Theory and signal processing of acoustic correlation techniques for current velocity measurement

The theoretical model and signal processing of correlation measurements to estimate current velocity are discussed. The sonar space-time correlation function of volume reverberations within Fraunhofer zone is derived. The function, which is the theoretical model of acoustic correlation measurements, is in exponential forms. The characteristics of the correlation values around the maximum of the amplitude of the correlation function, where most information about current velocity is contained, are primarily analyzed. Localized least mean squares (LLMS) criterion is put forward for velocity estimation. Sequential quadratic programming (SQP) method is adopted as the optimization method. So the systematic signal processing method of acoustic correlation for current velocity measurements is established. A prototype acoustic correlation current profiler (ACCP) underwent several sea trials, the results show that theoretical model approximately coincides with experimental data. Current profiles including the speed and direction from ACCP are compared with those from acoustic Doppler current profiler (ADCP). The current profiles by both instruments agree reasonably well. Also, the standard deviation of velocity measurement by ACCP is statistically calculated and it is a little larger than predicted value.