Unmanned Aerial System (UAS) observations of water surface elevation in a small stream: Comparison of radar altimetry, LIDAR and photogrammetry techniques
Unmanned Aerial System (UAS) observations of water surface elevation in a small stream: Comparison of radar altimetry, LIDAR and photogrammetry techniques
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DOI：
10.1016/j.rse.2019.111487
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发表时间：
2020-02-01
影响因子：
13.5
通讯作者：
Bauer-Gottwein, Peter
中科院分区：
文献类型：
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作者：
Bandini, Filippo;Sunding, Tanya Pheiffer;Bauer-Gottwein, Peter
水面高程（WSE）是一个重要的水文观测，可用于校准水文模型，预测洪水和评估气候变化。然而，全世界现场测量站的数量正在减少。卫星测高，包括最近发射的卫星任务（例如雷达测高任务Cryosat 2，Jason 3，Sentinel 3A/B和激光雷达使命ICESat-2），可以确定WSE仅在河流中，超过ca。100米宽。小溪流的水环境质量测量目前仍然局限于现有的几个原位站或耗时的原位调查。无人机系统（UAS）可以在水文关注期间（但在极端天气条件下有飞行限制）、在短的调查时间内并通过自动或半自动飞行操作获取实时WSE观测结果。UAS承载的摄影测量是一种众所周知的技术，可以以高达几厘米的精度估计陆地高程，类似地，UAS承载的LIDAR可以估计陆地高程，但不需要地面控制点（GCPs）。然而，这两种技术在估计WSE方面都面临局限性：水的透明度和水面（WS）上缺乏稳定的视觉关键点使UAS承载的WSE摄影测量估计复杂化，而来自水面的LIDAR反射通常不足以被目前市场上大多数UAS承载的LIDAR系统捕获。因此，激光雷达和摄影测量通常需要提取“水边缘”点（即陆地和水之间的界面处的点）的高程，以识别WSE。我们使用新的雷达测高解决方案展示了高度精确的WSE观测，该解决方案包括具有全波形分析的77 GHz雷达芯片和精确的双频差分全球导航卫星系统（GNSS）系统。雷达测高解决方案显示了WSE估计的最低标准差（sigma）和RMSE，约。1.5 cm和ca. 3厘米，而摄影测量和激光雷达显示在分米级的西格玛和RMSE。与激光雷达相比，雷达测高还需要显著更短的调查和处理时间，特别是与摄影测量相比。
Water Surface Elevation (WSE) is an important hydrometric observation, useful to calibrate hydrological models, predict floods, and assess climate change. However, the number of in-situ gauging stations is in decline worldwide. Satellite altimetry, including the recently launched satellite missions (e.g. the radar altimetry missions Cryosat 2, Jason 3, Sentinel 3A/B and the LIDAR mission ICESat-2), can determine WSE only in rivers which are more than ca. 100 m wide. WSE measurements in small streams currently remain limited to the few existing in-situ stations or to time-consuming in-situ surveys. Unmanned Aerial Systems (UAS) can acquire real-time WSE observations during periods of hydrological interest (but with flight limitations in extreme weather conditions), within short survey times and with automatic or semi-automatic flight operations. UAS-borne photogrammetry is a well-known technique that can estimate land elevation with an accuracy as high as a few cm, similarly UAS-borne LIDAR can estimate land elevation but without requiring Ground Control Points (GCPs). However, both techniques face limitations in estimating WSE: water transparency and lack of stable visual key points on the Water Surface (WS) complicate the UAS-borne photogrammetric estimates of WSE, while the LIDAR reflection from the water surface is generally not strong enough to be captured by most of the UAS-borne LIDAR systems currently available on the market. Thus, LIDAR and photogrammetry generally require extraction of the elevation of the "water-edge" points, i.e. points at the interface between land and water, for identifying the WSE. We demonstrate highly accurate WSE observations with a new radar altimetry solution, which comprises a 77 GHz radar chip with full waveform analysis and an accurate dual frequency differential Global Navigation Satellite System (GNSS) system. The radar altimetry solution shows the lowest standard deviation (sigma) and RMSE on WSE estimates, ca. 1.5 cm and ca. 3 cm respectively, whilst photogrammetry and LIDAR show a sigma and an RMSE at decimetre level. Radar altimetry also requires a significantly shorter survey and processing time compared to LIDAR and especially to photogrammetry.