多途浅水环境水下散射体声场扰动层析成像方法与试验研究

The technology of underwater acoustic barrier is an important research direction in the underwater security areas. The main principle of this technology is to detect hidden underwater invading targets such as divers and UUV by detecting perturbation signals generated by its forward scattering. The main technical difficulty of underwater acoustic barrier is that the perturbation signals and the signals of acoustic incident wave arrive at the receiver simultaneously, so that it is infeasible to estimate the ranges and depths of underwater targets through methods based on the time difference. Tomography imaging in shallow water environment is put forward to deal with this problem, however, current research works are mainly based on Born approximation of the acoustic Helmholtz equation, which only suit for weak scattering situation, that is ka<<1. The issue of this projects are mainly focus on the following three aspects. Firstly, the numerical model for forward scattering calculation of underwater targets is developing at the conditions that ka>>1 and multipath environments. Secondly, the inversion theory and method of local impedance changes in shallow water environments produced by underwater targets is developing. Thirdly, experimental research on tomography imaging of acoustic field perturbation from underwater targets in multipath shallow water environments is also carrying out. The results of our project will provide an effective method to locate underwater targets and distinguish multiple targets, and will promote the developing of the technology of underwater acoustic barrier.

水下声栅栏探测技术是水下区域安防领域的重要研究方向，其原理是通过检测水下目标前向散射现象产生的扰动信号来监测水下隐蔽侵入的蛙人、水下无人航行器目标等。声栅栏探测的主要技术难点是水下目标的声场扰动信号和入射声波信号同时到达接收端，难以通过建立在时延基础上的测距和测深方法估计目标的水下位置。浅水环境声层析是尝试解决该问题的方法之一，现有研究是建立在声学Helmholtz方程的Born近似基础上，仅适用于弱散射(ka<<1)情况。本项目的研究内容包括：建立非弱散射(ka>>1)和多途条件下目标前向散射声场数值模型，采用非线性优化方法建立水下目标产生的局部水体阻抗变化的反演方法，并进行湖上水中目标声场扰动层析成像验证试验。本项目研究成果给出利用水下目标声场扰动信号进行目标测距、测深和多目标分辨的一种实现途径，为声栅栏探测技术的进一步发展提供技术支撑。

声栅栏探测技术是水下安防领域的研究方向之一，其原理是通过检测水下目标前向散射产生的扰动信号来监测水下隐蔽侵入的蛙人、水下无人航行器等目标等。声栅栏探测的主要技术难点是水下目标的声场扰动信号和入射声波信号同时到达接收端，难以通过建立在时延基础上的测距和测深方法估计目标的水下位置。.本项目针对水下目标声层析成像问题开展了信号处理算法研究，主要工作总结如下：首先，针对水下小目标声场扰动信号建模问题，建立了水下规则几何体目标前向散射声场及总声场的简正级数模型、基于吸收边界层(PML)的水下小目标散射声场的轴对称有限元计算模型。其次，针对水下散射体声场扰动层析成像信号处理问题，在小于20kHz的水声频段，建立了基于傅里叶衍射定理的波数域成像方法和时域滤波反传播层析成像方法，开展了前向散射型水声层析成像仿真研究；在100kHz—200kHz水声频段，建立了基于傅里叶切片定理层析成像方法，开展了反向散射型水声层析成像仿真研究。再次，针对前向散射型水声层析成像和反射散射型水声层析成像试验验证问题，构建了利用两个直线滑台的水下刚性球体目标直达声场扰动信号自动测试系统，开展了利用目标前向散射信号的水下刚性球体水声层析成像信号处理方法试验验证研究，结果表明通过声场扰动层析成像可以反演水下散射体的位置；构建了利用转台的水下复杂外形小目标回波测试系统，开展了利用目标反射散射信号的水中复杂外形小目标水声层析成像试验。本项目研究成果给出利用水下目标声场扰动信号进行目标测距、测深和多目标分辨的一种实现途径，为声栅栏探测技术的进一步发展提供技术支撑。