The effect of sound velocity errors on multi-beam sonar depth accuracy

A number of hydrographic organizations and commercial operators are using multi-beam sonar systems for mapping shallow and deep water areas. With transducer motion and refraction playing an important role in measurement accuracy, errors in ship motion data and sound velocity profile information are major contributors to inaccuracies in the measured depth. The effect of errors in sound velocity is examined is shown to be different for flat-level transducers and for tilted transducers or those with sector steering. On survey vessels where roll is significant, the roll can modulate the depth errors contributed by sound velocity uncertainty. These errors are discussed in relation to the IHO standards for surveys, and methods of error control are suggested.