Low‐frequency backscatter from near‐surface bubble plumes

1993 ◽  
Vol 94 (3) ◽  
pp. 1784-1784
Author(s):  
Jeffrey A. Schindall ◽  
Ronald A. Roy ◽  
Lawrence A. Crum ◽  
William M. Carey
Keyword(s):  
Low Frequency ◽  
Near Surface ◽  
Bubble Plumes ◽  
Surface Bubble

Effects of Wind-Induced Near-Surface Bubble Plumes on the Performance of Underwater Wireless Acoustic Sensor Networks

2016 ◽  
Vol 16 (11) ◽  
pp. 4092-4099 ◽  
Author(s):  
Amit Kumar Mandal ◽  
Sudip Misra ◽  
Tamoghna Ojha ◽  
Mihir Kumar Dash ◽  
Mohammad S. Obaidat
Keyword(s):  
Sensor Networks ◽  
Acoustic Sensor ◽  
Near Surface ◽  
Bubble Plumes ◽  
Acoustic Sensor Networks ◽  
Surface Bubble

FDTD modeling of low‐frequency sea surface reverberation in the presence of a near‐surface bubble layer

2000 ◽  
Vol 107 (5) ◽  
pp. 2922-2922
Author(s):  
Richard S. Keiffer ◽  
Robert A. Zingarelli ◽  
Jorge C. Novarini
Keyword(s):  
Low Frequency ◽  
Sea Surface ◽  
Near Surface ◽  
Bubble Layer ◽  
Surface Bubble

scholarly journals Large Temperature Fluctuations due to Cold-Air Pool Displacement along the Lee Slope of a Desert Mountain

2017 ◽  
Vol 56 (4) ◽  
pp. 1083-1098 ◽  
Author(s):  
Matthew E. Jeglum ◽  
Sebastian W. Hoch ◽  
Derek D. Jensen ◽  
Reneta Dimitrova ◽  
Zachariah Silver
Keyword(s):  
Low Frequency ◽  
Temperature Fluctuations ◽  
Atmospheric Modeling ◽  
Large Temperature ◽  
Complex Flow ◽  
Near Surface ◽  
Cold Air ◽  
Flow Interactions ◽  
Initial Drop ◽  
Program Temperature

AbstractLarge temperature fluctuations (LTFs), defined as a drop of the near-surface temperature of at least 3°C in less than 30 min followed by a recovery of at least half of the initial drop, were frequently observed during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program. Temperature time series at over 100 surface stations were examined in an automated fashion to identify and characterize LTFs. LTFs occur almost exclusively at night and at locations elevated 50–100 m above the basin floors, such as the east slope of the isolated Granite Mountain (GM). Temperature drops associated with LTFs were as large as 13°C and were typically greatest at heights of 4–10 m AGL. Observations and numerical simulations suggest that LTFs are the result of complex flow interactions of stably stratified flow with a mountain barrier and a leeside cold-air pool (CAP). An orographic wake forms over GM when stably stratified southwesterly nocturnal flow impinges on GM and is blocked at low levels. Warm crest-level air descends in the lee of the barrier, and the generation of baroclinic vorticity leads to periodic development of a vertically oriented vortex. Changes in the strength or location of the wake and vortex cause a displacement of the horizontal temperature gradient along the slope associated with the CAP edge, resulting in LTFs. This mechanism explains the low frequency of LTFs on the west slope of GM as well as the preference for LTFs to occur at higher elevations later at night, as the CAP depth increases.

Dispersion relations, rays and ray splitting in magnetohelioseismology

2005 ◽  
Vol 364 (1839) ◽  
pp. 333-349 ◽  
Author(s):  
P.S Cally
Keyword(s):  
Strong Field ◽  
Mode Conversion ◽  
Low Frequency ◽  
Active Regions ◽  
Dispersion Relations ◽  
Near Surface ◽  
Wave Splitting ◽  
Proper Account ◽  
Acoustic Dispersion ◽  
Field Inclination

Local helioseismology seeks to probe the near surface regions of the Sun, and in particular of active regions. These are distinguished by their strong magnetic fields, yet current local techniques do not take proper account of this. Here, we first derive appropriate gravito-magneto-acoustic dispersion relations, and then use these to examine how acoustic rays entering regions of strong field split into fast and slow components, and the subsequent fates of each. Specifically, two types of transmission point, where wave energy can transfer from the fast to slow branch (or vice versa) are identified; one close to the equipartition level where the sound and Alfvén speeds coincide, and one higher up near the acoustic cutoff turning point. This second type only exists for rays of low frequency or low l though. In accord with recent studies of fast-to-slow mode conversion from the perspective of p-modes, magnetic field inclination is found to have significant consequences for wave splitting.

scholarly journals Air-temperature control on diurnal variations in microseismicity at Laohugou Glacier No. 12, Qilian Mountains

