Using Unoccupied Aerial Systems (UAS) equipped with optical RGB cameras and Doppler radar, surface velocity can be efficiently measured at high spatial resolution. UAS-borne Doppler radar is particularly attractive because it is suitable for real-time velocity determination, because the measurement is contactless, and because it has fewer limitations than image velocimetry techniques. In this paper, five cross-sections (XSs) were surveyed within a 10 km stretch of Rönne River in Sweden. Ground-truth surface velocity observations were retrieved with an electromagnetic velocity sensor (OTT MF Pro) along the XS at one m spacing. Videos from a UAS RGB camera were analyzed using both Particle Image Velocimetry (PIV) and Space-Time Image Velocimetry (STIV) techniques. Furthermore, we recorded full waveform signal data using a Doppler radar at multiple waypoints across the river. An algorithm fits two alternative models to the average amplitude curve to derive the correct river surface velocity based on Gaussian models with: (a) one peak, and (b) two peaks. Results indicate that river flow velocity and propwash velocity caused by the drone can be found in XS where the flow velocity is low, while the drone-induced propwash velocity can be neglected in fast and highly turbulent flows. To verify the river flow velocity derived from Doppler radar, a mean PIV value within the footprint of the Doppler radar at each waypoint was calculated. Finally, quantitative comparisons of OTT MF Pro data with STIV, mean PIV and Doppler radar revealed that UAS-borne Doppler radar could reliably measure the river surface velocity.

中文翻译：

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使用 UAS 机载多普勒雷达测量河面速度


使用配备光学 RGB 摄像头和多普勒雷达的无人航空系统 （UAS），可以在高空间分辨率下有效地测量表面速度。UAS 机载多普勒雷达特别有吸引力，因为它适用于实时速度测定，因为测量是非接触式的，而且它比图像测速技术的限制更少。在本文中，在瑞典 Rönne 河 10 公里的范围内调查了 5 个横截面 （XS）。使用电磁速度传感器 （OTT MF Pro） 沿 XS 以 1 m 的间距检索地面真实表面速度观测值。使用粒子图像测速 （PIV） 和空时图像测速 （STIV） 技术分析来自 UAS RGB 相机的视频。此外，我们使用多普勒雷达在河流对岸的多个航路点记录了完整的波形信号数据。该算法将两个备选模型拟合到平均振幅曲线上，以根据高斯模型得出正确的河面速度：（a） 一个峰值，（b） 两个峰值。结果表明，在流速较低的 XS 中可以发现由无人机引起的河流流速和螺旋桨速度，而在快速和高度湍流中可以忽略无人机引起的螺旋桨速度。为了验证多普勒雷达得出的河流流速，计算了多普勒雷达在每个航路点的足迹内的平均 PIV 值。最后，OTT MF Pro 数据与 STIV 、均值 PIV 和多普勒雷达的定量比较表明，无人机机载多普勒雷达可以可靠地测量河面速度。