Hu Lianbo, Zhang Xiaodong, Xiong Yuanheng, Gray Deric J, He Ming-Xia
Appl Opt. 2020 Apr 1;59(10):C31-C41. doi: 10.1364/AO.383229.
Properly interpreting lidar (light detection and ranging) signal for characterizing particle distribution relies on a key parameter, (), which relates the particulate volume scattering function (VSF) at 180° (()) that a lidar measures to the particulate backscattering coefficient (). However, () has been seldom studied due to challenges in accurately measuring () and concurrently in the field. In this study, (), as well as its spectral dependence, was re-examined using the VSFs measured in situ at high angular resolution in a wide range of waters. (), while not measured directly, was inferred using a physically sound, well-validated VSF-inversion method. The effects of particle shape and internal structure on the inversion were tested using three inversion kernels consisting of phase functions computed for particles that are assumed as homogenous sphere, homogenous asymmetric hexahedra, or coated sphere. The reconstructed VSFs using any of the three kernels agreed well with the measured VSFs with a mean percentage difference <5 at scattering angles <170. At angles immediately near or equal to 180°, the reconstructed () depends strongly on the inversion kernel. () derived with the sphere kernels was smaller than those derived with the hexahedra kernel but consistent with () estimated directly from high-spectral-resolution lidar and in situ backscattering sensor. The possible explanation was that the sphere kernels are able to capture the backscattering enhancement feature near 180° that has been observed for marine particles. () derived using the coated sphere kernel was generally lower than those derived with the homogenous sphere kernel. Our result suggests that () is sensitive to the shape and internal structure of particles and significant error could be induced if a fixed value of () is to be used to interpret lidar signal collected in different waters. On the other hand, () showed little spectral dependence.
正确解释用于表征粒子分布的激光雷达（光探测与测距）信号依赖于一个关键参数（），该参数将激光雷达在180°测量的粒子体积散射函数（VSF）（）与粒子后向散射系数（）相关联。然而，由于在现场准确测量（）和同时测量（）存在挑战，（）很少被研究。在本研究中，使用在广泛水域中以高角度分辨率原位测量的VSF重新审视了（）及其光谱依赖性。（）虽然没有直接测量，但使用一种物理上合理且经过充分验证的VSF反演方法进行了推断。使用由为假定为均匀球体、均匀不对称六面体或包覆球体的粒子计算的相位函数组成的三个反演核，测试了粒子形状和内部结构对反演的影响。使用这三个核中的任何一个重建的VSF与测量的VSF在散射角<170°时平均百分比差异<5，吻合良好。在紧邻或等于180°的角度处，重建的（）强烈依赖于反演核。用球体核得出的（）小于用六面体核得出的（），但与从高光谱分辨率激光雷达和原位后向散射传感器直接估计的（）一致。可能的解释是球体核能够捕捉到海洋粒子在180°附近观察到的后向散射增强特征。使用包覆球体核得出的（）通常低于用均匀球体核得出的（）。我们的结果表明（）对粒子的形状和内部结构敏感，如果使用固定值的（）来解释在不同水域收集的激光雷达信号，可能会引起显著误差。另一方面，（）几乎没有光谱依赖性。
