Measurements of the direction of arrival, time dispersion and frequency dispersion of HF signals received over a path along the mid-latitude trough

2003 ◽  
Author(s):  
D.R. Siddle
Keyword(s):  
Arrival Time ◽  
Frequency Dispersion ◽  
Direction Of Arrival ◽  
Time Dispersion

scholarly journals TSUNAMI PHASE SPEED REDUCTION DUE TO WATER COMPRESSIBILTY

2018 ◽  
pp. 9
Author(s):  
Ali Abdolali ◽  
James T. Kirby
Keyword(s):  
Arrival Time ◽  
Phase Speed ◽  
Propagation Speed ◽  
Frequency Dispersion ◽  
Wave Theory ◽  
Polar Coordinates ◽  
Ocean Bottom ◽  
Tsunami Propagation ◽  
Boussinesq Model ◽  
Tsunami Waves

Most existing tsunami propagation models consider the ocean to be an incompressible, homogenous medium. Recently, it has been shown that a number of physical features can slow the propagation speed of tsunami waves, including wave frequency dispersion, ocean bottom elasticity, water compressibility and thermal or salinity stratification. These physical effects are secondary to the leading order, shallow water or long wave behavior, but still play a quantifiable role in tsunami arrival time, especially at far distant locations. In this work, we have performed analytical and numerical investigations and have shown that consideration of those effects can actually improve the prediction of arrival time at distant stations, compared to incompressible forms of wave equations. We derive a modified Mild Slope Equation for Weakly Compressible fluid following the method proposed by Sammarco et al. (2013) and Abdolali et al. (2015) using linearized wave theory, and then describe comparable extensions to the Boussinesq model of Kirby et al. (2013). Both models account for water compressibility and compression of static water column to simulate tsunami waves. The mild slope model is formulated in plane Cartesian coordinates and is thus limited to medium propagation distances, while the Boussinesq model is formulated in spherical polar coordinates and is suitable for ocean scale simulations.

Comparison of measured and predicted time dispersion and direction of arrival for multipath in a small cell environment

2001 ◽  
Vol 49 (9) ◽  
pp. 1254-1263 ◽  
Author(s):  
C. Kloch ◽  
G. Liang ◽  
J.B. Andersen ◽  
G.F. Pedersen ◽  
H.L. Bertoni
Keyword(s):  
Direction Of Arrival ◽  
Small Cell ◽  
Time Dispersion

Ocean Swell: How Much Do We Know

2017 ◽  
Author(s):  
Alexander V. Babanin ◽  
Haoyu Jiang
Keyword(s):  
Wave Amplitude ◽  
Arrival Time ◽  
Frequency Dispersion ◽  
Nonlinear Effects ◽  
Joint Analysis ◽  
Wave Forecast ◽  
Model Predictions ◽  
Forecast Models ◽  
Maritime Operations ◽  
Definition Of

Swell waves are present in more than 80% of ocean seas, and provide significant adverse impact on maritime operations. Their prediction by wave-forecast models, however, is poor, both in terms of wave amplitude and, particularly, arrival time. The very definition of ocean swell is ambiguous: while it is usually perceived as former wind-generated waves, in fact it may reconnect with the local wind through nonlinear interactions. The paper will bring together an overview of the complex swell problem. The visible swell attenuation is driven by a number of dissipative and non-dissipative processes. The dissipative phenomena include interaction with turbulence on the water and air sides, with adverse winds or currents. Non-dissipative contributions to the gradual decline of wave amplitude come from frequency dispersion, directional spreading, refraction by currents, and lateral diffraction of wave energy. The interactions with local winds/waves can, on the contrary, cause swell growth. Swell arrival time is the least understood and the most uncertain problem. Joint analysis of buoy observations and model reanalysis shows that swell can be tens of hours early or late by comparison with model predictions. Linear and nonlinear effects which can contribute to such biases are discussed.

Estimation of Direction of Arrival of Fish Calls in a Chorus Using Stereo Hydrophones

2017 ◽  
Vol 51 (4) ◽  
pp. 68-75
Author(s):  
Masanori Ito ◽  
Ikuo Matsuo ◽  
Tomohito Imaizumi ◽  
Tomonari Akamatsu
Keyword(s):  
Arrival Time ◽  
Direction Of Arrival ◽  
Recording System ◽  
Fish Ecology ◽  
Multiple Sources ◽  
White Croaker ◽  
Or Groups ◽  
Pennahia Argentata ