Research on Active Sonar Object Echo Signal Enhancement Technology in the Spatial Fractional Fourier Domain

The detection and recognition of quiet, small objects in shallow water is one of the challenges in underwater acoustic signal processing, especially for buried objects. The seafloor strongly absorbs sound waves, while the object echo signals are weak, which makes the detection of the buried objects more difficult. Realizing object echo signal enhancement in a seafloor reverberation background and improving the signal-to-reverberation ratio (SRR) are critical problems. Based on the difference in energy aggregation between object echo signals and reverberation in the optimal fractional Fourier domain, a blind separation algorithm in the spatial fractional Fourier domain is presented. Expressions of the object rigid scattering components and the reverberation in the fractional Fourier domain are derived, and the energy distribution characteristics of both are analyzed. The objective function is constructed by the generalized correlation matrix of the multiple array signals in the optimal fractional Fourier domain, and the object rigid scattering components are obtained by approximate joint diagonalization. The simulation and data processing results show that the spatial fractional domain blind separation algorithm (FRFTBSS) can improve the signal-to-reverberation ratio. Compared with time–frequency domain blind separation (TFBSS), the proposed algorithm avoids the cross-item interference and performs better at lower SRR.