Spatial structure of long‐range, low‐frequency seafloor reverberation in the Canary Basin

1990 ◽  
Vol 88 (S1) ◽  
pp. S106-S106
Author(s):  
Jonathan M. Berkson ◽  
Fredrick R. Facemire ◽  
Jay A. Wallmark
Keyword(s):  
Spatial Structure ◽  
Long Range ◽  
Low Frequency

Quantifying the Predictive Skill in Long-Range Forecasting. Part II: Model Error in Coarse-Grained Markov Models with Application to Ocean-Circulation Regimes

2012 ◽  
Vol 25 (6) ◽  
pp. 1814-1826 ◽  
Author(s):  
Dimitrios Giannakis ◽  
Andrew J. Majda
Keyword(s):  
Long Range ◽  
Ocean Circulation ◽  
Climate Models ◽  
Markov Models ◽  
Low Frequency ◽  
Model Error ◽  
Ocean Model ◽  
Coarse Grained ◽  
Predictive Skill ◽  
Relaxation To Equilibrium

Abstract An information-theoretic framework is developed to assess the predictive skill and model error in imperfect climate models for long-range forecasting. Here, of key importance is a climate equilibrium consistency test for detecting false predictive skill, as well as an analogous criterion describing model error during relaxation to equilibrium. Climate equilibrium consistency enforces the requirement that long-range forecasting models should reproduce the climatology of prediction observables with high fidelity. If a model meets both climate consistency and the analogous criterion describing model error during relaxation to equilibrium, then relative entropy can be used as an unbiased superensemble measure of the model’s skill in long-range coarse-grained forecasts. As an application, the authors investigate the error in modeling regime transitions in a 1.5-layer ocean model as a Markov process and identify models that are strongly persistent but their predictive skill is false. The general techniques developed here are also useful for estimating predictive skill with model error for Markov models of low-frequency atmospheric regimes.

Low-frequency vibrational spectroscopy: a new tool for revealing crystalline magnetic structures in iron phosphate crystals

2021 ◽  
Vol 23 (39) ◽  
pp. 22241-22245
Author(s):  
Zihui Song ◽  
Xudong Liu ◽  
Anish Ochani ◽  
Suling Shen ◽  
Qiqi Li ◽  
...  
Keyword(s):  
Lithium Ion Batteries ◽  
Long Range ◽  
Vibrational Spectroscopy ◽  
Strong Dependence ◽  
Low Frequency ◽  
Lithium Ion ◽  
Iron Phosphate ◽  
Promising Material ◽  
Vibrational Dynamics ◽  
Magnetic Structures

In this report, the strong-dependence of low-frequency (terahertz) vibrational dynamics on weak and long-range forces in crystals is leveraged to determine the bulk magnetic configuration of iron phosphate – a promising material for cathodes in lithium ion batteries.

scholarly journals Low-frequency discrete breathers in long-range systems without on-site potential

2018 ◽  
Vol 97 (6) ◽  
Author(s):  
Yoshiyuki Y. Yamaguchi ◽  
Yusuke Doi
Keyword(s):  
Long Range ◽  
Low Frequency ◽  
Discrete Breathers

scholarly journals Frequency and plasma condition dependent spatial structure of low frequency global potential oscillations in the TJ-II stellarator

2019 ◽  
Vol 59 (4) ◽  
pp. 044006 ◽  
Author(s):  
T. Kobayashi ◽  
U. Losada ◽  
B. Liu ◽  
T. Estrada ◽  
B.Ph. van Milligen ◽  
...  
Keyword(s):  
Spatial Structure ◽  
Low Frequency ◽  
Plasma Condition ◽  
Potential Oscillations

Long‐range measurements of the strength and spectral character of low‐frequency surface reverberation

1993 ◽  
Vol 94 (3) ◽  
pp. 1765-1765
Author(s):  
Roger C. Gauss ◽  
Raymond J. Soukup ◽  
David M. Fromm ◽  
Joseph M. Fialkowski
Keyword(s):  
Long Range ◽  
Low Frequency ◽  
Spectral Character ◽  
Range Measurements

scholarly journals The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

2019 ◽  
Vol 11 (21) ◽  
pp. 2464 ◽  
Author(s):  
Daniel Duane ◽  
Byunggu Cho ◽  
Ankita D. Jain ◽  
Olav Rune Godø ◽  
Nicholas C. Makris
Keyword(s):  
Remote Sensing ◽  
Long Range ◽  
Cross Sections ◽  
Electromagnetic Waves ◽  
Low Frequency ◽  
Wide Area ◽  
Line Transect ◽  
Acoustic Sensing ◽  
Underwater Acoustic ◽  
Primary Means

