激光测高仪分米量级的绝对高程精度可以满足地面高程控制点的需求, 但其十几米甚至几十米的平面偏移使得其激光脚点仅能在平坦地表区域作为高程控制点使用。通过推导激光回波模型建立回波模型仿真器, 综合考虑激光能量时空分布、地表轮廓、地表反射率等器件和目标参数的影响, 对没有考虑地表反射率影响的现有波形匹配方法进行改进; 进而, 使用机载LiDAR点云数据和GLAS波形、能量数据, 以仿真波形和真实波形相关系数最大原则进行波形匹配, 寻找GLAS激光脚点中心坐标的精确位置。结果表明: 在GLAS系统接收能量正常的工作周期内, 波形匹配的平均相关系数大于0.9, 通过波形匹配提高GLAS激光脚点的平面精度, 能够实现约2 m的平面定位精度。研究方法能解决复杂地表条件下的激光高程控制点获取问题。

The footprints of a satellite laser altimeter have an elevation accuracy of the decimeter order, which satisfies the elevation accuracy needs of ground control points (GCP) for mapping. However, the horizontal accuracy of footprints is only few tens of meters, and only the footprints illuminating on flat ground targets can be used as GCPs. In this paper, the waveform model was derived and used to develop a waveform simulator of laser altimeters. Compared with the current method of waveform matching, the new simulator considered more detailed effects arising from the device and target, e.g., time and spatial distribution of lasers, surface profile, and surface reflectivity. The airborne LiDAR point cloud and the Geoscience Laser Altimeter System(GLAS) data were involved to match the best-fit waveform by maximizing the correlation coefficients of the simulated waveform and GLAS waveform, and the precise location of every GLAS footprint could be acquired where the correlation coefficient was the maximum. The results show that, the mean of maximum correlation coefficients is more than 0.9 during the GLAS operating periods with normal received energies, and the horizontal accuracy of footprints is approximately 2 m after the waveform matching. The proposed method can be used to extract the laser GCPs on complex relief of the surface.