EO observations of currents and turbulence via mixing of sediment load variations

Airborne time series imagery is used to measure frequency-wavenumber spectra of gravity waves, accurately locating the dispersion surface to retrieve water depths and currents. In shallow water, the same frequency-wavenumber spectra often exhibit an ‘advective surface’ caused by flow-induced transport of sediment variations indicative of partly mixed water masses having different sediment loads. The orientation of this spectral surface provides the ‘mean’ current associated with this advection and this value agrees, to within a few percent, with the gravity wave Doppler when both wave and advective signatures are present. This paper describes our attempt to use these same image data to measure the turbulent velocities associated with flows in moderately shallow water found in the near-shore ocean and estuaries. We present examples of turbulent eddy features and demonstrate that the image data are consistent with a Kolmogorov inertial range cascade. We have attempted to measure the short wavelength (<30 m), smaller magnitude current variations in these flows by two separate methods, although we have not been successful in unambiguously quantifying them to date. Our experimental data do, however, provide us with a clear idea of the precision that is necessary to accomplish this in our space-time image data.