Accurate prediction of signal waveform in the convergence zone of the South China Sea based on frequency shift compensation

Abstract

In a deep-sea environment in the South China Sea, a towed sound source is near the surface, and the acoustic signal is received by the vertical array of submersible buoys. The correlation values between the predicted and the measured signal waveform of the first two convergence zones (CZs) are poor, both below 0.5. The sea condition of the test area is good, the hydrological environment changes little in the horizontal direction. The analysis shows that when the underwater acoustic waveform is predicted, due to the relative motion of the transmitting and receiving elements, the channel dispersion caused by the Doppler effect leads to signal distortion. Therefore, the sampling frequency is broadened by 0.125 times to both ends, and the frequency shift corresponding to the maximum value of the waveform correlation peak is used as the optimal compensation for Doppler frequency offset. The results calculated by the RAM model show that the predicted and measured signal waveforms are in good agreement, and the correlation degree is significantly improved. Among them, the average normalized correlation values of the measured and predicted waveforms at different receiving depths in the first and second CZs are 0.84 and 0.82, respectively.