LAUSR

Tidal forcing in rivers and estuaries has a large impact on the use high-frequency acoustics for bathymetric mapping. Changes in the sound speed profile due to changing salinity and temperature conditions affect acoustic propagation, and bubbles, entrained in the tidal flow, cause high backscattering and attenuation. In this study, a forward-looking, high-frequency bathymetric sonar was used to observe estuarine dynamics near the mouth of the Connecticut River in June 2017. The sonar was deployed on a REMUS 600 AUV under the fresh water plume near the river mouth during flood tide, in the lower estuary during ebb tide and in the upper estuary during slack tide. Backscattering from subducted bubbles was observed which was dependent on the propagation path through the fresh or salt water. The bubble backscatter over a 200-m swath at the front of the fresh water plume allowed the structure of the plume to be observed from beneath the surface. These data are compared with other measurements on site, including...