Woolpert Inc, Englewood, CO was contracted by the US Bureau of Reclamation to acquire detailed terrain data using airborne LiDAR technology, and digital orthoimagery for Salmon river (Challis valley) basin.
The LiDAR survey used a Leica ALS50 Phase II laser system. For the Trinity River survey site, the sensor scan angle was ±15o from nadir with a pulse rate designed to yield an average native density (number of pulses emitted by the laser system) of 6 points per square meter over terrestrial surfaces. All survey areas were surveyed with an opposing flight line side-lap of 50% (100% overlap) to reduce laser shadowing and increase surface laser painting. The Leica ALS50 Phase II system allows up to four range measurements (returns) per pulse, and all discernable laser returns were processed for the output dataset. To accurately solve for laser point and photo position (geographic coordinates x, y, z), the positional coordinates of the airborne sensor and the attitude of the aircraft were recorded continuously throughout the LiDAR collection mission. Aircraft position was measured twice per second (2 Hz) by an onboard differential GPS unit. Aircraft attitude was measured 200 times per second (200 Hz) as pitch, roll and yaw (heading) from an onboard inertial measurement unit (IMU). To allow for post-processing correction and calibration, aircraft/sensor position and attitude data are indexed by GPS time.
ASPRS Class II requirements for 2′ interval contours, reported as 0.6′ RMSE and 1.2′ at 95% confidence level specified by NSSDA was also produced through photogrammetric terrain extraction.