Direction of Arrival Estimation for Single Microelectromechanical Systems Vector Hydrophone Using Modified Wavelet Packet De-Noising

The complex and variable ocean environment introduces complex noise to the signal received by microelectromechanical systems (MEMSs) vector hydrophones, which seriously affects the target location. To improve the detection efficiency and broaden the application range of vector hydrophones, this article proposed a novel modified wavelet packet (WP) de-noising method, known as the WP energy (WPE) de-noising method. This method utilizes Shannon entropy to determine the optimal decomposition levels of WPs and calculates the energy of reconstructed signals in each frequency band to construct feature vectors. The WP with the larger energy is selected to reconstruct the signal until the root mean square error (RMSE) of the original signal and the reconstructed signal is minimized, thereby obtaining an optimal solution. The performance of this proposed method is evaluated through both indoor and outdoor experiments. The experimental results demonstrate that the developed method is effective in the direction of arrival (DOA) estimation of single-frequency signals and is feasible in low signal-to-noise ratio (SNR) situations. The method improves the azimuth discrimination ability of the minimum variance distortionless response (MVDR) algorithm, and DOA estimation errors are all within 1°. Furthermore, the indoor and outdoor experiments also demonstrate that the WPE de-noising method solves the group delay and distortion of signals caused by conventional filtering.