Progress on the use of autonomous underwater vehicles to study estuaries

Abstract

Estuaries are a challenging environment to use acoustically navigated Autonomous Underwater Vehicles (AUVs) due to highly variable currents, relatively shallow and variable bathymetry, large buoyancy changes, suspended sediments, marine biota, and bubble plumes. The benefit to using AUVs is their ability to perform repeat automated surveys and targeted sampling of features using either remote control or on-board redirects. Our REMUS 100 AUVs are equipped with up/down looking ADCPs, CTDs, and optical backscatter sensors. Our AUVs use Long Base Line (LBL) underwater navigation, with up to four transponders, and were recently equipped to carry broadband hydrophones. We will share our experience operating these AUVs in several estuaries to characterize variability in optical and acoustical backscatter associated with estuarine features of interest (fronts, river plume, and the salt-wedge). We will discuss how these features negatively impact AUV sampling via, for example, degraded underwater communications and bottom tracking. We will also present some examples of concurrent sampling by AUVs and an advanced sonar (static and mobile) demonstrating the potential use of AUVs in estuarine research for 4D visualization of estuarine features of interest. [This work was supported by Office of Naval Research.]