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This paper presents a study of the effects of compass bias on navigational accuracy of autonomous underwater vehicles. Low cost vehicle systems utilize a magnetometer, and Doppler sonar for dead reckoning, and a DGPS fix when surfaced. By learning the compass bias from a few DGPS fixes, the navigational errors can be bounded with only a small number of fixes. The study is conducted using the Florida Atlantic University OEX vehicle and a large set of data obtained from a 3.5 Km run including several segments at different headings so that the dependency of compass error on actual heading could be evaluated.

Abstract-This paper provides an overview of the Naval Postgraduate School ARIES autonomous underwater vehicle. An attempt is made to highlight its' current operational capabilities and provide a description of future enhancements for greater mission utility and flexibility. An overview of the vehicle design along with descriptions of all major hardware components and sensors is given. A major discussion of the implementation of a modular, multi-rate, multi-process software architecture for the ARIES is provided. The architecture is designed to operate using a single computer processor or two independent, cooperating processors linked through a network interface for improved load balancing. A dual computer implementation is presented here since each processor assumes different tasks for mission operation. Also included is a section on the underwater navigation method used. It involves the use of a real-time extended Kalman filter that fuses all sensor data and computes the real time position, orientation, velocity, etc., of the vehicle. Issues of navigational accuracy of the filter are also discussed. The work concludes with a discussion of using the ARIES as a communications server in a multi-vehicle environment. It is proposed to use the ARIES as a mobile communications relay between a command and control station on the surface and multiple vehicles operating below. The advantages of using a mobile relay over fixed buoys are discussed.

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