Section 6: Conducting the Section 6: Conducting the Lidar SurveyLidar Survey

Outline GPS base station

operation Aircraft operations

mapping survey areacalibration

Preliminary processing and checks for data completeness

Ground 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 systemA. Laser and IMU, B. Computer/equipment rackC. 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

0 2 mi

2 km0

Gulf of Mexico

Kinematic surveydata points

Calibration aircrafttrajectory

Shoreline aircrafttrajectory

Galvestoncounty roads

Environmentalsensitivity index

Preliminary Processing

Preliminary processing of aircraft trajectories

Trajectories 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

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

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