Velocity accuracy and performance characteristics of Janus acoustic Doppler navigator systems

Abstract

The Janus radar Doppler navigator system has excellent velocity measuring accuracy which the analog underwater acoustic navigator system, using dual independent bottom and volume reverberation modes, cannot match. While considerable differences exist between aerospace and hydrospace vehicle dynamics, they can be largely mitigated using only millisecond delays in post time integration smoothing of the velocity-time history which results in small dynamic induced system errors. The transducer construction and installation errors are primarily random, small, and partially reducible in proportion to time and cost. The basic difference between the radar and acoustic system velocity accuracy is in the water reverberation mode which is necessary for the latter system in deep water. This error depends on ocean currents, upwelling, internal waves, etc., but most importantly on the water particle motion caused by the displacement of water as the hull moves. This paper is a review of the Janus acoustic system and the various intrinsic errors, including calculations of the limiting error due to water undergoing essentially incompressible flow around an ellipsoidal model of a submarine hull.