浅海多径时延估计的功率谱加权自相关方法

针对浅海近距离时倒谱多径时延峰变弱难以提取的问题,提出了一种功率谱加权自相关多径时延估计方法。该方法采用FFT估计信号功率谱,对功率谱取1-α次幂(0<α<1),再进行IFFT变换,对其实部进行峰值检测获得多径时延估计。根据目标能量通过特性在正横前递增正横后递减的特点,在已检测时延前后一定区间内搜索下一个时延值,实现多径时延的自动提取.理论分析表明,多径时延估计的倒谱法与自相关法都可以看作功率谱加权自相关法的特例.海试数据处理与基于Bellhop射线模型的仿真计算表明,该方法在近距离时多径时延峰比倒谱法更清晰,输出信噪比提高了3~4 dB.采用该方法自动提取的海底反射多径时延用于单个水听器对目标距离的估计,与GPS测量距离基本相符,验证了方法的有效性. 

Improving multipath time delay estimation in shallow water with power spectrum weighted auto-correlation

It's difficult for the cepstrum method to extract the multipath component of an underwater sound source at short range since the component becomes too weak. To deal with this problem, a power spectrum weighted auto- correlation multipath time delay estimation and its automatic extraction method is proposed. This method is carried out as follows:Firstly, the power spectrum of input signal is estimated with the FFT method; Secondly, the power spectrum is powered with 1-α (0 〈 α 〈 1); Thirdly, the IFFT is performed to transform the above data back to time domain. Lastly, a peak detection processing is performed to obtain the multipath time delay. When the preceding time delay is determined, the following time delay is searched within an interval around the preceding one. Theoretical analysis show that, the cepstrum and auto-correlation methods of multipath time delay estimation are two specifications of the power spectrum weighted auto-correlation method. By sea trial data processing and simulating with Bellhop ray model, the proposed method is proved to obtain stronger multipath trace than cepstrum method. Simulation also shows that the proposed method improves the output SNR of the multipath component by 3~4 dB. The bottom path time delay extracted with the proposed method is used in source range estimation with only a single hydrophone. The result is conformed basically to the range measured with GPS, which validated the effectiveness of our method.