Fractional Fourier transform-based detection and delay time estimation of moving target in strong reverberation environment

摘要

In ocean environments, reverberation is an inevitable interference for active sonar system. The reverberation has many characteristics quite similar to target echo, thus resulting in high false probability during active sonar detection. In this study, a novel method is proposed for both target detection and delay time estimation in environments experiencing strong reverberation. By utilising the focus characteristics of linear frequency modulated signal in fractional Fourier domain and Doppler shift of moving target, optimal transform angle of received signal is applied to detect targets based on fractional Fourier transform (FrFT). The authors have deduced a relationship among delay time, Doppler shift, and transform angle as the energy distribution in fraction Fourier domain is related with the delay time and Doppler shift of target echo. Simulation results have shown that the proposed method can achieve better performance with higher detection probability and lower root-mean-square errors in terms of delay time estimation under low signal-to-reverberation ratio environments as compared with match filter (MF). The experimental results have shown that multiple targets can be detected successfully. In addition, the accuracy of estimated delay time is even higher than MF in severe reverberant environment. It is pertinent to mention that reverberation may be suppressed by setting velocity threshold.