Characteristics of an autonomous underwater vehicle with a towed hydrophone array

Abstract

This paper presents the performance results of a REMUS AUV, a proven low noise vehicle with precise navigation, that was modified by the addition of a prototype towed hydrophone array. A quiet, acoustically sensitive synthetic aperture sonar at low frequencies required a 10 m long acoustic section of the array separated from the vehicle with a 10 m long tow cable. A drogue was used to produce an initial drag and to minimize motions at the end of the array. REMUS was designed to carry a wide variety of sensors but, the 10 meter towed array presented many challenges. Unlike vehicles with thrust vectoring, REMUS requires forward motion using three axis control to maintain constant depth without the added drag of fin control. In light of this, several hardware and software adjustments were required to ensure successful long-range missions with the system. The vehicle adjustments, along with the results from at-sea engineering trials of the vehicle-array system are presented and demonstrate the ability of the system to maintain a constant depth with a stable array tow. Effects of the added drag on the vehicle were evident in the on board recorded data, which enabled the adjustment of vehicle control through software and mechanical considerations such as attachment point of the array to the vehicle. Rapid improvement in vehicle performance in between missions was achieved on board the support ship as a direct result of the ability to view and interpret mission data in the field. Based on the engineering trials with this vehicle array system, estimates of the vehicle and array system performance including power requirements, diving capability, turning capability, effects of currents, and navigational errors are discussed