THE INFLUENCE OF THE REFERENCE WAVENUMBER IN COMPUTATIONAL OCEAN ACOUSTICS

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.