Polarimetric lidar measurements of aquatic turbulence - laboratory experiment

Lidar is one of few remote sensing methods available to researchers to sense below the oceanic air-surface. We present polarimetric lidar measurements of turbulence in a laboratory generated turbulent flow. We found that the nearforward light depolarization characterized by the depolarization rate γ(z), varies with the turbulent flow parameter: χ(z)∊(z) 1/4 , where χ(z) and ∊(z) are the respective depth dependent, temperature variance, and turbulent kinetic energy dissipation rates. The presence of particles in the flow modifies the values of γ in such a way that the ratio γ(z)/α(z) becomes independent of the particle concentration and depends only on χ(z)∊(z) 1/4 . We posit that the mechanism of light depolarization in turbulent flow with particles is forward scattered light interaction between turbulent refractive index inhomogeneities and flow particles. Such interactions result so that the observed depolarization rate, γ(z), is much larger than expected from 'pure' turbulent flow. Our observations open up the fascinating possibility of using lidar for turbulence measurements of aquatic flows.