Analysis of Deep Seafloor Arrivals observed on NPAL04

Abstract

This report gives an overview of the analysis that was done on Deep Seafloor Arrivals since they were initially presented in Stephen et al (2009). All of the NPAL04/LOAPEX (North Pacific Acoustic Laboratory, 2004/ Long Range Ocean Acoustic Propagation Experiment) data on three ocean bottom seismometers (OBSs) at ~5,000m depth and the deepest element of the deep vertical line array (DVLA) at 4250m depth has been analyzed. A distinctive pattern of late arrivals was observed on the three OBSs for transmissions from T500 to T2300. The delays of these arrivals with respect to the parabolic equation predicted (PEP) path were the same for all ranges from 500 to 2300km, indicating that the delay was introduced near the receivers. At 500km range the same arrival was observed throughout the water column on the DVLA. We show that arrivals in this pattern converted from a PEP path to a bottom-diffracted surface reflected (BDSR) path at an off-geodesic seamount. WHOI-2012-09Page 3 of 88 Table of Contents 3 Table of Tables 4 Table of

The North Pacific Acoustic Laboratory deep-water acoustic propagation experiments in the Philippine Sea

“…The experiment was motivated in part by unexpected arrivals observed on OBSs at 5000-m depth in the Northeast Pacific from broadband signals transmitted by a ship-suspended 75-Hz source during the 2004 Long-range Ocean Acoustic Propagation Experiment (LOAPEX) Stephen et al, 2009Stephen et al, , 2012. These arrivals were named Deep SeaFloor (DSF) arrivals.…”

Deep seafloor arrivals in long range ocean acoustic propagation

“…2 were recording on their own autonomous clocks, are given in Stephen et al (Stephen et al, 2008;Stephen et al, 2012). The ranges have not changed since the 2008 technical report and are the same as in Stephen et al (2009) (Fig.…”

“…Sequences were not stacked prior to replica correlation, but SNR was further improved by incoherently stacking the magnitude of the replica-correlated traces. Further details of the processing and results at other source depths, ranges, and carrier frequencies are presented in Stephen et al (Stephen et al, 2008;Stephen et al, 2012).…”