Abstract: This study aims at the problem that the monitoring accuracy of the same aerial survey aircraft varies greatly due to the topographic relief when the traditional UAV conducts subsidence monitoring in mining area. In this paper, the influence of terrain change on the resolution, photo overlap and monitoring accuracy of the shooting image was analyzed. The TOF sensor was installed on the UAV, and the PID controller was coded to maintain the same height and stable flight relative to the ground, thus realizing the UAV terrain following monitoring. The results show that the terrain fluctuation will reduce the monitoring accuracy of the traditional UAV, but the method proposed in this paper can improve its accuracy, so that the UAV can follow the aerial survey and ensure the monitoring accuracy. Meanwhile, in mining areas with complex terrain, the average precision of traditional UAV for subsidence monitoring is 65.73 mm, making the average precision of UAV with terrain following technology for subsidence monitoring reach 46.59 mm, and greatly improving the detection accuracy of UAV. Compared with the observation line data in the field, the results can predict the subsidence trend accurately, but can not accurately capture the subtle changes of the surface. Thus, the obtained subsidence scope can comprehensively and extensively reflect the area affected by the subsidence which caused by the advance of the working face. Therefore, the research results can provide reference for mining subsidence monitoring.

Key words: mining subsidence, UAV, terrain following, time of flight sensor, photogrammetry