沿海声层析数据同化研究

Coastal Acoustic Tomography (CAT) can obtain large-scale, long-term synchronous observations of the ocean’s interior, using only a few instruments, and thus has considerable advantages over other methods, and potentially wide applications. The project team has introduced the technique of CAT to China, and utilized it there for the first time. The aim of this project is to assimilate the CAT observational data into the Finite-Volume Community Ocean Model (FVCOM), which is a numerical model based on unstructured grids, and is applicable to coastal regions. The research primarily consists of : (1) constructing a sound transmission model, based on the spatial relationship of sound transmission lines within a triangular grid coordinate system; then (2) determining the precise projector in the unstructured triangular grid from the reciprocal travel time difference to velocity status vector, thus achieving the conversion from acoustic observational data to current field data; and (3) utilizing an ensemble Kalman filter technique to assimilate the observed travel time difference data from CAT into the FVCOM model. We will use observational data from some typical coastal regions of China to verify our results. By comparing the model results with observations obtained using common techniques, and then analyzing the model errors, we will modify the assimilation model and verify its reliability. The final aim of this project is to establish a CAT assimilation model suitable for the coastal current fields in China, which will provide the necessary technological support for coastal dynamical environment forecasts in China, facilitating marine science research.

沿海声层析观测能够用较少的仪器进行海域内部大范围的长期同步观测，具有潜在的优势和应用前景。项目组通过前期努力，已基本把沿海声层析技术引进到了我国，实现了沿海声层析技术在我国的初步应用。本项目主要目标是要把沿海声层析观测数据同化到适合近海的非结构网格海洋数值模式（FVCOM）中去。主要研究内容有：根据声线和三角网格的空间关系，建立三角网格坐标下的声传播模式，进而建立双向传播时间差与模式流速状态向量在非结构三角网格中精确的投影算子，实现声学观测数据到流场的转换；在此基础上利用集合卡尔曼滤波方法将沿海声层析观测得到的声传播时间差数据同化到FVCOM中。利用我国沿海典型海区的海上验证实验资料，通过与常规观测仪器观测结果的比较，分析误差，改进同化模式，确立同化模式的可信性。本项目的最终目标是建立和完善适合我国沿海的声层析同化模式，为我国沿海海洋动力环境的预测预报和海洋科学研究提供必要的技术支撑。

沿海声层析观测能够用较少的仪器进行海域内部大范围的长期同步观测，是获取近岸海湾、河口等的流场的绝佳观测手段。但是已有的声层析流场反演均是基于逆问题求解或者正交网格的模式同化，无法满足近岸复杂岸线的应用需求。因此需要开发出一套适用于近岸复杂岸线的声层析数据同化方案。通过本项目的研究，建立了声线和三角网格的空间关系，从而确立双向传播时间差与模式流速状态向量在非结构三角网格中精确的投影算子，实现了声学观测数据到流场的转换；在此基础上利用集合卡尔曼滤波方法，成功地将沿海声层析观测得到的声传播时间差数据同化到了三维水动力海洋数值模式（FVCOM）中。项目组进一步将该同化方法应用到三门湾、胶州湾、大连湾等海域，得到了岛屿周边精细的三维流场结构。流速验证结果也显示，数据同化得到的流场具有最高的反演精度。从而证明了该同化方案的可信性以及在中国近岸的适用性。项目组还利用同化得到的流场数据阐明了非线性潮、潮流涡、内潮等的时空变化及生成机制。项目组在GRL、JGR、ECSS等海洋学主流SCI杂志上共发表学术论文29篇，出版专著1本。.总体而言，本项目成功实现了三角网格声层析数据同化，并在我国近岸得到了初步应用。这标志着我国对沿海声层析的研究又迈上一个新的台阶，距离实用阶段仅一步之遥。项目的研究成果预计可在我国沿海的海洋动力环境监测和预报乃至国防安全建设等方面发挥重要作用。