Passive Estimation of the Ocean Seismoacoustic Environment by Extracting the Green’s Function from Ambient Noise

In the ocean, the dominant seismoacoustic noise source mechanism varies greatly across frequencies from ocean wave generated microseisms (0.05Hz-0.2Hz) to sea-surface noise (above 1kHz), including noise generated by human or biological activities. Though incoherent imaging with ocean ambient noise has been demonstrated (e.g. daylight imaging), a goal of this research is to use ambient noise, and even shipping noise, under certain conditions, to develop novel coherent imaging procedures such as tomography that typically require an active source or other noise based imaging methods in need of some coherence. Recent theoretical and experimental studies in ultrasonics, underwater acoustics and seismology have demonstrated that the time-domain Green's function (or impulse response)-TDGFbetween two points can be obtained from the cross-correlation of ambient noise recorded at these two points [Fried et al., 2008]. These results provide a means for passive imaging using only the ambient noise field without the use of active sources. A potential scenario might include long-term deployment of ocean sensing systems requiring minimum power consumption, covert operations in hostile settings, or scenarios where active sources are limited by environmental regulations (e.g., Southern California).