Bottom-diffracted surface-reflected arrivals in the Philippine Sea

Abstract

Bottom-diffracted surface-reflected (BDSR) arrivals were first identified in the 2004 Long-range Ocean Acoustic Propagation Experiment (LOAPEX) in the North Pacific (Stephen et al., 2013, JASA, 134, 3307–3317). For sources at long ranges in deep water, they can be observed throughout the water column, but at depths above the conjugate depth they are obscured by ambient noise and energy propagating in the ocean sound channel (PE predicted arrivals). In deep water (deeper than the conjugate depth), ambient noise and PE predicted arrivals are sufficiently quiet that BDSR paths, scattered from small seamounts, can be the largest amplitude arrivals observed. In the Ocean Bottom Seismometer Augmentation in the Philippine Sea (OBSAPS) Experiment in April–May 2011, we observed BDSR arrivals on ocean bottom seismometers at relatively short ranges (less than 50 km). The experiment was designed to further define the characteristics of the BDSRs and to understand the conditions under which BDSRs are excited and propagate. BDSR arrivals are distinct, with little indication of coda or reverberation, and the scattering point appears to be discrete. The BDSR mechanism provides a means for acoustic signals and noise from distant sources to appear with significant strength on the deep seafloor. [Work supported by ONR.]