Section 6: Conducting the Lidar Survey

1. Section 6: Conducting the Lidar Survey

2. Outline • GPS base station operation • Aircraft operations mapping survey area calibration • Preliminary processing and checks for data completeness • Ground GPS data collection

3. 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

4. ALTM system A. Laser and IMU, B. Computer/equipment rack C. Ashtech Z-12 GPS receiver. 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

5. Aircraft Operations Mapping shoreline using video camera

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

7. Calibration Flight Lines

8. Preliminary Processing • Preliminary processing of aircraft trajectories • Trajectories are usually accurate to within 10cm of the true position of the aircraft

9. Data Coverage Check Galveston, Texas West Bay Area Galveston Bay, Texas • West Bay Area

10. Data Coverage

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

12. Ground GPS Survey • Methodology 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