Improvement of Underwater Laser Ranging Accuracy Based on Wavelet Time-Frequency Analysis

A laser time-frequency analysis ranging method based on wavelet transform for underwater target detection has been proposed in this paper. The band-pass filtering characteristics of the wavelet transform are combined with the energy conservation of the signal time-frequency domain during the wavelet time-frequency decomposition process of the echo signal. Binary spline interpolation is used to obtain the time-frequency correspondence matrix of the echo signal energy. In this method, the frequency range of the target echo signal is selected through the multi-layer wavelet time-domain decomposition process. The time-frequency energy matrix of the echo signal is extracted in the frequency range, and these frequencies are integrated to determine the restored time-domain echo signal. The corresponding delay of the target is determined by the peak detection method, and the target distance information is retrieved. The emission source is a 532 nm pulsed laser with a repetition frequency of 50 kHz, a pulse width of 1 ns, and average power of 3 W. The APD detector and the acquisition system with a bandwidth of 1 G are used to receive the echo signal. By detecting diffuse reflection targets in the water with an attenuation length of 10, the signal processing method can reduce the ranging error from 11.83 cm to less than 4 cm.