A New Laser Point Offsets Eliminating Method for Airborne LiDAR by Compensating Laser Pointing Deviations
X. Tian, L. Xu, T. Xu and L. Jing
When the airborne light detection and ranging (LiDAR) instrument is in operation, the flight platform is expected to be in uniform linear motion, thus the obtained laser points distribute approximately uniformly on the ground. Unfortunately, due to existence of engine vibration and airflow disturbance, etc., the flight platform cannot be kept in ideal uniform linear motion in actual applications, which makes the platform attitude nonstationary and deviate from the planned route. As a result, the laser points deviated from the ideal positions, and distribute disorderly on the ground. In order to eliminate the influence of the attitude disturbances on the distribution of laser points, a new compensation method for laser pointing deviations was proposed. The scanning mirror was fixed on the centre of a two-axis compensation device that was ever constructed by the research group to which the authors belong. The normal direction of the scanning mirror can be changed to keep the reflected light along ideal direction and hence counteract the influence caused by attitude disturbances. The compensation method can be implemented in the following three steps: (i) Measure the attitude disturbances and the scanning angle using the inertial measurement unit (IMU) and the angle encoder in real time, respectively; (ii) calculate the required rotation angles of the inner and outer frames of the two-axis compensation device according to the attitude disturbances and the scanning angle; and (iii) rotate the inner and outer frames of the compensation device to the expected angle positions. To validate the new compensation method, numerical simulations and physical experiments were both carried out. The obtained results demonstrated that the laser point offsets have been greatly eliminated.
Keywords: LiDAR, airborne, laser points distribution, attitude disturbances, laser pointing deviations, compensation