THE INFLUENCE OF THE REFERENCE WAVENUMBER IN COMPUTATIONAL OCEAN ACOUSTICS

Abstract

A class of ocean acoustic propagation problems can be solved efficiently by the Parabolic Equation (PE) approximation method. The application of the PE method for the prediction of wave propagation introduces a new parameter, the reference wavenumber k0. This requires selection of the most appropriate k0, which is related to the reference sound speed c0. The influence on the acoustic field by the choice of c0 is rarely visible under weak range-dependent environments. Even if it is visible, the difference is small and is usually negligible since the present judicious choice of the c0 seems to provide acceptable results. When the environment is not weakly range-dependent, the choice of c0 will likely affect the computation of acoustic results. This paper examines a few different choices of c0 and analyzes how these different choices can influence the acoustic results. An application is given where the farfield wave equation represents a realistic range-dependent environment. Different choices of c0 were made for the computation of the acoustic field; as a consequence, different choices of c0 produce different acoustic results. These numerical results are not in agreement with a known reference exact solution. The differences are not too small and may be considered non-negligible. So, there is a need to make an appropriate choice of c0 in order to produce reasonable results. For the purpose of achieving satisfactory and acceptable acoustic results dealing with a PE-type equation, the requirements of the reference wavenumber will be discussed both mathematically and physically. Then, a number of computational choices of c0 will be examined, especially the k0-formula. An analysis as well as an assessment of the k0-formula will be given.