Investigation for Improvements in the Reconstruction of Tidal Currents by Coastal Acoustic Tomography with Data Assimilation

One of the factors affecting the performance of the numerical ocean model for coastal tidal currents is the open boundary conditions that drive the model interior. This study investigated the use of reciprocal acoustic transmission and resulting path-averaged currents to adjust the open boundary conditions. The boundary conditions were generated by utilizing state estimation results of sequential data assimilation with an ensemble Kalman filter scheme. Two modified open boundary conditions were evaluated: modifying the harmonic constants and directly using the time series of the EnKF results for the normal velocity. Both the two models with the new open boundary condition improved the agreement with the observed path-averaged currents. The model with the time series of the EnKF results partly reconstructed spike-like variation found in the observed path-averaged currents. Yet, high-frequency variation in the observed path-averaged currents cannot be reproduced in detail. Further consideration will be needed to improve the model so that it can reproduce the observed path-averaged currents including their high-frequency variation.