**2.1 Basic principle**

The satellite-based LiDAR measurement is performed by transmitting laser pulses at a certain frequency from the satellite-based laser to the ground, and the laser beam crosses the atmosphere and is scattered by the terrain surface, producing a weak backscattered echo, which is received by the telescope on the satellite-based LiDAR, and the distance value between the laser and the detection target is calculated through photoelectric signal conversion and time measurement, and then combined with the information of satellite attitude, platform position, and laser pointing to finally obtain precise three-dimensional spatial coordinates of the laser footprint point, as shown in **Figure 2**. The satellite-based LiDAR measurement belongs to the direct active acquisition of surface elevation information, which is different from the traditional indirect reconstruction measurement mode of remote sensing imaging mapping, reducing the time of post-processing process and improving the efficiency of surface 3D information acquisition.
