Airguns: Theory and operation of the marine seismic source
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A detailed knowledge of the radiation field of seismic sources is essential to effective source design and source wavefield deconvolution. To understand the principles of airgun theory and operation it is necessary to follow the motion of the air bubble that is produced and released underwater by the airgun. An airgun is a mechanical device that releases a high pressure bubble of air underwater, the expansion of the air bubble generates seismic waves the water that are the source waves of the seismic waves used in reflection seismology. This monograph is about the motion of the bubble of air in the water that creates the seismic pressure wave called the airgun signature. The relevant physical principles for a single bubble are discussed first, then the dynamic behavior of the bubble is derived from the basic equations of fluid mechanics for the ocean and thermodynamics for the air. The surface ghost reflection part of the signature is derived and its behavior explained. Once the dynamics of a single bubble is understood, the behavior of an array of airgun bubbles is easy to understand, the reasons for an array are explained and detailed. The discussion then moves on to practical performance specifications in the field. The different types of airguns are discussed and their mechanical operation explained, this leads to the airgun system, a pneumatic-electrical computer controlled system on board the seismic vessel under the control of the GPS navigation system.