Development and Validation of an In-Situ Particle Tracking Velocimetry System for Ocean Turbulence Measurement

海洋流动的大尺度模型需要小尺度过程的模型，比如驱动混合的湍流。然而，我们对这一过程的理解是高度不确定的，特别是在像海洋这样的密度分层介质中。试图使用现有的海洋学仪器测量相关的湍流量需要对这些小规模流动做出假设，而这些假设可能并不总是有效的。该项目将通过开发和验证一种新的光学仪器来弥补这一差距，该仪器能够在相关的现实环境中测量湍流海洋流动的完整小尺度细节。通过将实验室流体流动研究开发的测量工具应用于现场，该项目将有助于使现场测量能力更接近最先进的实验室诊断能力。小规模湍流波动对密度场的搅动是驱动海洋混合的基本过程，因此是海洋模式的关键要素。诸如耗散率之类的量对于参数化混合是必不可少的，但如果不使用传统仪器进行假设，则无法测量。分层湍流的理论研究也受到限制，考虑的是哪些量是可测量的，而不是哪些是最重要的。该项目将通过开发和验证3D粒子跟踪测速（PTV）系统来解决这两个问题，该系统能够对海洋分层湍流的全微尺度结构进行现场测量。与之前基于水下图像的测量工具不同，该系统将能够在三维体（而不是平面）中解析速度场的所有三个分量，具有足够的分辨率直接测量瞬时速度梯度的所有分量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Large-scale models of ocean flows require models of small-scale processes such as the turbulence that drive mixing. However, our understanding of such processes is highly uncertain, particularly in a density-stratified medium like the ocean. Attempting to measure the relevant turbulence quantities using existing oceanographic instrumentation requires making assumptions about these small-scale flows that may not always be valid. This project will bridge this gap by developing and validating a new optical instrument that is capable of measuring the complete small-scale details of turbulent ocean flows in relevant real-world settings. By adapting measurement tools developed for laboratory fluid flow studies for use in the field, this project will help to bring field measurement capabilities closer to what is possible with state-of-the-art laboratory diagnostics. Stirring of the density field by small-scale turbulent fluctuations is the fundamental process driving mixing in the ocean, and is thus a key element of ocean models. Quantities such as the dissipation rate are essential for parameterizing mixing, but cannot be measured without assumptions using traditional instruments. Theoretical investigations of stratified turbulence have also been limited by considerations of which quantities are measurable rather than which are most important. This project will address both of these gaps by developing and validating a 3D particle tracking velocimetry (PTV) system capable of making in-situ measurements of the full microscale structure of stratified turbulence in the ocean. Unlike previous submersible image-based measurement tools, this system will be capable of resolving all three components of the velocity field in a 3D volume rather than a plane, with sufficient resolution to measure all components of the instantaneous velocity gradient directly.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.