Passive sensing of head wave propagation in the ambient noise field and its implications for geoacoustic inversion

Abstract

Under certain conditions, the ambient noise field can produce and amplify head waves with unique propagation characteristics; these are detectable with a vertical line array and can be analyzed to extract geoacoustic information. Head wave phenomenon in the seabed can be observed using point sources, but these arrivals are usually very weak and difficult to detect ahead of the strong direct-path arrival. In contrast, surface-generated noise from wind and breaking waves are effectively a planar source that insonify the entire seabed at every angle and from every direction. Ambient noise head waves are conical waves that are generated when noise first reaches the seabed at the critical angle, and are amplified upon each subsequent interaction with the seabed. This interaction involves splitting the incident wave into water-borne and seabed-borne components, each separated in time by a fixed lag. A vertical line array can observe this phenomenon by cross-correlating beams steered upward and downward at the c...