密集状态下鱼群声学散射特性研究

Underwater acoustic measurement technology is an effective method for the investigation of marine organisms and the estimation of fishery resources. Which as a basic hypothesis that the biological acoustic backscattering measurement has a linear relationship with Biomass. Although the hypothesis is effective in most applications.in experimental measurements and application research, we find biomass estimation accuracy decline obviously, because multiple acoustic scatter in concentrated school make the linear hypothesis failure. This project aims to research the acoustic backscattering characteristics of concentrated fish school, in which, acoustic measurement of concentrated school has a nonlinear relationship with Biomass estimation. We will adopt the broadband acoustic measurement system with frequencies coverage from 10kHz to 200kHz and aquaculture net cage as test platform to research fish school acoustic backscattering characteristics. Based on the analysis of multiple backscattering on the acoustic backscattering of concentrated school which look as an effective media ，the acoustic backscattering numerical simulation model is developed through researching the relationship between acoustic multiple backscattering and density of school、size of individual fish and frequency. Compared to controlled Laboratory measurements, the relationship between acoustic backscattering strength of concentrated school and fishes biomass estimation is revealed when they does not satisfy the linear Hypothesis. Moreover, the biomass estimation and calculation method of marine biological resources are proposed in the project. Therefore, this research results will pay an important role for perfecting basis theory of fishery underwater acoustic an improving its applications.

声学测量技术是海洋生物和渔业资源监测、调查和评估的有效技术手段，其基本假设是生物资源量与生物体/群的目标散射强度呈线性关系。这一假设在大多数情况下成立。然而实验和研究中发现，当鱼群密集时，由于个体之间存在多次散射作用，这种线性关系将不再成立，资源量的评估的准确性下降。本项目针对渔业声学测量中不满足线性关系的密集鱼群声散射特性展开研究。采用宽频带(10kHz~200kHz)覆盖声学测量系统和可控生物群体密度的养殖网箱为实验研究平台，将密集鱼群看做等效声学介质,分析密集生物群体多次散射特性，研究散射强度与群体密度、个体尺寸及频率之间的关系，建立密集状态下，鱼群声学散射声场的数值仿真模型，结合实验数据分析，揭示密集状态下，声学测量的线性关系无法满足时，生物资源量与声学散射量之间的对应关系，提出密集生物群体资源量的准确评估和计算方法。本研究对渔业声学资源调查、评估基础理论的完善和应用有重要意义。

声学测量技术是海洋生物和渔业资源监测、调查和评估的有效技术手段，鱼群资源量评估方法研究不仅在海洋生态系统监测、鱼类的科学捕捞中具有直接的应用价值，与传统的拖网捕捞采样法相比，声学评估方法具有快捷方便，可持续观测，且不危害生物资源等优点，如何建立鱼群回波信号量与生物量之间的关系模型对于渔业资源量声学评估至关重要。. 本项目采用宽频带覆盖声学测量系统和可控生物群体密度的养殖网箱为实验研究平台，将密集鱼群看做等效声学介质,分析鱼群散射特性，研究散射强度与群体密度、个体尺寸及频率之间的关系，建立密集状态下，鱼群宽带声学散射的数值仿真模型，结合实验数据分析，（1）在单体鱼KRM建模基础上，提出了一种适用于鱼群资源量评估研究的鱼群声散射模型，考虑了鱼群密度、个体鱼回波、声纳波束指向性、发射信号参数等因素对鱼群回波信号的影响。（2）通过分析鱼群宽带回波的统计特征，建立了一种基于宽带二阶积分能量统计的鱼群资源量评估方法，以积分能量的归一化二阶量——变异系数平方作为统计特征量，以鱼群中个体鱼回波信号包络归一化幅度的分布作为模型参数，同时该方法发挥宽带回波脉冲压缩能量聚焦的优势， 大大提升了原有的窄带统计方法的鱼群资源量评估性能。（3）利用鱼群中个体鱼随机分布的特点，从统计的角度对个体鱼回波波形进行处理，建立了一种基于宽带回波相对强度统计的鱼群资源量评估方法。该方法延续了宽带二阶积分能量统计方法相对于回波积分法的优点，同时考虑了实际应用中个体鱼回波波形对评估结果的影响，增强了实用性，提高了评估性能。本项目研究为密集生物群体资源量提供了评估模型和计算方法，对渔业声学资源调查、评估基础理论的完善和应用有重要意义。