Study On The Flight Calibration Technology Based On The Light Detection And Ranging System

Airborne Light Detection And Ranging(LiDAR)is an active remote sensing technology for acquiring three dimensional(3D)information of the terra effectively.There are many advantages,such as high accuracy,less field work,operation at night and penetration through foliage.Airborne LiDAR has been widely used in topographic mapping,3D city modelling,power line inspection and vegetation parameters estimation.However,the coordinates of laser point can be affected by many errors easily due to some specialties of airborne LiDAR,such as multi system integration,direction georeference,discreteness and irregularity of data Especially,the system errors should be calibrated rigorously to guarantee the geometric precision.The main contents and contributions of this paper are as follows:(1)According to the airborne LiDAR georeferenced principle,the coordinate frame transformation from the raw observation to 3D coordinates of laser points and the geolocation equation were deduced.Then the error sources of airborne LiDAR were introduced and their effects were analyzed quantitatively and qualitatively based on the error joint propagation law of random and system errors.Three methods of eliminating errors.(2)The IMU angular deviation was checked by using the manual calibration method.According to the target objects,by choosing the different course,the IMU angular deviations were gradual separated on the roll,pitch and yaw axes.The values of IMU deviation were then calculated based on the multi-iterated empirical formula.(3)In view of the low automation level on the calibration of IMU angular deviation,this paper proposed an automatic method.The ground points were removed by using the points cloud filtering,and the building objects were extracted based on the distance clustering method.The roof plane was then segmented by RANSAC algorithm,to realizing the matching of the connection planes.Finally,the distance between the point and the reference plane was calculated by using the coplanar constraint condition,and the IMU angular deviation was obtained by following the adjustment-calculation model,and verified by the actual flight data.(4)Two principles,"symmetry" and "low correlation" for the planar patches configuration were proposed to decrease the correlation of three boresight angles and increase the reliability of the calibration results.