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

为了发展海洋声层析成像技术，对远距离传播声进行估计是非常重要的。开发了两个精确的计算机模拟程序，以获得声音在洋流中的传播特性。采用Douglas算子格式研究了广角抛物方程（PE）的求解方法，该方法具有很高的精度。精确的PE计算方法表明，该方法适用于深海和浅水声传播的计算。用PE法求解ASA基准问题的结果与其他方法吻合较好。本文还提出了一种时域有限差分法（FDTD），用于计算海底有损浅水中传播声。FDTD方法考虑了有耗海床的衰减，解决了PE II研讨会讨论的测试问题。它计算了连续波投射时声压的等高线图。并计算了传输损耗随距离的变化规律。其计算结果与海底和水中的耦合模态计算结果吻合较好。时域有限差分法还能够显示同一模型中传播的脉冲波形。结果表明，入射脉冲从凸型海床顶部返回。并给出了直接波与反射波之间的干涉波。这些结果表明了时域有限差分法的有效性。

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.