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The LiDAR survey occurred between July 31, 2015 and October 15, 1015 utilizing a Leica ALS80 mounted in a Cessna Grand Caravan. The systems
were programmed to emit single pulses at around 369 kHz and flown at 1,500 m AGL, capturing a scan angle of 15 degrees from nadir. These
settings were developed to yield points with an average native density of greater than eight pulses per square meter over terrestrial surfaces.
To solve for laser point position, an accurate description of aircraft position and attitude is vital. Aircraft position is described as x, y, and z and was
measured twice per second (two hertz) by an onboard differential GPS unit. Aircraft attitude is described as pitch, roll, and yaw (heading) and was
measured 200 times per second (200 hertz) from an onboard inertial measurement unit (IMU).
The LiDAR sensor operators constantly monitored the data collection settings during
acquisition of the data, including pulse rate, power setting, scan rate, gain, field of view,
and pulse mode. For each flight, the crew performed airborne calibration maneuvers
designed to improve the calibration results during the data processing stage. They
were also in constant communication with the ground crew to ensure proper ground
GPS coverage for data quality. The LiDAR coverage was completed with no data gaps
or voids, barring non-reflective surfaces (e.g., open water, wet asphalt). All necessary
measures were taken to acquire data under good conditions (e.g., minimum cloud
decks) and in a manner (e.g., adherence to flight plans) that prevented the possibility
of data gaps. All QSI LiDAR systems are calibrated per the manufacturer and our
own specifications, and tested by QSI for internal consistency for every mission using
proprietary methods.
OLC Chelan Project Overview Map
OLC Chelan FEMA Data
LiDAR Acquisition Dates 7/31/2015 - 10/15/2015
Area of Interest 201,078 acres
Date Extent 215,029 acres
Projection Universal Transverse Mercator (UTM) 10 North
Horizontal Datum
Vertical Datum
NAD83 (2011), Epoch 2010.00
NAVD88 (Geoid 12A)
Aerial Acquisition
Vertical Accuracy
Vertical Accuracy Results Hard Surface
Sample Size (n) n = 123 GSPs
FVA (RMSE*1.96) 0.038 m (0.123 ft.)
Root Mean Square Error 0.019 m (0.063 ft.)
1 Standard Deviation 0.015 m (0.049 ft.)
2 Standard Deviations 0.039 m (0.127 ft.)
Average Deviation 0.014 m (0.044 ft.)
Minimum Deviation -0.080 m (-0.262 ft.)
Maximum Deviation 0.052 m (0.171 ft.)
Vertical Accuracy reporting is designed to meet
guidelines presented in the National Standard for Spatial
Data Accuracy (NSSDA) (FGDC, 1998) and the ASPRS
Guidelines for Vertical Accuracy Reporting for LiDAR Data
V1.0 (ASPRS, 2004). The statistical model compares known
ground survey points (GSPs) to the closest laser point.
Vertical accuracy statistical analysis uses ground survey
points in open areas where the LiDAR system has a “very
high probability” that the sensor will measure the ground
surface and reports the fundamental vertical accuracy
value (FVA=1.96*RMSE).
For the OLC Chelan FEMA study area, a total of 2,230
GSPs were collected. An additional 123 reserved ground
survey points were collected for independent verification,
resulting in a fundamental vertical accuracy (FVA) of 0.038 |