Performance of a Two-Hydrophone Heading Sensor and AUV Formation Flying Controller

Abstract : De-centralized formation control is one way to enable the function of multiple Autonomous Underwater Vehicles (AUVs). It is thought that decentralization can lower the requirements on communication for control, and formation-flying would simplify the oversight of large numbers of vehicles operating simultaneously. In this paper, we describe an algorithm that would enable multiple vehicles to maintain formation. Follower vehicles are equipped with a sensor that can determine a relative angular heading to the source of an intercepted acoustic signal from a leader vehicle. This sensor consists of two hydrophones separated by a fixed distance on the follower vehicles. Experiments were conducted to assess the ability of the two-hydrophone sensor to determine bearing angle in the presence of propeller noise, relative motion with consequent Doppler shift, and a test application in a formation-flying scenario. The effect of using cross-correlation and matched filter signal processing procedures for determination of bearing angle were also compared. It was found that the two-hydrophone sensor could determine bearing angle in the presence of propeller noise, over distances ranging from 9-400m considered in the experiments to an accuracy of approximately 4o. Higher accuracy in bearing angle determination was obtained with matched filter than with cross-correlation signal processing, in spite of relative motion.