Low-Frequency Acoustic Propagation Modelling for Australian Range-Independent Environments

Abstract

Large portions of the Australian continental shelf have a seabed composed of layered cemented or semi-cemented calcarenite. This work investigates the ability of a wavenumber integration sound propagation model, two normal mode sound propagation models, and a parabolic equation sound propagation model to consistently predict the acoustic field over four types of calcarenite style seabeds. The four geoacoustic models that are presented here represent seabed types that are likely to be found in the Australian marine environment. Transmission loss results for each geoacoustic model are computed using each sound propagation model, which are compared over a broad band of low frequencies in order to assess their relative performance. The performance of the wavenumber integration model, SCOOTER, and the two normal mode models over a broad band of low frequencies was found to be accurate and robust for all the tested scenarios. However, for one of the normal mode models, KRAKENC, long computational runtimes were incurred to produce accurate results. The parabolic equation model RAMSGeo produced accurate transmission loss results at some of the frequencies, but it also produced some unrealistic transmission loss predictions when thin layers were present in the seabed. The normal mode model ORCA was found to have the best balance between accuracy and efficiency because it had the shortest runtimes for most of the calculation frequencies and the shortest overall runtime.