Recent progress in coastal acoustic tomography in China: Experiments and data assimilation

Abstract

We will review three recent coastal acoustic tomography (CAT) experiments carried out in China: (1) A 15-day tomography experiment that was carried out for the first time in the Qiongzhou Strait to measure the major tidal current constituents, residual currents, and volume transport; (2) A high precision CAT experiment with 11 CAT systems performed in the winter of 2015 in the Dalian bay, China. The number of successful reciprocal transmission lines reached 51, which may be the highest number in ocean acoustic tomography history. The CAT results showed a very high accuracy of velocity measurements with a root-mean-square difference of 4 cm/s compared with moored ADCP measurements; (3) Rapid sampling CAT measurements were used to map the structure of nonlinear tidal (M4 and M6) currents. The results indicate that M4 is predominantly generated by the advection terms, while friction mechanisms are predominant for generating M6. Finally, we will introduce the CAT data assimilated into an unstructured triangular grid ocean model (FVCOM) using the ensemble Kalman filter scheme. The assimilated velocities agreed better with independent ADCP data than those obtained by inversion and simulation, indicating that data assimilation of the CAT data is the optimal method for reconstructing the current field.