Measurements of a 20, 440, and 3130 cubic inch air gun or array off Peregian Beach Queensland and Dongara Western Australia highlight small and large scale inhomogeneous sound propagation environments

Abstract

During the project “Behavioural Response of Australian Humpback whales to Seismic Surveys” three air gun configurations were used to quantify the response of southerly migrating humpback whales to a northerly travelling air gun. Off Peregian Beach, Queensland (26.5o S latitude) a 20 cubic inch (cui) single air gun, 440 cui and 3130 cui arrays were operated while off Dongara, Western Australia (29.5o S) the 440 cui array was operated. At a first glance, we assumed within the respective ∼200 km2 experimental areas sound propagation was reasonably uniform but this was not the case. At Peregian Beach, flat supposedly sandy areas had patchy outcrops of soft “coffee” rock which dramatically increased sound propagation loss while in the north a large arc of hard reef or shallow sand over reef again increased sound propagation loss and acted as an “amphitheatre.” Off Dongara different depths of sand or no sand over a limestone base created variable sound propagation. When comparing Dongara and Peregian Beach the shallow limestone off Dongara increased propagation loss compared to Peregian. This talk will explore some of the idiosyncrasies of air gun propagation and inhomogeneities which can be expected when planning sound exposure experiments.