浅海低频声场中目标深度分类方法研究

分析了浅海甚低频声场中的垂直双水听器的互谱特性，尤其关注了声场中只存在两阶简正波时声压互谱的有功分量.数值计算表明：当两个水听器的深度布放合理时，声压互谱有功分量的正负号分布与水平距离无关，选择合适的水听器深度布放组合，可以用于水面目标、水下目标的双择判决；声速分布对该方法的使用影响不大，海底存在吸收将影响算法的作用距离，但在有效作用距离内，该算法仍有较好的稳健性.运用Pekeris波导有效深度的概念建立了声压互谱有功分量正负号分布特性的近似理论分析并可预报双水听器合理的布放深度.理论分析揭示了双水听器布放深度之和应等于波导有效深度，并且在有效深度限制的波导范围内，整个声场的声压互谱有功分量的正负号分布被分为三个水平区域.理论分析加深了对浅海低频声场特性的理解，对该算法的实际使用有指导意义.关键词：目标深度分类浅海低频声场声压互谱有功分量

Research on target depth classification in low frequency acoustic field of shallow water

The cross-spectrum characteristics of sound pressure between two hydrophones deployed vertically are analyzed in low frequency acoustic field of shallow water, more attentions are paid to the cross-spectrum active component of sound pressure when only two normal modes are trapped in the waveguide. The numerical results show that （1） the sign of the sound pressure cross-spectrum active component is independent of range when receiving transducers placed in appropriate depths, so it can be used to tell whether the sound source is near the surface or underwater by selecting a pair of appropriate deploying depth of transducers; （2） acoustic velocity profiles have little effects on the application of this method, the seabed attenuation will limit the detection range, but the algorithm still has a good robustness in the valid detection range. Approximate theoretic analysis of cross-spectrum active component characteristics is proposed in the paper combined with the concept of effective depth, and the prediction formula of appropriate deploying depth of transducers is presented. The theoretic analysis indicates that the sum of the bi-hydrophone depths should be equal to the waveguide effective depth and the sign distribution of the sound pressure cross-spectrum active component is divided into three level regions in an ideal pressure-release waveguide. The theoretic analysis provides deeper understanding of the low-frequency sound field characteristics in shallow water and also guidance to the application of the algorithm.