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Surf zone characterization from Unmanned Aerial Vehicle imagery

机译：无人机图像对冲浪区的表征

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We investigate the issues and methods for estimating nearshore bathymetry based on wave celerity measurements obtained using time series imagery from small unmanned aircraft systems (SUAS). In contrast to time series imagery from fixed cameras or from larger aircraft, SUAS data are usually short, gappy in time, and unsteady in aim in high frequency ways that are not reflected by the filtered navigation metadata. These issues were first investigated using fixed camera proxy data that have been intentionally degraded to mimic these problems. It has been found that records as short as 50 s or less can yield good bathymetry results. Gaps in records associated with inadvertent look-away during unsteady flight would normally prevent use of the required standard Fast Fourier Transform methods. However, we found that a full Fourier Transform could be implemented on the remaining valid record segments and was effective if at least 50% of total record length remained intact. Errors in image geo-navigation were stabilized based on fixed ground fiducials within a required land portion of the image. The elements of a future method that could remove this requirement were then outlined. Two test SUAS data runs were analyzed and compared to survey ground truth data. A 54-s data run at Eglin Air Force Base on the Gulf of Mexico yielded a good bathymetry product that compared well with survey data (standard deviation of 0.51 m in depths ranging from 0 to 4 m). A shorter (30.5 s) record from Silver Strand Beach (near Coronado) on the US west coast provided a good approximation of the surveyed bathymetry but was excessively deep offshore and had larger errors (1.19 m for true depths ranging from 0 to 6 m), consistent with the short record length. Seventy-three percent of the bathymetry estimates lay within 1 m of the truth for most of the nearshore.
机译：我们研究了基于波速测量的近海测深法的问题和方法，这些波速测量是使用小型无人飞机系统（SUAS）的时间序列图像获得的。与来自固定摄像机或大型飞机的时间序列图像相反，SUAS数据通常较短，时空不清，并且目标频率不稳定，无法通过过滤的导航元数据反映出来。首先使用固定的摄像机代理数据调查了这些问题，这些数据有意降级以模拟这些问题。已经发现，短至50秒或更短的记录可以产生良好的测深结果。与不稳定飞行过程中无意中的视线相关联的记录中的空白通常会阻止使用所需的标准快速傅里叶变换方法。但是，我们发现可以在其余有效记录段上执行完整的傅立叶变换，并且如果至少保留总记录长度的50％，则该傅立叶变换是有效的。基于图像所需陆地部分内固定的地面基准，可以稳定图像地理导航中的错误。然后概述了可以消除此要求的将来方法的元素。分析了两次测试SUAS数据运行并将其与调查地面真实数据进行比较。在墨西哥湾Eglin空军基地进行的54秒钟数据运行产生了良好的测深仪产品，与调查数据（标准偏差为0到4 m，深度为0.51 m）相比，效果很好。美国西海岸的银线滩（在科罗纳多附近）的短记录（30.5 s）提供了良好的测深数据，但离岸深度过大，误差较大（0至6 m的真实深度为1.19 m） ，与短记录长度一致。对于大多数近岸，总测深的百分之七十三位于真相的1 m以内。

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