MD/PA Sandy Supplemental Lidar - Classified LAS 1.2

Collected at a nominal pulse spacing (NPS) of 0.7 meters.

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This graphic displays the footprint for this lidar data set.

Origination location of the data.

Original metadata indicates a project report exists. This was not found on the Maryland iMAP site and we currently don't have it.

This data set is the project specified acquired point cloud data.

This data set is the project specified lidar deliverables.

This data set is the project specified acquired ground control and QAQC control data.

Using two Leica ALS70 (lidar) systems on board a Cessna 310 and Cessna 404 aircraft respectively, high density data, at a nominal pulse spacing (NPS) of 0.7 meters, were collected for this task order (approximately 1,813 square miles). Leica Specs -

For Kent & Talbot (MD):

AGL = 1,981 meters - Aircraft Speed = 150 Knots, Field of View (Full) = 40 degrees, Pulse Rate = 272 kHz, Scan Rate = 41.5 Hz, with an average side lap of 25%. Multiple returns were recorded for each laser pulse along with an intensity value for each return.

For Carroll & Baltimore (MD), Chester (PA):

AGL = 2,286 meters - Aircraft Speed = 150 Knots, Field of View (Full) = 32 degrees, Pulse Rate = 239 kHz, Scan Rate = 40 Hz, with an average side lap of 25%. Multiple returns were recorded for each laser pulse along with an intensity value for each return.Seventeen (17) missions were flown between December 7, 2014 and January 2, 2015. Five (5) 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. 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.

The field crews utilized VRS RTK GPS by logging into the KeyNet RTK GPS Network to obtain real

time corrections of the collected GPS data. This is a technique used in land surveying based on the use of

carrier phase measurements of the GPS and GLONASS signals where a network calculated reference

station provides the real-time corrections, providing up to centimeter-level accuracy. This methodology

allowed for efficient survey grade observations for sensor calibrations and ground-truthing. Woolpert

Woolpert, Inc. Sandy Supplemental

March 2015 MD / PA QL2 Lidar

USGS/NGTOC Section 1: Page 3 of 3

utilized a single Trimble Navigation R8 dual-frequency geodetic GPS receiver at the rover end of the

vector for this task. The survey was conducted using a 1-second epoch rate, in a fixed solution RTK

mode with each GPS session lasting 120 epochs to 180 epochs

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 including overlap default, ground, water, and ignored ground are then applied an overlap flag and reclassified to their respective standard classification value.. 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.

Point cloud data were downloaded from Maryland iMAP in LAZ format, UTM 18, NAVD88 (Geoid12a) meters in October 2017. Data were reprojected to geographic coordinates and reduced to ellipsoid heights. Data were then ingested into the Digital Coast Data Access Viewer.