A modified complex starting field for shipping traffic noise modeling

Abstract

In current ambient noise modeling efforts, commercial shipping is considered a major contributor to overall noise levels and is modeled accordingly. The propagation of shipping noise from the many sources to the receiver is effected by use of any of a number of high‐fidelity acoustic models. Almost all of these models require an initial condition in the form of a vertical pressure field that is stepped out numerically in range. This starting field usually takes one of several forms: a simple or modified Gaussian distribution around a source depth, a normal mode starter, a simple image (acoustic dipole) starter, or a Pade‐approximated parabolic equation starting field. The implications of a near surface source are discussed, as well as effects of low‐ versus high‐angle propagation models and the effects of complex reflection from the necessarily turbulent surface. Additionally, the use of the Gaussian distribution as a sufficient starting approximate is analyzed for long‐range, deep‐water results. [Work supported by ONR and NRL.]