A bottom-diffracted surface-reflected arrival in the North Pacific observed from 15 to 3200 km

Abstract

Bottom-diffracted surface-reflected (BDSR) arrivals are a ubiquitous feature in long-range ocean acoustic propagation and are not predicted by existing forward models based on available bathymetric and bottom properties data. They were first identified in the LOAPEX Experiment in the North Pacific in 2004 where a BDSR from the side of “Seamount B” was observed from 500 to 3200 km range for an M-sequence centered at 75 Hz. In a follow-up research cruise in 2013, a BDSR was also observed from the side of “Seamount B” for ranges from 15 to 35 km and the same azimuth. Are the seafloor diffractors observed in 2004 and 2013 the same? Various measures of the diffractor location and their resolution are reviewed. Both diffractors fall within a 1km radius region. Elsewhere in the 2013 survey pairs of BDSRs were observed within a kilometer of each other. So it is possible that the two BDSR arrivals arise from two distinct and unresolvable diffractors. It is quite likely however that the two diffractor points are the same. The location of the 2004 diffractor is sufficient to explain the arrival times of the BDSR from the 2013 diffractor within the scatter of the data. [Work supported by ONR.]