Collaborative Research Proposal: Development of a Combined In Situ Particle Imaging Velocimeter / Fluorescence Imaging System

Stanford University, Stanford CA

Investigators

Abstract

The PIs propose to build a new system that will image multiple wavelengths of fluoresced and scattered light and perform stereo particle image velocimetry (3D PIV) measurements. These data will enable maps of fluid flow and derived quantities such as strain rate, vorticity, and the dissipation rate of turbulent kinetic energy to be produced. Measurements will be made on identical scales (20 x 20 x 0.6 cm with 100 um resolution), nearly simultaneously, allowing in situ 3D mapping of biological distributions to microscale physical flows. It is proposed that the multiple imaging wavelengths will allow a degree of taxonomic discrimination among fluorescent particles, while the side-scattered light will provide images of all particles that scatter the excitation irradiance including most of the phytoplankton appearing in the fluorescence images, as well as zooplankton. The 3D PIV-multispectral imaging fluorometer will be mounted on a free-falling platform with a suite of auxiliary instruments and a water sampler for image ground-truthing that has already been constructed and shown to provide undisturbed views of plankton in the water column. Images will be captured in a plane extending below the platform to obtain distributions unaffected by the platform. Shipboard epifluorescence microscopy will be used to identify dominant organisms in the images. Relating microscale distributions of plankton to microscale physical dynamics in the ocean has been largely limited by a lack of technology. The combination of multiple-wavelength imaging and PIV will allow in situ investigations of fluorescent particle/bulk fluorescence relationships, microscale distributions of plankton in relation to microscale flows, spatial relationships of grazers and primary producers, and physical mechanisms underlying fine- and microscale biological patchiness. This instrument is an enhancement of an existing 2D imaging fluorometer developed by the PIs that has only one sensing wavelength, and does not gather simultaneous physical data on the same scales as the fluorescence images.