Sediment Dynamics in the Energetic Nearshore Zone: Acoustic Remote Sensing and Model Validation

Abstract

Acoustic backscatter data were collected in the shallow nearshore environment under breaking and non-breaking waves, using a multi-frequency sonar at 0.5, 1.0, and 2.0 MHz. The data are used to develop and test an acoustic inverse model for measuring suspended sediment concentration (SSC) in the presence of bubbles generated by breaking waves. The model leverages the contrasting frequency dependence of acoustic scattering by bubbles and sand, to simultaneously estimate SSC and bubble void fraction. Validation against in situ sediment measurements shows the acoustic technique can recover sediment concentration with good accuracy in both breaking and non-breaking waves, unlike existing algorithms which only perform well in non-breaking waves. Finally, data from the experiment are used to validate existing theories for suspended sediment dynamics under breaking waves, for which few previous data sets exist.