An Approach to Determining Turbidity and Correcting for Signal Attenuation in Airborne Lidar Bathymetry
An Approach to Determining Turbidity and Correcting for Signal Attenuation in Airborne Lidar Bathymetry
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DOI：
10.1007/s41064-016-0001-0
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发表时间：
2017-02-01
影响因子：
4.1
通讯作者：
Weiss, Robert
中科院分区：
文献类型：
--
作者：
Richter, Katja;Maas, Hans-Gerd;Weiss, Robert
机载激光雷达测深是测量浅水体底部的有效技术。激光雷达测深光束传播的一个特征是水柱中的散射和吸收效应，这两种效应都会导致接收信号强度的损失。这种信号强度的损失取决于水体的浊度。相反，对记录的波形信号的衰减进行分析可以得出关于水中局部浊度的陈述。该论文展示了通过分析记录的波形并拟合指数函数来确定每个激光脉冲的一个浊度测量值的第一种方法，其中衰减系数描述了描述浊度的积分测量值。该技术应用于浅层内陆水域，并通过传统的逐点浊度测量技术验证了结果。激光雷达测深中信号强度衰减和损失的一个明显后果是底部回波变得相当弱。在很多情况下，传统的地面脉冲回波检测技术无法检测到水体底部点，导致水体底部点的数量减少，从而限制了该技术的应用范围。为了部分补偿这种影响，开发了一种基于差分反向散射截面确定的信号衰减校正方法，该方法允许对地面信号进行源自信号的重新放大。尽管该技术也会放大噪声，但可以证明它能够提供更多数量的附加接地点，从而扩展该技术的适用性。
Airborne lidar bathymetry is an efficient technique for measuring the bottom of shallow water bodies. A characteristical feature of lidar bathymetry beam propagation is given by scattering and absorption effects in the water column, both leading to a loss of received signal intensity. This loss of signal intensity depends on the turbidity of the water body. Inversely, an analysis of the decay of the recorded waveform signal allows for deriving statements on the local degree of turbidity in the water. The paper shows a first approach on the determination of one turbidity measure per laser pulse by analysing the recorded waveform and fitting an exponential function, wherein the decay coefficient depicts an integral measure describing turbidity. The technique was applied to a shallow inland water, and the results were validated by conventional point-wise turbidity measurement techniques. An obvious consequence of attenuation and loss of signal intensity in lidar bathymetry is the fact that the bottom returns become rather weak. In many cases, conventional ground pulse echo detection techniques fail in detecting water bottom points, leading to a reduced number of water body bottom points and thus limiting the application range of the technique. To partly compensate for this effect, a differential backscatter cross section determination based signal attenuation correction method has been developed, which allows for a signal-derived re-amplification of the ground signal. Although the technique also amplifies noise, it could be shown that it is capable of delivering a higher number of additional ground points and thus extending the applicability of the technique.