Collister Brian L, Zimmerman Richard C, Hill Victoria J, Sukenik Charles I, Balch William M
Appl Opt. 2020 May 20;59(15):4650-4662. doi: 10.1364/AO.389845.
Oceanographic lidar can provide remote estimates of the vertical distribution of suspended particles in natural waters, potentially revolutionizing our ability to characterize marine ecosystems and properly represent them in models of upper ocean biogeochemistry. However, lidar signals exhibit complex dependencies on water column inherent optical properties (IOPs) and instrument characteristics, which complicate efforts to derive meaningful biogeochemical properties from lidar return signals. In this study, we used a ship-based system to measure the lidar attenuation coefficient () and linear depolarization ratio () across a variety of optically and biogeochemically distinct water masses, including turbid coastal waters, clear oligotrophic waters, and calcite rich waters associated with a mesoscale coccolithophore bloom. Sea surface IOPs were measured continuously while underway to characterize the response of and to changes in particle abundance and composition. The magnitude of was consistent with the diffuse attenuation coefficient (), though the versus relationship was nonlinear. was positively related to the scattering optical depth and the calcite fraction of backscattering. A statistical fit to these data suggests that the polarized scattering properties of calcified particles are distinct and contribute to measurable differences in the lidar depolarization ratio. A better understanding of the polarized scattering properties of coccolithophores and other marine particles will further our ability to interpret polarized oceanographic lidar measurements and may lead to new techniques for measuring the material properties of marine particles remotely.
海洋激光雷达能够对天然水体中悬浮颗粒的垂直分布进行远程估算，这有可能彻底改变我们表征海洋生态系统以及在海洋上层生物地球化学模型中准确呈现这些系统的能力。然而，激光雷达信号对水柱固有光学特性（IOPs）和仪器特性表现出复杂的依赖性，这使得从激光雷达回波信号中推导有意义的生物地球化学特性变得复杂。在本研究中，我们使用了一个船基系统，在各种光学和生物地球化学性质不同的水体中测量激光雷达衰减系数（）和线性偏振比（），这些水体包括浑浊的沿海水域、清澈的贫营养水域以及与中尺度颗石藻大量繁殖相关的富含方解石的水域。在航行过程中持续测量海面的IOPs，以表征和对颗粒丰度及组成变化的响应。的大小与漫衰减系数（）一致，尽管与的关系是非线性的。与散射光学深度和后向散射的方解石含量呈正相关。对这些数据的统计拟合表明，钙化颗粒的偏振散射特性是独特的，并且导致激光雷达偏振比出现可测量的差异。更好地理解颗石藻和其他海洋颗粒的偏振散射特性，将提升我们解释偏振海洋激光雷达测量结果的能力，并可能带来远程测量海洋颗粒物质特性的新技术。
