Strapdown heading sensor for towed arrays

Hydrophone arrays for locating acoustic noise sources in marine environments are often towed rather than platform mounted so that the arrays can be longer and hence better angular resolution can be obtained. However, the array shape and pointing direction, required for accurate location of the acoustic source, can vary considerably, particularly when the towing platform is manoeuvring, thus degrading the array performance. To overcome this problem, heading sensors may be incorporated at intervals along the array. Each sensor then measures the pointing direction of a particular section, thus enabling the array shape to be determined. Desirable properties of such a heading sensor include small size and low power consumption in addition to reliability and accuracy in measuring its orientation. The authors describe an implementation of a strapdown heading sensor based upon three nominally orthogonal accelerometers and three Hall effect magnetometers, also nominally orthogonal