The Basic Study Of Sound Field Computation Method Of Complicated Ocean

Sound is the only wave form which can propagate long distance in complicated ocean, whose propagation is estimated by means of numerical mode. It is important issue to invert the parameters of ocean environment by the numerical code of sound field. How to establish rapid and precise numerical mode for sound field is also the key to improve the Sonar technology.The article firstly recalls the numerical modes in existence, and summarizes the characteristics of them. Two modes– normal mode (NM) theory and parabolic equation (PE) method which are the basis of our new method are given.The numerical methods for simple oceanic wave guide are robust, which compute rapidly and accurately, for instance adiabatic normal mode theory and parabolic equation method. However, for the wave guide varying rapidly in horizontal direction, there are bigger errors for these methods. The coupling NM theory is of higher accurate, but slowly. PE method compute rapidly, but precision worse and only for far-field, moreover it is difficult to solve backward scattering component. Coupling NM-PE method (CMPE) is an improved mode for complex wave guide, can increase computing step and fits 3D problem.Considering the characteristic of CMPE method, a new method of sound field calculation which is based on normal mode theory is proposed. By solving a lower dimensional matrix problem instead of difference problem, eigenfunctions and wave numbers can be calculated more quickly. Firstly, the eigenfunctions and wave numbers of different range are calculated by matrix decomposition technique. Then, using the information of normal modes, the coefficient vectors of mode are estimated by means of resolving the difference equation with respect to range. The speed of computation is step on the juice, but the precision is degraded, for example, the accumulative error of wave numbers. And, some problem like the depth of sea being changed with range can not be resolved now. The numerical method and some simple example are given in the article, and comparing the result with other method.