|2008 St. Johns County, FL Countywide Lidar
|Airborne terrestrial LiDAR was collected for St. Johns County, FL. System Parameters/Flight
Plan. The LiDAR system acquisition parameters were developed based on a maximum average
ground sample distance of 2.1 feet. A Leica ALS50 LiDAR sensor was used for acquisition.
Acquisition specifications for the sensor follows: Field of View (full angle) - 24
degrees, Nominal flight altitude (AGL) - 3000 feet, Airspeed - 130 mph (113 knots),
Laser pulse rate - 100,000 Hz, Nominal swath width (on ground) - 1275 feet, Maximum
cross track point spacing - 2.07 feet, Maximum along track point spacing - 4.30 feet,
Average point spacing - 1.67 feet, Flight line spacing - 970.47 feet, Side overlap
- 23.91 percent. LiDAR System Calibration. Prior to the LiDAR acquisition, the system
underwent a calibration to verify the operational accuracy and misalignment angles.
Boresight calibrations were performed for the LiDAR system at the beginning and end
of each flight mission. LiDAR Data Acquisition. LiDAR data acquisition only occurred
when the sky was sufficiently clear of clouds, smoke, and atmospheric haze. The LiDAR
data was processed immediately after the acquisition to verify the coverage had no
voids. GPS/Inertial Measurement Unit (IMU) Post Processing. 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. LiDAR Processing and Classification. The LiDAR
data was post processed and verified to be consistent with the project requirements
in terms of post spacing and absence of artifacts. The point cloud underwent classification
to determine bare-earth points (class 2), noise points (class 7), water returns (class
9), and unclassified data (class 1). Class 12 contains LiDAR points removed from the
overlap region between adjacent flight lines.