Abstract
Inhomogeneities in the refractive index induced by temperature fluctuations in turbulent flows have the effect of scattering light in near-forward angles. We have developed a method that extracts the rate of Temperature Variance Dissipation (TVD) and its spectrum from the properties of light scattering and have built an instrument - Optical Turbulence Sensor (OTS) - that implements the method. OTS uses a linear wavefront sensing Hartmann array and allows for nearly instantaneous measurements of temperature variance in turbulent flows. The instrument has been tested in an situ experiment carried out from a drifting vessel at a site off the coast of Newport, Oregon. Here we compare the temperature variance measured by OTS and its spectra with both theoretical predictions and with spectra obtained from a fast thermistor sensor.
Highlights
The fluxes of heat, salt, nutrients, oxygen, etc. are of primary importance in applications as diverse as modeling of ocean circulation, primary productivity, pollutant dispersal, particle and sediment transport
We have developed a method that extracts the rate of Temperature Variance Dissipation (TVD) and its spectrum from the properties of light scattering and have built an instrument - Optical Turbulence Sensor (OTS) - that implements the method
Estimates of turbulent fluxes in the ocean are obtained from assumed relations between these fluxes and the rates of turbulent kinetic energy dissipation (TKED) and of temperature variance dissipation (TVD)
Summary
The fluxes of heat, salt, nutrients, oxygen, etc. are of primary importance in applications as diverse as modeling of ocean circulation, primary productivity, pollutant dispersal, particle and sediment transport. For some time [2], the optical oceanography community has theoretically postulated the effect of turbulence on light propagation in the ocean. Experimental oceanic studies of the interaction between light and turbulence have been rare, in large part due to the complexity of appropriate experiments and to the difficulty of making angular measurements of scattered light at small angles in the presence of the unscattered light beam. Recent laboratory measurements of near-forward scattering (range of 10 −7 to 10−3 rad) of the light beam on turbulent flow show that under energetic oceanographic conditions, the total scattering coefficient can be larger than that of particulates and that the turbulent inhomogeneities of fluid flow have the effect of scattering light in near-forward angles, providing an opportunity to use optics to quantify turbulence [4]. Combining the optical measurement with appropriate processing allows nearly instantaneous estimation of spectra of temperature variance and of the rates of temperature variance dissipation
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