Acoustical remote sensing of energy dissipation using scintillation analysis

Abstract

Forward-scattered sound propagating through turbulent fluids produces characteristic scintillation patterns which have been interpreted in terms of refractive index fine structure and mean transverse motion of the flows under study. Reciprocal travel-time measurements yield information about velocity variability along the acoustic path. By combining these two types of measurements, the contributions of sound speed and velocity fluctuations to forward acoustic scatter can be separated. These techniques are illustrated using measurements outlined in the boundary layer under ice in the Arctic. Under the assumptions of a Kolmogorov inertial subrange and Taylor's frozen field hypothesis, reciprocal travel-time measurements provide estimates of turbulent kinetic energy dissipation rate averaged over the propagation paths. Sound speed variability is negligible in the Arctic boundary layer; for this reason, acoustic scintillation analysis also yields estimates of energy dissipation rate which compare well with those obtained from reciprocal travel-time measurements.<>