Collaborative Research: Inferring Marine Particle Properties from Polarized Volume Scattering Functions

了解生物地球化学循环及其与气候系统的相互作用需要对全球海洋中各种形式的物质进行量化。特别是，海洋中生物和非生物颗粒的化学成分和大小分布对海洋生态系统有巨大影响，包括海洋食物链的动态、太阳能的垂直传输以及有机物和微量元素的运输。这些颗粒特征不仅影响而且反映了海洋中许多生物地球化学过程的变化。在这个项目中，一组科学家将推出一系列技术和数值建模创新，使他们能够通过对散射光的角度分布的光学观测来确定关键的生物地球化学数量。该项目将涉及一个跨学科的专家小组，他们将对海洋颗粒的光学进行理论建模，开发一种创新的高级数学建模方案，然后在实验室和现场测试和验证观察海洋颗粒特性的方法。一旦完善，这项技术应该会有更广泛的应用，因为它将被设计成能够在船载和自主平台上操作，并有可能在高时间和空间分辨率下提供颗粒尺寸分布和组成的估计。因此，它将使需要详细了解水生颗粒(生物地球化学、生物学、光学)的不同领域受益。该项目还将为研究生和本科生提供培训和支助，并进行公共教育宣传，包括特别努力接触北达科他州的美洲原住民。该项目的目标是从原位非显眼的体积散射函数测量中得出水柱定量颗粒大小和组成信息，以确定海洋生物地球化学颗粒种群的特征。粒子散射光的散射强度和偏振态的角度模式可以用4x4米勒矩阵(S)来描述，该矩阵本质上由粒子的大小、形状、组成和结构决定。因此，可以从S的测量中潜在地推断出粒子的性质。不幸的是，海洋水域的完整米勒矩阵很少被测量到。即使是最常见的测量成分，即表示非偏振光的角分布的体积散射函数(要素S11)，直到最近才被测量出来，随后开发了一种从VSF得出颗粒尺寸分布和组成的反演技术。最近，一种商用产品LISST-VSF可用于测量Mueller矩阵分量S11(VSF)、S12(线偏振)和S22(交叉偏振)，这可能提供了一种获得更详细的粒子表征的途径。该项目将利用散射建模的最新进展纳入S12和S22提供的更多信息，以进一步限制以下内容的反演：(I)使用S22(球形与非球形)更好地了解颗粒形状；(Ii)使用S11和S12减少不确定性；以及(Iii)进一步提高表征0.02至200um尺寸范围内颗粒的能力。这项研究将大大提高我们量化浮游植物细胞、碎屑颗粒、有机颗粒、矿物颗粒、气泡和乳化油(如果存在)等颗粒组的尺寸分布和折射率(与颗粒密度密切相关)的能力。

Understanding biogeochemical cycles and their interaction with the climate system requires quantifying the various forms of materials in the global ocean. In particular, the chemical composition and size distribution of living and non-living particles in the ocean have an enormous impact on marine ecosystems, including the dynamics of marine food chains, the vertical transmission of solar energy, and the transport of organic matter and trace elements. These particle characteristics not only affect but reflect changes in many biogeochemical processes in the ocean. In this project, a team of scientists will launch a set of technical and numerical modeling innovations that will allow them to determine key biogeochemical quantities from optical observations of the angular distribution of scattered light. The project will involve an interdisciplinary team of experts, who will theoretically model the optics of marine particles, develop an innovative advanced mathematical modeling scheme, and then laboratory- and field-test and validate the approach for observing marine particle properties. When perfected, the technique should see a broader application, as it will be designed to be amenable to operation on ship-borne and autonomous platforms with the potential to provide estimates of the particle size distribution and composition at high temporal and spatial resolutions. It should thus benefit different fields requiring detailed knowledge of aquatic particles (biogeochemistry, biology, optics). The project will also provide for the training and support of graduate and undergraduate students as well as public educational outreach, including a special effort to reach Native Americans in North Dakota.The goal of this project is to derive water-column quantitative particle size and composition information from in situ unobtrusive volume scattering function (VSF) measurements to characterize marine biogeochemical particulate stocks. The angular patterns of the scattered intensity and polarization state of the scattered light by particles can be described in terms of a 4x4 Mueller matrix (S) that is intrinsically determined by the sizes, shapes, composition, and structures of the particles. The particle properties can be, therefore, potentially inferred from measurements of S. Unfortunately, the complete Mueller matrix of oceanic waters has been seldom measured. Even the most commonly measured component, the volume scattering function (element S11) representing the angular distribution of unpolarized light, was scarcely measured until recently, followed by development of an inversion technique to derive size distributions and composition of particles from the VSF. Recently, a commercial product, LISST-VSF, became available for measuring the Mueller matrix components S11 (VSF), S12 (linear polarization), and S22 (cross-polarization), potentially providing an avenue to obtain a much more detailed characterization of particles. This project will incorporate the additional information provided by S12 and S22 using recent advances in scattering modeling to further constrain the inversion with the following: (i) better knowledge in particle shapes using S22 (spherical vs. non-spherical); (ii) reduced uncertainty using both S11 and S12; and (iii) further improved capability to characterize particles in the size range of 0.02 to 200 um. The study should greatly enhance our ability to quantify size distributions and refractive indices (closely linked to particle densities) for particle groups such as phytoplankton cells, detrital particles, organic particles, mineral particles, bubbles, and emulsified oil (if present).