Planning for airborne LIDAR survey Dr Lamyaa Gamal

Planning for airborne LIDAR survey Dr. Lamyaa Gamal El-deen

u Minimize baseline: <30 km u Minimize multipath of rover and reference station (reflections of the GPS Signals) u Minimize Dilution of Precission (DOP) u Multiple base stations at a known location (take usually 2 reference stations for redundancy) to provide redundancy and backup in case one of the GPS receivers fails. u GPS-data from the reference station in

the original format and not in a converted format like RINEX u Important for the processing: WGS 84 Coordinates (lambda, phi, h) of the reference station and the Instrument Height of the receiver u The reference station must log the GPSdata with 1 s rate u The reference station must be a dual frequency receiver u The elevation cut off angle of the station must be ~5° u Stop aircraft away from hangar and other obstructions (Multipath)

In-Flight Procedures for a high navigation solution in the post processing: u aircraft is flying straight and level: fly 4 min straight on and then fly a S-turn u repeat this procedure after a potential loss of lock GPS-Constellation during a Laserscan mission: u The reference station should be near the scan area (max. 30 km away) u The aircraft should fly one turn over the reference station (fixing ambiguities) If the reference station is more than 30 km away from the scan area: u after take off: fly a turn over the reference station and then into the scan area u after mission: fly another turn over the reference station before landing

Since the positioning of the LIDAR sensor relies on the GPS, specifically the kinematic solution of L 1/L 2 carrier phase processing, satellite ambiguity resolution must occur from data collected during times of low Position Dilution of Precision (PDOP), less than five. Most GPS postprocessing packages include mission planning software for checking PDOP and the number of satellites available for a specified time period. u Ensure that receivers on ground and on the aircraft works simultaneously u It is important that the control points used have the required horizontal and vertical accuracy to meet the need of the project accuracy. u Make a cross flight : The primary function of the cross flight is to detect systematic errors u

In general, flight lines are created to provide a 30% overlap of the previous flight line collection swath with the current lines swath

Quality Control u Comparisons between ground stations: The use of two ground control stations can allow for processing of GPS data between both stations to check for agreement of the published coordinate values for each station. The kinematic trajectory from each station to the aircraft can be processed and compared to each other to determine if the differences are within the accuracy tolerance or not. If one control point is closer to the project site than the other, then it is expected that there will be slight differences in the two DGPS trajectory solutions.

u Ground truth data collection: The intensity image produced from the LIDAR collection or the image from a digital camera, if it was operated during the collection, can be used to pick areas where ground truth data collection could be collected.