A Shallow Water Acoustic Network for Mine Countermeasures Operations with Autonomous Underwater Vehicles
Abstract -
Autonomous Underwater Vehicles (AUVs) are an alternative to traditional mine countermeasures (MCM) operations using divers or marine mammals. REMUS AUVs can be deployed at a distance and map an area using side-scan sonar, then identify and classify bottom targets using on-board processing. A shallow water acoustic communications network has been implemented to enable cooperative MCM operations with REMUS AUVs. The network provides connectivity between an operator and multiple REMUS vehicles and also allows vehicles to exchange information. This paper describes the MCM vehicle network and the acoustic network infrastructure. Results are also presented from recent demonstrations where REMUS vehicles mapped an area and detected and classified bottom objects while being monitored and controlled by a remote operator.
I. INTRODUCTION
The REMUS AUV was originally developed for scientific sampling applications in water up to 100 m depth [1]. After the first vehicles were built and demonstrated for civilian applications, the Navy expressed interest in equipping them with side-scan sonar and using them to map the bottom and find mines in coastal environments. As a result, WHOI built and operated several versions of the REMUS AUV, including Advanced Development Model (ADM) and Engineering Development Model (EDM) systems prior to performing a technology transfer for commercial production [2] [3].
Prior to commercialization WHOI began working to install acoustic communications systems in REMUS vehicles as part of the Office of Naval Research Very Shallow Water and the Surf Zone Mine Countermeasure program (VSW/SZ MCM). The first modem integrated into the vehicle was the WHOI Utility Acoustic Modem (UAM), operating at 15 kHz [4]. However, the UAM is relatively large for a small AUV and used payload space that was needed for additional sensors and processors. Thus the Micro-Modem, a very compact (1.75 by 7.5 in) modem developed during the MCM program was integrated as part of a pre-planned product improvement (P3I) program. During the program the communications frequency was increased so that it is compatible with the on-board acoustic navigation system and an interface designed so that it can share the navigation transducer and power amplifier. The result is a highly integrated system that requires only the Micro-Modem DSP card, which is just 1.75 by 4.5 inches.
From the start the VSW/SZ MCM program included multiple vehicles navigating and communicating in the same area (Fig. 1). Thus the initial system design included time-division multiple-access (TDMA) networking with centralized control to allocate cycles to different vehicles for communications or long baseline navigation [5]. As the system has been developed and demonstrated its capabilities have continued to evolve.
The paper includes a description of the entire system, along with test results from recent exercises. The paper is organized as follows. Section II describes the communications system using the ISO 7-layer model as a guide. In Section III the operational platforms are described, and in Section IV demonstrations are described and results are presented.

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