Airgun arrays for marine seismic surveys - Physics and directional characteristics

Abstract

Airgun arrays are by far the most commonly used offshore seismic survey sound sources and, despite ongoing attempts to develop alternatives, are likely to remain so well into the future. Although designed to produce their highest sound levels in the vertically downward direction, these arrays also emit considerable acoustic energy in other directions, thus making them a potential hazard for marine animals. Each airgun array produces a complicated sound field, determined by the array layout (positions and sizes of its airguns), in which both the waveform and spectrum of the signal vary strongly with direction. This paper examines the relationship between the array layout and the directional characteristics of the sound field it produces with a view to providing guidance on how changes in array layout can be used to reduce the environmental impact of an array while retaining its utility as a seismic survey source.