The Application Of GPS In Airborne Lidar Technology

This paper, combined with actual project, uses airborne IMU parameters and carrier Doppler shift observations by GPS which are provided by the Applanix laser equipment to generate the aircraft speed and trajectory, and utilizes the least squares method to process the GPS and IMU observations to get the aircraft roll, pitch, position and other parameters, then takes advantages of the real-time kinematic GPS positioning software in POSPac and GAMIT/GLOBK (Version10.2) high-precision static GPS positioning software to complete some specific research work. The key points of the research are:1. ground base station layout and data processing methods of airborne LIDAR;2. applications of Differential GPS in airborne LIDAR trajectory;3. applications of Precise Point Positioning (PPP) in the airborne LIDAR.This paper, combined with airborne LIRDA scanning characteristic, presents the layout scheme of the GPS ground reference stations and associated measurement methods, and describes in detail for the ground GPS base station data processing software GAMIT/GLOBK and parameters analysis, at the same time gives a brief discussion of accuracy evaluation method and the Kalman filter method. At last introduces the POSPac module which is used for LIDAR trajectory solution and the principles, and processes a sortie data in survey region and gives result analysis.POSPac uses airborne GPS and IMU data to obtain GPS differential solution. The principles are the same with conventional GPS differential,while the difference is that conventional differential GPS requires static observation, and airborne differential needs to set up a certain number of terrestrial base station which will be simultaneously observed as the ground base station GPS (static) with the airborne GPS (dynamic) when airborne laser scanning; When solving trajectory, the airborne GPS coordinates at some point is obtained via the ground GPS differentiation, and then these continuous coordinates will create the flight path of the airborne laser. This paper provides a detailed description of the important parameter settings in the trajectory solution and the accuracy assessment indicators of results through the actual project.Finally, this paper processes the data (POS and airborne GPS) collected in three regions with DGPS and PPP method respectively to generate two different trajectories and to make statistical analysis between trajectory differences, The results show that there is a systematic bias between two solutions, but different in each sortie. The systematic bias of the trajectory is less in horizontal direction(NE)than in vertical direction (H), and the systematic bias oscillates periodically in different strips because the aircraft speed changing suddenly while turning makes the IMU system error bigger. In the future actual project, it is necessary to identify the validity and reliability of PPP method to improve the operating efficiency of airborne LIDAR in difficult area.