Acoustics is the primary means of long-range and wide-area sensing in the ocean due to the severe attenuation of electromagnetic waves in seawater. While it is known that densely packed fish groups can attenuate acoustic signals during long-range propagation in an ocean waveguide, previous experimental demonstrations have been restricted to single line transect measurements of either transmission or backscatter and have not directly investigated wide-area sensing and communication issues. Here we experimentally show with wide-area sensing over 360° in the horizontal and ranges spanning many tens of kilometers that a single large fish shoal can significantly occlude acoustic sensing over entire sectors spanning more than 30° with corresponding decreases in detection ranges by roughly an order of magnitude. Such blockages can comprise significant impediments to underwater acoustic remote sensing and surveillance of underwater vehicles, marine life and geophysical phenomena as well as underwater communication. This makes it important to understand the relevant mechanisms and accurately predict attenuation from fish in long-range underwater acoustic sensing and communication. To do so, we apply an analytical theory derived from first principles for acoustic propagation and scattering through inhomogeneities in an ocean waveguide to model propagation through fish shoals. In previous experiments, either the attenuation from fish in the shoal or the scattering cross sections of fish in the shoal were measured but not both, making it impossible to directly confirm a theoretical prediction on attenuation through the shoal. Here, both measurements have been made and they experimentally confirm the waveguide theory presented. We find experimentally and theoretically that attenuation can be significant when the sensing frequency is near the resonance frequency of the shoaling fish. Negligible attenuation was observed in previous low-frequency ocean acoustic waveguide remote sensing (OAWRS) experiments because the sensing frequency was sufficiently far from the swimbladder resonance peak of the shoaling fish or the packing densities of the fish shoals were not sufficiently high. We show that common heuristic approaches that employ free space scattering assumptions for attenuation from fish groups can lead to significant errors for applications involving long-range waveguide propagation and scattering.

scholarly journals Observations of low-frequency, long-range acoustic propagation in the Philippine Sea and comparisons with mode transport theory

2020 ◽  
Vol 147 (2) ◽  
pp. 877-897
Author(s):  
Tarun K. Chandrayadula ◽  
Sivaselvi Periyasamy ◽  
John A. Colosi ◽  
Peter F. Worcester ◽  
Matthew A. Dzieciuch ◽  
...  
Keyword(s):  
Long Range ◽  
Transport Theory ◽  
Low Frequency ◽  
Acoustic Propagation ◽  
Philippine Sea

Spatial structure of low-frequency wind noise

2007 ◽  
Vol 122 (6) ◽  
pp. EL223-EL228 ◽  
Author(s):  
D. Keith Wilson ◽  
Roy J. Greenfield ◽  
Michael J. White
Keyword(s):  
Spatial Structure ◽  
Low Frequency ◽  
Wind Noise

Exploiting the characteristics of volcanic lightning for volcano monitoring

2020 ◽  
Author(s):  
Sonja Behnke ◽  
Harald Edens ◽  
Seda Senay ◽  
Diana Swanson ◽  
Alexa Van Eaton ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Long Range ◽  
Detection Efficiency ◽  
Low Frequency ◽  
Volcano Monitoring ◽  
Volcanic Plume ◽  
Very High Frequency ◽  
New Information ◽  
Lightning Discharges ◽  
Volcanic Lightning

<p>Volcanic lightning measurements are gaining momentum in the volcano monitoring community as a tool to identify when an ash producing eruption has occurred. As a volcanic plume develops from an ash-laden jet to a convective plume, the electrical discharges also evolve, ranging from small “vent discharges” (a few meters in length) and near-vent lightning (tens of meters to kilometers in length) to thunderstorm-like plume lightning (tens of kilometers in length). Currently, volcanic lightning monitoring capabilities for volcano observatories are mainly limited to using long-range lightning sensor networks, which do not detect the full gamut of volcanic lightning due to the networks’ detection efficiency and the radio frequency band that they use (very low frequency or low frequency). This biases the sensors towards detecting only the larger volcanic lightning discharges that occur at later stages in plume development, which can result in detection delays of minutes to tens of minutes from the onset of eruption. In addition to the latency, there is no way to know if the lightning picked up by long range networks is from a volcanic or meteorological source without some other additional source measurement. Both the latency and the source ambiguity could be reduced by using lightning sensors at close range that can detect the very small vent discharges associated with volcanic explosions. Vent discharges occur within the gas thrust region in a plume, starting simultaneously with the onset of an eruption and persisting continually for seconds or tens of seconds, depending on the duration of an eruption. They produce a distinctive ‘continual radio frequency’ signal, of which there is no analogous signature in meteorological lightning. Thus, the characteristics of the radio frequency signature of vent discharges could be exploited to innovate a new sensor design that is both low power and transmits information (i.e., a useful derived data product) at rates low enough to be used at remote volcanoes where volcano monitoring is often sparse. To meet this goal, a new experiment at Sakurajima Volcano in Japan is underway to learn more about the physical characteristics and signal characteristics of vent discharges. We use broadband very high frequency sensors to record time series measurements of the vent discharges and other volcanic lightning discharges that occur from explosions of the Minamidake crater of Sakurajima. These measurements reveal new information about vent discharges, such as their duration and spectral features, that can be used to help identify when explosive eruptions are occurring.</p>

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