Autonomous holographic imaging system for long term in situ studies of marine particle dynamics.

Florida Atlantic University, Boca Raton FL

Investigators

Abstract

A myriad of particles with vastly varying shapes and sizes, ranging from suspended organic/inorganic material to single celled, colonial, and multi-cellular plankton, densely populate the world's oceans. They are major drivers in fields as diverse as sediment transport, remote sensing/ocean optics, ecological studies of marine food webs, and carbon sequestration. Thus, instruments that can directly quantify particle characteristics, distribution, and concentration are critical to numerous science disciplines. Digital holography is an ideal tool to study particles, providing 3-D information within free stream sampling volumes that vastly exceed the 2-D cross sections sampled by conventional imaging instruments. Holographic images of undisturbed particles and their related flow fields can provide data critical to science questions requiring an understanding of particle motions and interactions, particle size, shape, fine-scale distribution, and spatial-temporal dynamics. The instrument being developed through this project could encourage interdisciplinary studies at the intersection of ocean optics, marine biology, biogeochemical cycles, and small-scale fluid dynamics, and lead to significant advancements in each of these areas. The objective of this project is to design, fabricate and rigorously test/validate an autonomous digital holographic camera system capable of quantifying the characteristics of in situ particles within a size range of ~ 1 micron to 2 cm. The instrument will be designed to sample an undisturbed volume of water and quantify particle number, size and shape (e.g. cross-sectional area, surface area, aspect ratio, sphericity), the 3-D spatial structure of the particle field (e.g. nearest neighbor distances), and the local fluid flows at the scale of the particles (via holographic PIV of the imaged volume). Identification of particles with unique shape characteristics (e.g. bubbles, oil droplets, phytoplankton and zooplankton) and particle orientation will be achievable. The instrument will be compact, submersible, biofouling resistant, fully autonomous with self-contained data logging and power, with adjustable resolution and sampling volume, and will be adaptable for use on vertical profilers, AUVs, tow-bodies, and long-term deployment on moorings. The device will be designed with the goal of science versatility and future commercialization for routine use by the scientific community.