2019 ◽  
Vol 60 (79) ◽  
pp. 125-136 ◽  
Author(s):  
Tao Zhang ◽  
Yuqiao Chen ◽  
Min Ding ◽  
Zhongyan Shen ◽  
Yuande Yang ◽  
...  
Keyword(s):  
Short Duration ◽  
Crack Opening ◽  
Low Frequency ◽  
Local Stress ◽  
Stress Concentrations ◽  
Night Time ◽  
Strong Negative Correlation ◽  
Near Surface ◽  
Temperature Change Rate ◽  
Trigger Algorithm

ABSTRACTWe conducted a 9-d seismic experiment in October 2015 at Laohugou Glacier No. 12. We identified microseismic signals using the short-term/long-term average trigger algorithm at four stations and classified them as long and short-duration events based on waveform, frequency, duration and magnitude characteristics. Both categories show systematical diurnal trends. The long-duration events are low-frequency tremor-like events that mainly occurred during the daytime with only several events per day. These events lasted tens of seconds to tens of minutes and are likely related to resonance of daytime meltwater. The dominant short-duration events mostly occurred during the night time with a peak occurrence frequency of ~360 h−1. Their short-duration (<0.2 s), high frequency (20–100 Hz) and dominance of Rayleigh waves are typical of events for near-surface crack opening. A strong negative correlation between the hourly event number and temperature change rate suggests that the occurrence of night-time events is controlled by the rate of night-time cooling. We estimated the near-surface tensile stress due to thermal contraction at night to be tens of kilopascals, which is enough to induce opening of surface cracks with pre-existing local stress concentrations, although we cannot exclude the effect of refreezing of meltwater produced during the day.

Temporal coherence of acoustic signals propagating through the near surface bubble layer

2002 ◽  
Vol 112 (5) ◽  
pp. 2424-2424
Author(s):  
R. Lee Culver ◽  
David Bradley ◽  
Jon Reeves
Keyword(s):  
Acoustic Signals ◽  
Temporal Coherence ◽  
Near Surface ◽  
Bubble Layer ◽  
Surface Bubble

Distribution of zooplankton inferred from hydroacoustic backscatter data in coastal waters off Ningaloo Reef, Western Australia

2002 ◽  
Vol 53 (6) ◽  
pp. 1005 ◽  
Author(s):  
Steven G. Wilson ◽  
Timothy Pauly ◽  
Mark G. Meekan
Keyword(s):  
Western Australia ◽  
Coastal Waters ◽  
Near Surface ◽  
Rhincodon Typus ◽  
Ningaloo Reef ◽  
The North ◽  
Whale Sharks ◽  
Bubble Layer ◽  
Surface Bubble

Hydroacoustic surveys were used to examine zooplankton distributions in coastal waters off Ningaloo Reef, Western Australia. Surveys were timed to coincide with the seasonal aggregation of whale sharks, Rhincodon typus, and other large zooplanktivores in these waters. The surveys examined scattering features of lagoon/shelf fronts, a series of cross-shelf transects and waters surrounding whale sharks swimming at the surface. These suggested that lagoon waters flow intrusively into shelf waters at reef passages in a layered exchange. Cross-shelf transects identified three vertical scattering layers: a surface bubble layer; a near-surface minimum layer; and a bottom maximum layer. Regions of intense mixing of lagoon and shelf waters were detected seaward and to the north of reef passages. Integrated acoustic mean volume backscatter of the bottom maximum layer increased with depth and distance offshore. Large subsurface aggregations of unidentified fauna were detected beneath whale sharks in the same area that manta rays and surface schools of euphausiids were also observed.

Combination of Active and Passive Seismic Analyses for Embankment Characterization

2015 ◽  
Vol 771 ◽  
pp. 179-182 ◽  
Author(s):  
Yekti Widyaningrum ◽  
Sungkono ◽  
Alwi Husein ◽  
Bagus Jaya Santosa ◽  
Ayi S. Bahri
Keyword(s):  
Rayleigh Wave ◽  
High Frequency ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Standard Penetration Test ◽  
Near Surface ◽  
Combining Data ◽  
Passive Seismic ◽  
Estimate Dispersion ◽  
Rayleigh Wave Dispersion

Rayleigh wave dispersion is intensively used to determine near surface of shear wave velocity (Vs). The method has been known as non-invasive techniques which is costly effective and efficient to characterize subsurface. Acquisition of the Rayleigh wave can be approached in two ways, i.e. passive and active. Passive seismic is accurate to estimate dispersion curve in low frequency, although it is not accurate for high frequency. While active seismic is vice versa of passive seismic. The high frequency of Rayleigh wave dispersion reflects to near surface and vice versa. Therefore, we used the combination of both passive and active seismic method to overcome the limitations of each method. The Vs which is resulted by inversion of the combining data gives accurate model if compared to log and standard penetration test (N-SPT) data. Further, the approach has been used to characterize LUSI (Lumpur Sidoarjo) embankments. The result shows that embankment material (0-12 m) has higher Vs than that lower embankment material.

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