Section 6: Conducting the Lidar Survey

Outline QGPS base station operation QAircraft operations mapping survey area calibration QPreliminary processing and checks for data completeness QGround GPS data collection

GPS Base Station Operation  Minimum of two GPS base stations must be operating during the lidar survey (optimal time frame: starting 30min before takeoff running until 30min after landing of the aircraft)  Best if survey aircraft stays within 30-50km of one base station at all times  Base station and aircraft GPS files are merged to obtain a differentially corrected solution for the aircraft trajectory

Aircraft Operations  Pilot must restrict roll (bank) angle to <15deg or you lose lock on GPS satellites and increase difficulty of obtaining a carrier phase solution for aircraft trajectory ALTM system A. Laser and IMU, B. Computer/equipment rack C. Ashtech Z-12 GPS receiver.

Aircraft Operations Mapping shoreline using video camera

Aircraft Operations LANDSAT image of Bonneville Salt Flats (BSF) with orthogonal flight lines

Calibration Flight Lines

Preliminary Processing QPreliminary processing of aircraft trajectories QTrajectories are usually accurate to within 10cm of the true position of the aircraft

Data Coverage Check Galveston, Texas West Bay Area Galveston Bay, Texas West Bay Area

Data Coverage

Ground Truth GPS Survey QGround GPS surveys provide “ground truth” QKinematic surveys conducted using same base stations as the lidar survey QUsed to estimate biases in lidar data Red points are from kinematic ground GPS survey along paved road next to runway superimposed on lidar DEM

Ground GPS Survey QMethodology for conducting kinematic ground GPS surveys Walk long distances with backpack GPS unit Mount antenna on car roof and drive slowly up and down road many times