1. Introduction . Airborne lidar technology, as an important air-to-ground observation technology [ 1 – 3 ], is playing an increasingly important role in many applications such as forest remote sensing [ 4 ], environmental monitoring [ 5 ], urban planning [ 6 ], and ocean exploration [ 7 , 8 ] through active laser remote sensing detection, combined with technologies such as global positioning system and inertial measuring unit. As the core means of Earth observation, remote se...