as a rover. Woolpert surveyors,utilizing Real-Time Kinematic GPS techniques, made observations 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 UTM Zone 18N, NAD83(2011) expressed in meters. The vertical datum used for this project was based on the North American Vertical Datum of 1988 (NAVD88), GEOID12A, also expressed in meters.

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 homogenous 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, Raw Swath LAS files in LAS 1.2 format, 1 meter pixel size DEM files in ERDAS IMG format, 1 meter pixel size 8-bit Intensity files in GeoTIFF format, and Hydrologic Breakline data in ESRI shape file 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 homogenous 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 incuded 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 seperate 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 shape file format and was also used in the processing of the DEM deliverable.

Tile Size: 1,500m x 1,500m. The tile file name was derived from the southwest corner of each tile. The tiles are named based on the US National Grid. Project data extent was provided by USGS and subsequently buffered by 100 meters and provided in shape file format. Project deliverables were clipped to the 100 meter data extent.

The NOAA Office for Coastal Management (OCM) received the topographic files in classified LAS format from USGS with V1 specifications. The data were received in UTM Zone 18N and 19N NAD83 coordinates (meters) and vertically referenced to NAVD88 using the Geoid12a model in meters. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. LAS files were compressed to LAZ format with LASTools.

2. LAS files were removed of an duplicated points and extraneous points were reclassified to noise.

3. Zone 19 was processed with little changes though Zone 18 were transformed to Zone 19 and checks run to remove all duplicated points which may have been delivered in both Zone 18 and 19. There 93 tiles effecting, of which 20 were completely removed since all the points already existed in the Zone 19 delivery.

4. The LAS files were transformed to geographic (decimal degrees), ellipsoidal coordinates (meters) referenced to the Geoid12a model.