Levin's collocation method for predicting sound fields in the presence of sound speed gradients

Sound propagation in a stratified medium has been studied for decades. The Ray tracing method, which is one of the most popular methods, calculates the ray path and propagating angle of a sound ray. However, the ray method is not accurate under many circumstances compared with the wave-based numerical schemes. The Fast field program (FFP), an efficient method for numerical evaluation of the Fourier integral, is accurate but requires significant computational resources for high frequency sound fields because of the highly oscillatory functions found in the integrand. In this paper, a Levin’s collocation method is introduced and used in the evaluation of the sound fields above a locally reacting ground with the presence of the sound speed gradient. The method is far more efficient than most other available numerical techniques such as the FFP and Parabolic Equation method.