We have studied the possible advantages of a wide-area approach (long-baseline differential positioning with GPS) for the precise kinematic trajectory determination of aircraft in support of airborne scanning lidar altimeter surveys, over the usual and more labor and resource intensive short-baseline approach with locally deployed ground receivers. In this form of remote sensing, the GNSS data are used to find very precisely the aircraft position and, combining it with inertial data, the aircraft orientation, in order to georeference the scanning laser measurements within very strict tolerances.udIf proved useful, the adoption of the wide-area approach, compared to present practice, could result in a substantial reduction of costs and in more flexibility when confronted with changing weather conditions or dealing with priority response situations. Such situations, at present, may require postponing a survey, or redeploying ground receivers and personnel on short notice.udWe have conducted three successful tests: two with data collected during the survey of large areas in the northeast of the state of New South Wales, in Australia, and a third one with data from a system calibration flight over a pre-surveyed area around the Bathurst airport, also in that state. udThese tests were organized and conducted by the NSW Government’s Land and Property Management Authority (LPMA), in collaboration with the University of New South Wales, in June of 2009 and July of 2010. The baselines from the reference stations to the aircraft were as long as 1100 km.udThe wide-area reference stations used in the tests are part of CORSnet-NSW, a network of continuously operating reference stations run by LPMA in the state of New South Wales. As of September of 2010 this network consisted of 43 stations; and the goal is to reach a total of 70 by 2012. All receivers in the network collected data at the rate of 1 Hz; on the aircraft 2 Hz data were collected. The solutions were calculated in post-processing mode, at 2 Hz.udTo verify the quality of the aircraft trajectories determined by the wide-area technique, they were compared to the customary short-baseline solutions with local reference stations set up within a few kilometers of the flight path of the airplane. Finally, the digital elevation model (DEM) obtained from the calibration flight data and a precise wide-area GNSS trajectory was compared to the DEM made with the usual short-baseline method. In all cases the agreement was excellent.
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