海底沉积物中低频（500 Hz-25 kHz）地声模型及频散特性研究

The acoustic properties of seafloor sediment at the frequency from 500 Hz~25 kHz have an large influence on the sound propagation and structure of underwater acoustic field in complex conditions of shallow sea. Because of the large size of low frequency source, it is very difficult to conduct an in-situ measurement of sediment acoustic properties at low and mid frequency on the seafloor which is fully covered by water. This difficulty leads to the lack of data at low and mid frequency. As a result, the geoacoustic model and the frequency dispersion at this frequency band are not clear. In order to solve the problems mentioned-above, this project will choose three sea benches (sandy, mudy and silty) which are very similar to the in-situ seafloor environment as study areas. At first, a precise measurement of the sound speeds and attenuation coefficients of seafloor sediment at low and mid frequency (500Hz ~ 25 kHz) will be conducted in the three study areas. Secondly, the correlation between acoustic properties at low and mid frequency and physical-mechanical parameters will be analyzed based on the data obtained in study areas and the geoacoustic models will be established. Finally, different mechanisms of dispersion and attenuation of low and mid frequency propagation at different sediments will be studies and the models of frequency dispersion from 500 Hz to 25 kHz will be built up. The study will improve greatly the research level of our country in the area of sediment acoustic properties and geoacoustic models.

海底沉积物中低频（500Hz~25kHz）声学特性对浅海复杂环境下声波传播规律和声场结构具有重要影响。中低频声源体积较大，使得直接在由海水完全覆盖的海底开展中低频声学特性测量非常困难，导致目前沉积物中低频声学特性测量数据缺乏，致使中低频地声模型和频散特性研究薄弱。本项目针对目前海底沉积物声学特性、地声模型和频散模型研究存在的问题，选择与实际海底环境相似的砂质、淤泥质和粉砂质三种不同类型的滨海海滩，分别测量500Hz~25kHz中低频声速和声衰减系数等沉积物声学特性参数，分析声速和声衰减系数与物理力学性质之间的关系，研究和建立中低频沉积物地声模型；分析不同类型沉积物中低频声速和声衰减系数与频率的关系，研究声波在不同类型沉积物中传播时的频散和衰减机理，建立沉积物中低频声速和衰减频散模型。该研究对丰富海底声学理论，促进我国海底沉积物声学特性及地声模型研究的发展具有重要科学意义。

海底是水下声场的重要边界，海底沉积物声学特性是影响声波在海洋中传播规律的重要因素之一，海洋水下声场的准确预报、海底声波探测资料的精确解译等均需要准确获悉海底沉积物的声学特性。目前，我国海底沉积物声学特性和地声模型研究主要集中在高频段，缺少中低频段的沉积物声学特性、频散特性和地声模型等相关研究。本研究针对我国在海底沉积物中低频声学特性和地声模型研究方面的不足，重点开展海底沉积物中低频声学特性测量、海底沉积物中低频声学特性及地声模型研究、海底沉积物声学特性频散模型研究等三个方面的研究。. 项目完成了相关技术的研发和集成，形成了用于野外测量的中低频声源系列、弯曲元剪切波原位换能器、中低频平面换能器、宽频水听器和自容式声波采集站等仪器和海底沉积物中低频声学特性测量能力，在国内率先开展了中低频声学特性野外和实验室测量。研究了海底沉积物中低频声学特性测量数据处理方法，首次提出了基于变声速比的声速校正新方法，对在不同环境条件（不同温度和压力）下获得的声学特性数据进行了处理和校正，获取了不同类型沉积物中低频声学特性数据，研究了海底沉积物中频段声学特性与物理力学性质之间的关系，建立我国关键海域海底沉积物中低频地声模型。通过理论模型仿真研究了沉积物物性参数对声学特性与频率关系的影响及其声学特性频散机理，建立了不同类型沉积物中低频声学特性与频率关系的经验回归公式，研究了Biot模型和GS模型等频散关系模型在中低频段的适用性，建立适合中低频段的沉积物声学特性频散模型，实现了海底沉积物中低频声学特性预测。. 项目研究成果进一步拓展了现有沉积物声学特性和地声模型研究的声波频率范围，丰富了海底沉积物地声模型类型，对于深化海底沉积物声学特性理论研究具有重要的科学意义。另外，研究成果可用于海底沉积物中低频声学特性的预测，在海洋水下声场的准确预报、海底声波探测资料的精确解译等领域具有重要的应用价值和应用前景。