DEM约束的卫星影像定位法

作为"云控制"摄影测量理论和方法的发展,研究了DEM约束的立体卫星影像区域网平差方法。与DEM仅作为高程控制信息使用,或者是通过DEM表面匹配实现绝对定向的间接定位方法不同,DEM作为平高控制信息被直接引入至基于RFM模型的卫星影像区域网平差之中。本文方法将连接点地面高程与DEM格网内插高程之差作为虚拟观测值构建约束方程,不仅利用了DEM高程信息,并且利用了其地形曲面包含的平面信息,以"云控制"方式在区域网平差过程中有效消除卫星影像RPC参数中包含的整体偏移及区域网内部的扭曲变形,实现了无地面控制点条件下卫星影像平面及高程绝对定位精度的大幅提升。使用覆盖山东全境的330景天绘一号立体卫星影像进行试验,分别以AW3D30、ASTER GDEM和SRTM GL3共3种开源DEM作为控制信息,并使用100个外业实测控制点进行精度评测。试验表明,以DEM作为控制可显著提高区域网平差的平面与高程精度,卫星影像绝对定位精度与DEM自身精度有关。当使用AW3D30作为控制时,可以取得与使用100个外业控制点平差同等精度,平面中误差为5.0 m(约1像素),高程中误差为2.9 m。试验结果证明了DEM替代外业控制点作为平差控制信息的有效性与可行性。

Using DEM as full controls in block adjustment of satellite imagery

An algorithm is proposed in this study which directly uses digital elevation model (DEM) as full controls in block adjustment of satellite images, it is an application and extension of "cloud control" in photogrammetry. Different from the indirect geo-referencing method based on the registration of image-derived DSM or DEM with reference DEM, a DEM is considered as full geometric constraints and directly introduced into the block adjustment of satellite images based on the RFM model, by minimizing the squared sum of distances from tie points to the terrain surface described by DEM. By using DEM as exclusive control, the horizontal and vertical positioning accuracies of stereo satellite images can be upgraded without any ground control points (GCPs). A total of 330 stereo scenes of Chinese Mapping Satellite-1 images covering the whole area of Shandong Province are used for experimental tests, and three different open source DEM data of 1″ grid AW3D30, ASTER GDEM and 3″ grid SRTM GL3 are used as control data, respectively. The adjustment results are validated by using 100 well-distributed ground check points. Experiments show that the positioning accuracy is depended on the accuracy of DEM itself. While using AW3D30 as full controls, which is the most accurate one among the three global DEMs in experiments, the block adjustment accuracy of 4.9 m (about 1 pixel) in horizontal direction and 2.8 m in vertical direction can be achieved, respectively. Which is similar with the results of using 100 GCPs. It is proved that the effectiveness and feasibility of using DEM instead of ground control points as controls for block adjustment.