The impact of acoustic oceanographic methods on estuarine dynamics research

Abstract

Estuaries present unique challenges for observational oceanographers, due to their intense spatial gradients and unrelenting temporal variability. The influence of spatial and temporal variation of estuarine structure and flow on the time-averaged regime is the most important research problem in estuarine physical oceanography. Acoustic methods have played an essential role in revealing this spatial and temporal variability, and new advances in acoustic methods are continuing to provide the most important advances in observations of estuarine processes. The measurement of acoustic backscatter has been a mainstay of estuarine physical oceanography, first for providing qualitative images of the density structure, then for quantifying suspended sediment distributions, and most recently for quantifying the intensity of stratified turbulence. Improved resolution of new systems is revealing the internal structure of shear instability and the mechanics of the transition to turbulence. Acoustic Doppler techniques are so routine now as to be taken for granted, but their impact on the field cannot be overstated, and the new advances in pulse-coherent velocity profiling are continuing this revolution in acoustical oceanography. Acoustic propagation in estuaries has not yet received much attention, but its importance to the operation of autonomous vehicles and long-term monitoring should bring this challenging acoustics problem to the forefront.