Development of wide-angle PE calculation method for long-range sound propagation in ocean current.

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In order to develop an ocean acoustic tomography technique, it is very important to estimate the long-range propagation sound. Two precise computer simulation programs were developed for obtaining the sound propagation characteristics across ocean currents. We investigated the wide-angle Parabolic Equation (PE) method using Douglas operator scheme, which was very accurate. The accurate PE calculation method showed that it was applicable for calculation of sound propagation in deep ocean and shallow water. The result of ASA benchmark problem solved by PE method agreed well with other method. We also developed the Finite Difference Time Domain (FDTD) method for calculating the propagation sound in shallow water with lossy seabed. The FDTD method, which is taking account of attenuation of a lossy seabed, solved the test problem discussed in the PE II Workshop. It calculated a contour map of the sound pressure when the continuous wave was projected. The transmission loss pattern as a function of range is also calculated. Its results agreed well with the results of a coupled-mode calculation not only in water but also in seabed. The FDTD method is also capable of visualizing the propagated pulse waveforms in the same model. It showed that the incoming pulse has returned from the top of the convex seabed. It was also shown the interference wave between direct wave and reflected waves. These results show the validity of the FDTD method.