A coastal acoustic tomography inverse method based on Legendre polynomials and its application in Sanmen Bay field experiment, China

Seven sets of shelf-contained type coastal acoustic tomography systems (CATs) were successfully deployed in Sammen Bay near the Taizhou city, China, during September 6 to 9, 2009 to measure tidal current structures at 3-min interval. An inverse model based on Legendre polynomials and Tikhonov regularization technology is developed to reconstruct the tidal current distributions using travel time differences obtained from the reciprocal sound transmission between the paired CAT stations. Variation of tidal current fields from food tide to ebb tide and tidal vortexes are well reconstructed. The horizontal distributions of tidal current obtained from the inverse analysis are in good agreement with that of Acoustic Doppler current Profiler (ADCP) observation and FVCOM ocean model. Comparison between CAT inversion and FVCOM model results, the spatial averaged mean square deviation (RMSD) is about 0.09 m/s for the eastward current and 0.04 m/s for the northward current, respectively. The time average RMSD between CAT inversion and ADCP measurement is 0.09 m/s for eastward current component and 0.002 m/s for northward current component, respectively. The investigation suggests that the coastal acoustic tomography inverse method based on Legendre polynomials is a promising alternative method for the ocean acoustic tomography inverse problem.