Implementation and Testing of a Deepwater Correlation Velocity Sonar
Authors: Dickey V.R. , Bookheimer W.C. , Rhoades K.W. 
Published: October 2008

The paper describes a new sonar designated the Magnavox MX 810 Deep Water Correlation Sonar which is under development by the General Electric Company and the Magnavox Advanced Products and Systems Company. The sonar measures ship's velocity relative to the bottom but instead of using the conventional doppler effect, it uses the correlation method described by Dickey and. Edward in 1978 (Reference 1). In this method, the narrow beams required for doppler are not needed and a low frequency that penetrates to the bottom in deep water is used. The sonar was designed with the constraint that it use a transducer that mounts through a single 12 inch gate valve.

Most offshore geophysical surveys at present make use of an integrated navigation system with bottom referenced velocity input from a doppler sonar which, because of limitations on the sonar bottom tracking range, has difficulty in areas where the water depth is greater than about 500 meters. The MX 810 provides bottom tracking in regions of much greater water depth. It also may be applied as an aid in continuoos positioning of a vessel over a fixed location. It also should prove useful as a more general navigation aid.

The sonar is undergoing a series of tests using Magnavox's facilities for the purpose of verifying the performance and obtaining data to support and quantify planned improvements in both software and hardware. A prototype transducer of only 5 watts power output was used, but in spite of this low power, successful operation to depths of 1900 meters was obtained. Extrapolation to system parameters to be implemented in production models predicts operation to depths of 5000 meters.

INTRODUCTION

The Magnavox MX 810 Deep Water Correlation Sonar has been designed to provide a true earth referenced velocity input to an integrated navigation or positioning system in water depths that far exceed the maximum bottom-tracking range of conventional doppler sonar. The development of this sonar is being carried out by the General Electric Company and the Magnavox Advanced Products and Systems Company. The prototype is physically designed so that the transducer is readily mounted through a 12" gate valve. The sonar system has been operated successfully aboard the Magnavox research vessel, Duchess Diane, in depths up to 1900 meters, this being the deepest water conveniently available. This paper will describe the prototype, discuss the theory of operation, the first sea tests and their results, and identify the planned refinements which should permit operation in depths to 5000 meters, with accuracy of better than 0.496 of distance traveled.

COMPARISON OF CORRELATION AND DOPPLER METHODS

In a conventional doppler sonar, ship's velocity is determined by estimating the doppler frequency shift of sound waves scattered from the bottom. In order to obtain sufficient accuracy when the frequency measurements are translated into ship's velocity, the waves must be confined to several narrow beams. This usually requires the use of a frequency that is too high to propagate readily to the bottom and back in deep water.