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

Stanford University, Stanford CA

Investigators

Abstract

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.