The influence of correlation delay and spectral asymmetry on acoustic Doppler velocimetry bias

The influence of correlation delay and spectral amplitude asymmetry of the received signal on acoustic Doppler velocimetry bias with the complex covariance approach are studied.Neglect the simplifying error of the velocimetry formula,the velocimetry bias is simplified to the Doppler shift measurement bias.It is deduced that if not considering the beam angle,the narrowband frequency measurement is unbiased while the broadband frequency measurement is biased;and if considering the beam angle,the narrowband and broadband frequency measurement are all biased.Inaccurate correlation delay and asymmetric spectrum are important sources of the biases.Simulation analysis shows that the frequency measurement bias can be reduced to 0 by eliminating the correlation delay inaccuracy or spectral asymmetry.Based on the above findings,the ellipse grid frequency measurement model with dual weighting of signal phase and amplitude for the bottom tracking Doppler velocimetry sonar is proposed;the theoretical analysis for the difference between the broadband and narrowband frequency measurement bias with the same pulse length is given.The proposed broadband frequency measurement model is utilized to simulate the fitting curve of the Doppler shift and the frequency estimation bias,with which the actual data is corrected.In the water tank experiment,the relative velocimetry bias decreases from 1.14% to 0.78%,and the maximum absolute value decreases from 2.83 relative velocimetry bias decreases from 4.79% to 3.82%.