Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) - cruise report

Abstract

The Ocean Bottom Seismometer Augmentation in the North Pacific Experiment (OBSANP, June-July, 2013, R/V Melville) addresses the coherence and depth dependence of deep-water ambient noise and signals. During the 2004 NPAL Experiment in the North Pacific Ocean, in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals, we observed "deep seafloor arrivals" (DSFA) that were dominant on the seafloor Ocean Bottom Seismometer (OBS) (at about 5000m depth) but were absent or very weak on the Distributed Vertical Line Array (DVLA) (above 4250m depth). At least a subset of these arrivals correspond to bottomdiffracted surface-reflected (BDSR) paths from an out-of-plane seamount. BDSR arrivals are present throughout the water column, but at depths above the conjugate depth are obscured by ambient noise and PE predicted arrivals. On the 2004 NPAL/LOAPEX experiment BDSR paths yielded the largest amplitude seafloor arrivals for ranges from 500 to 3200km. The OBSANP experiment tests the hypothesis that BDSR paths contribute to the arrival structure on the deep seafloor even at short ranges (from near zero to 4-1/2CZ). The OBSANP cruise had three major research goals: a) identification and analysis of DSFA and BDSR arrivals occurring at short (1/2CZ) ranges in the 50 to 400Hz band, b) analysis of deep sea ambient noise in the band 0.03 to 80Hz, and c) analysis of the frequency dependence of BR and SRBR paths. On OBSANP we deployed a 32 element VLA from 12 to 1000m above the seafloor, eight short-period OBSs and four long-period OBSs and carried out a 15day transmission program using a J15-3 acoustic source. WHOI -2014 -03 OBSANP -Cruise Report

Array design considerations for exploitation of stable weakly dispersive modal pulses in the deep ocean

“…The second profile, C1, is the same as C0 with a Gaussian disturbance added in the upper ocean [23]. C1 qualitatively resembles an environment constructed from the hydrographic data in the Eastern North Pacific ocean [24].…”

Wind Sea behind a Cold Front and Deep Ocean Acoustics

“…1; Stephen et al 2014). Here we discuss a few hours of data taken on 1 July (Julian day 182) from seven systems (R. A.…”

“…Our approach is to examine in detail a single acoustic event observed during the 2013 Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) experiment in the northeastern subtropical Pacific (Stephen et al 2014). A similar approach, but with hurricane-force winds in the Atlantic, was taken by Wilson and Makris (2006).…”