浅海双基地有源探测调频信号直达波消除

Direct blast cancelling of the frequency modulation signals for bistatic active sonar in shallow water

双基地有源探测常采用长脉宽探测信号以获取更高的时间增益,容易导致回波弱信号被强直达波信号掩蔽而影响回波检测。针对长调频信号直达波的干扰,提出基于分数阶傅里叶变换(FrFT)的直达波消除方法。该方法利用调频信号在时频分布上的稀疏性,通过对接收信号进行分数阶傅里叶变换分离直达波和回波信号然后在变换域对直达波信号进行去除。远程双基地有源探测的收发距离较远,直达波信号经过长距离传播,浅海多途信道的影响不可忽视,因此通过数值仿真分析了浅海声传播对FrFT消除直达波方法的影响。理论和仿真分析结果表明,FrFT对一定时频分布的调频类信号具有足够的分辨力,可以有效在浅海环境中分离和消除直达波干扰。利用2018年的一次海上试验数据,对基于FrFT的直达波消除方法进行了检验,结果表明该方法可有效消除有源探测中的直达波干扰。该方法计算复杂度低,受浅海频散信道影响小,具有很好的稳健性。

For getting high processing gain,the bistatic active detection often use long-duration probing signals with the compromise of losing more weak echoes in strong blast.A method based on the Fractional Fourier Transform(FrFT)is proposed to diminish the direct blast of Frequency Modulation(FM)signals.With the sparse representation of the frequency modulation signals in the time-frequency domain,the direct blast and the echoes can be easily separated.The influence of multi-path can not be ignored because the distance from transmitter to receiver is long.Therefore,the influence of acoustic propagation in shallow water is analyzed by numerical simulation.Theoretical and simulation analysis show that the resolution of FRFT is high enough for FM signals with certain time-frequency distribution and the corresponding direct blast can be effectively separated and diminished.The proposed method is applied to the real active sonar data collected during the South China Sea experiment in April 2018.The experimental results indicate that the direct blast can be diminished excellently.Furthermore,the proposed method is stable in a shallow water environment and with low computational complexity.