基于浅海低频混响数据的海底粗糙界面参数反演

The extensive bottom roughness interface, as the necessary input parameter for reverberation, is difficult to fast acquisition and conventional bathymetric machine cannot satisfy the measurement precision. It is a big limit on capability analysis of active sonar to a large extent. Though reverberation is an exceptive interfering signal, it contains the lots of information of bottom roughness interface. So extracting such interface information from reverberation data is an effective means of remote sensing and proves a new ways to fast assessment of marine environment. The traditional reverberation model, which is based on empirical scattering theory, is severely limited when analyzing the contribution of roughness interface to reverberation field. So a new reverberation model based on the scattering which has clear physical mechanism is made to solve it. As a result, the full-wave reverberation model is based on Bass perturbation theory. The roughness interface is considered as "scattering source" in wave function, then solves it and gets sound scattering field and reverberation field. In this model, the bottom roughness interface is narrated as spectrum and characterizes backscattering strength, which provides the theory basis for extracting of bottom roughness. This research is based on the full-wave reverberation theory and the frequency dependency of backscattering due to bottom roughness interface is obtained in according with the frequency dependency of reverberation average strength and two-way propagation loss. Thereafter, the parameters of bottom roughness spectrum are extracted with clear and definite that the numerical relationship between bottom roughness spectrum and backscattering strength due to bottom roughness. Numerical simulation and experiment on sea will both give the proofs of the rationality of such method and the accuracy of the result.

海底粗糙界面是海底混响的主要散射源，很难实现大面积快速测量，而且常规海深测量仪的精度也很难达到混响计算所需的精度。浅海海底粗糙界面混响作为主动声纳的背景干扰，但同时也直接反映了海底粗糙界面的信息。基于经验散射理论的混响模型不能给出海底粗糙界面特征参数与混响声场的直接对应关系，不适合用于海底粗糙界面参数的混响反演。基于物理散射机理建立的全波动混响理论将海底粗糙界面用粗糙界面谱函数描述，给出其与混响声场的直接数值解析表达式，为海底粗糙界面的反演提供直接性的理论基础。在该模型中，海底粗糙界面各参数独立于其他环境参数，避免了参数耦合带来的反演结果的不确定性。这样，依据混响平均强度的频率特性与粗糙界面谱函数的频率特性强相关的特性，即可获取海底粗糙界面谱函数的频率特性，进一步实施分步反演粗糙界面谱函数的频率指数、相关长度和方差。

本项目面向海底厘米量级的随机起伏界面遥感技术，突破该界面难以直接快速测量的难点问题，提出了一种基于宽带混响数据的海底粗糙界面反演方法。该反演方法基于全波动混响理论模型开展。在该模型中，海底粗糙界面以统计模型的形式体现，独立于其他环境参数约束的波导衰减项，即海底混响强度可以描述为海底粗糙界面谱函数和波导衰减项的乘积。混响强度的频率特性由海底粗糙界面谱函数的频率特性和波导衰减项的频率特性共同决定。因此，基于宽带混响数据反演海底粗糙界面参数的关键在于对波导衰减项的准确估计，而对该参数的准确估计需要海底地声参数的准确先验知识。而直接表征海底地声参数的声速、密度和声吸收系数很难直接测量和反演准确，这里采用直接表征海底反射损失参数Q(f)和反射相移参数P(f)描述海底地声特性，从而准确估计波导衰减项，进而快速反演海底粗糙界面谱函数。在获取到该谱函数的频率特性之后，根据Goff-Jordan谱函数对各参数的敏感度差异，依次反演海底粗糙界面的频率指数项、方差和相关长度。该反演方法通过了海上试验验证。