NPAL04 OBS data analysis part 1 : kinematics of deep seafloor arrivals

Stephen, Ralph A.; Bolmer, S. Thompson; Udovydchenkov, Ilya A.; Worcester, Peter F.; Dzieciuch, Matthew A.; Uffelen, Lora J. Van; Mercer, James A.; Andrew, Rex K.; Buck, Linda J.; Colosi, John A.; Howe, Bruce M.

doi:10.1575/1912/2725

Cited by 10 publications

(15 citation statements)

References 9 publications

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“…Although some energy arrives at the OBSs at times corresponding to caustics of the PE predicted time fronts, there are large amplitude, late arrivals that occur between caustics and even after the PE predicted coda. Similar analysis was done for T500 to T2300 with similar results and is discussed in Section 4 of Stephen et al (2008). Some arrivals tentatively identified as DSZA in the 2008 and 2009 work, could actually be DSFA.…”

Section: ) Deep Shadow Zone Arrivals (Dsza)supporting

confidence: 73%

“…Section 5e) of the technical report, Stephen et al (2008), discusses these 16 arrivals in detail. It includes figures similar to Figure 1 for the T500, T1000 and T2300 transmissions (with bottom interaction in the PE models) as well as individual time-front figures of PE-model-with-bottominteraction results (T50 to T2300).…”

Section: ) Summary Of Late Arrivals For T250 To T3200 (Dvla-l20-hyd mentioning

confidence: 99%

“…Section 5 of Stephen et al (2008) ii) So far none of the NPAL investigators has observed SRBR arrivals on the DVLA or SVLA for M68.2 LOAPEX transmissions at ranges of T500 and beyond. So for the model SRBR events to agree with the data we need to increase the magnitude of SRBR relative to PE and deep shadow zone arrivals at the seafloor while simultaneously decreasing the magnitude of SRBR relative to PE predicted at SVLA and DVLA depths (particularly above 3000m).…”

Section: ) Bottom-reflected Surface-reflected Paths Along the Sourcementioning

confidence: 99%

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Analysis of Deep Seafloor Arrivals Observed on NPAL04

Stephen¹,

Bolmer²,

Udovydchenkov³

et al. 2012

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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

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Section: ) Deep Shadow Zone Arrivals (Dsza)supporting

confidence: 73%

Section: ) Summary Of Late Arrivals For T250 To T3200 (Dvla-l20-hyd mentioning

confidence: 99%

Section: ) Bottom-reflected Surface-reflected Paths Along the Sourcementioning

confidence: 99%

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Analysis of Deep Seafloor Arrivals Observed on NPAL04

Stephen¹,

Bolmer²,

Udovydchenkov³

et al. 2012

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“…(Stephen et al, 2009;Stephen et al, 2008). These arrivals are the largest magnitude event observed on OBS geophones in deep water (deeper than about 5000m), they are either not observed or are very weak on the deepest hydrophone in the DVLA (about 750m above the seafloor), and some deep seafloor arrivals occur seconds after the finale arrival.…”

Section: Bottom Interaction In Ocean Acoustic Propagationmentioning

confidence: 88%

Bottom Interaction in Ocean Acoustic Propagation

Stephen

2011

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LONG-TERM GOALSThis project addresses "the effects of environmental variability induced by ocean internal waves, internal tides and mesoscale processes, and by bathymetric features including seamounts and ridges, on the stability, statistics, spatial distribution and predictability of broadband acoustic signals..." (quote from the Ocean Acoustics web page). The long-term objective here is to understand the dominant physical mechanisms responsible for propagation and scattering in the deep ocean where the sound channel is not bottom limited. Understanding long range acoustic propagation in the ocean is essential for a broad range of Navy applications such as i) the acoustic detection of ships and submarines at long ranges, ii) avoiding detection of ships and submarines, iii) long range command and communications to submerged assets, and iv) improved understanding of the environment through which the Navy operates.Bottom interaction plays a significant role in the physics of both short and long-range ocean acoustic propagation and impacts physical models of both signals and ambient noise. As discovered on NPAL04 for controlled sources at long range (500-3200km) in deep water and frequencies around 75Hz, the sound field at the bottom is much more complex than the sound field in the ocean. The deep seafloor arrival pattern is not entirely random, but has some components that are regular, coherent and repeatable. OBJECTIVESThis project focuses on five tasks: 1) Participation on the PhilSea10 Mobile Operations (MOPS) cruise in July 2010 (three weeks, Kaohsiung-Kaohsiung). 2) Study the physical mechanisms controlling the strength of BR and SRBR paths as a function of frequency in the band 50-400Hz and ranges out to 300km or more. 3) Study the ambient noise as a function of depth and time on the NPAL04 and PhilSea10 DVLAs in the band 2-100Hz. 4) Analyze the controlled source DVLA data acquired on PhilSea09 and PhilSea10 to look for and explain "deep seafloor arrivals". 5) Further analysis of the mysterious "deep seafloor arrivals" on the NPAL04 OBSs. For convenience, we have split these five tasks into two parts, A and B. Part A is the ongoing analysis of the new "deep seafloor arrivals" observed on NPAL04 (Task 5). The first year of Part B includes the cruise participation and analysis of existing DVLA data (Tasks 1 and 3). The second year of Part B focuses on Tasks 2, 3 and 4 using all three DVLA data sets (NPAL04, PhilSea09 and PhilSea10).

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“…Unlike Figure 5-1 (at 250Hz), the SRBR time fronts here (at 75Hz) only appear clearly towards the bottom of the DVLA, possibly because the background noise is weaker. [Ilya_T500_LOAPEX_Data_75_dB_scale.pdf]" The figures are discussed in Sections 5a) and 5c) of Stephen et al (2008). …”

Section: )mentioning

confidence: 99%