Optical depolarization from turbulent convective flow: A laboratory study

In an effort to investigate the role of turbulence in near-forward scattering, laboratory measurements of scattering on turbulent flow were carried out in a Rayleigh-Benard convective tank. Particle Image Velocimetry and profiling thermistor temperature measurements are used to characterize the turbulent flow through determination of the large scale flow features, turbulent kinetic energy dissipation rates, and thermal dissipation rates. Polarized diffractometer measurements allow for determination of the turbulence-induced depolarization rate, which is comparable to that observed with polarimetric lidar. Measurements were made over a range of turbulent strengths, with Rayleigh number between 108 and 3*109, and with turbulent parameters corresponding to those characteristic of the oceanic mixed layer. Results show that the turbulence-induced depolarization rate is indirectly proportional to the strength of the turbulent flow, suggesting that light beam depolarization from turbulent flow may contain useful information regarding the smallest length scales of turbulent flow.