ABSTRACT

Images from agile (viewing angle over 40°) and very high spatial resolution satellites (inferior to 1 m) can be useful for monitoring cliff faces, which is the best proxy to better understand coastal cliff dynamics. However, these images with a specific configuration are rarely used, partly because it is cumbersome to process them. Based on Pléiades images of the coastal cliff face along the coast of Normandy, with a high angle of incidence (up to 40°) and taken on multiple dates, the paper aims to identify i) the best open-source processing chain to reconstitute three-dimensional (3D) cliff faces by stereo restitution ii) the reasons behind its best performance and iii) the key parameters to change depending on the image datasets or processing chains so as to facilitate transposition. The Ames Stereo Pipeline® (ASP®) and MicMac® software programmes were tested using different parameters (matching algorithm, size of correlation window, etc.) for the 3D reconstructions. MicMac® provides the best performance using GeomImage (1–2 pixel matching) with a size of correlation window of 3 × 3 or 7 × 7 associated with a regularization parameter of 0.10. With these parameters, the point clouds of the cliff face have an average point density of 1.70 point m⁻², a mean distance from Unmanned Aerial Vehicle (UAV) ground truth data of 0.04 m and a standard deviation of 1.72 m. With these characteristics, the threshold of rockfall detection using a multi-source comparison is assessed at 100 m³, which involves that the large majority of rockfalls (69%) around the study area could be detected by a diachronic approach. Considering the daily Pléiades revisiting time, this method offers a great opportunity to monitor erosion and to better understand coastal cliff dynamics.

摘要

来自敏捷（视角超过40°）和非常高空间分辨率的卫星（小于1 m）的图像可用于监视悬崖面，这是更好地了解沿海悬崖动态的最佳代理。但是，很少使用具有特定配置的这些图像，部分原因是处理它们很麻烦。基于诺曼底海岸的沿海悬崖面的l宿星图像，该入射角具有高入射角（最大40°）并在多个日期拍摄，本文旨在确定i）重构三者的最佳开源处理链立体复原的三维（3D）悬崖面ii）最佳性能背后的原因，iii）取决于图像数据集或处理链而改变的关键参数，以便于换位。使用3D重建的不同参数（匹配算法，相关窗口的大小等）对Ames StereoPipeline®（ASP®）和MicMac®软件程序进行了测试。MicMac®使用GeomImage（1-2个像素匹配）可提供最佳性能，相关窗口的大小为3×3或7×7，且正则化参数为0.10。使用这些参数，悬崖面的点云的平均点密度为1.70点m^-2，与无人飞行器（UAV）地面真实数据的平均距离为0.04 m，标准偏差为1.72 m。有了这些特征，使用多源比较的落石检测阈值估计为100 m ³，这涉及到可以通过历时方法来检测研究区域周围的大部分落石（69％）。考虑到每天P宿游的重游时间，这种方法为监测侵蚀和更好地了解沿海悬崖动态提供了一个很好的机会。