控制点布设对冰川区无人机摄影测量精度的影响

Influence of the use of photogrammetric measurement precision on low-altitude micro-UAVs in the glacier region

冰川监测是冰冻圈科学研究中的一项重要基础内容,获取高质量冰川DEM和DOM数据是研究的基础。随着无人机技术的兴起,给冰川监测提供了全新的技术手段,然而冰川区开展无人机摄影测量时,地面控制点的布设与测量成为能否获取高精度数据产品的关键,而山地冰川往往伴随着地形复杂,行走困难,野外实地测量难以全面实施等不利因素。本研究中以位于祁连山西段大雪山地区的老虎沟12号冰川末端部分为研究区域,设计实施了多种控制点布设方案,使用低空微型无人机飞行3个架次,获取研究区航摄影像。通过对比控制点在不同分布情况及数量情况下,DEM和DOM数据检查点的精度,评价不同控制点布设方案的可行性。对比结果显示,在航飞过程中使用单格网模式即可获取高精度的影像数据;实施地面控制作业时,使用5—7个控制点均匀分布在测量区即可获取较高精度的图像数据;当冰川区不能满足均匀布设控制点时,可沿冰川主流线布设足够数量的控制点,所得图像精度也可以满足冰川学研究要求;若只能在冰川中下部或者中上部布设控制点,则控制点应覆盖冰面起伏较大的区域。

In the global warming background, glaciers around the world remarkably shrunk. Glacier monitoring is an important part of cryosphere science. High-quality DEM and DOM were the primary data in glacier research. In recent years, the rapid development of the technicality of UAV provided a new platform for observing glacier. The control point was usually unevenly distributed on glacier surface because of complex and inaccessible surface conditions. Thus, this study set 17 control points on the lower part of the Laohugou Glacier No.12. Aerial photography images were acquired by low-altitude micro-UAV covered ice tongue. Pix4D Capture was used as route planning software, and all images and control points were processed by Pix4D Mapper software. In processing, different numbers and distribution modes were used, and the accuracy of every DEM and DOM were checked. Pix4D Capture has two route planning modes, namely, single grid and double grid. The two route planning modes have the same accuracy. In ice tongue, five control points are evenly distributed, and high precision image data could be obtained. If enough control points are distributed along with the main flow line of the glacier, then the image precision is acceptable. If the control points are mainly distributed at the mid-upper or mid-lower parts of the glacier, then control point should cover the fluctuation region of the ice surface.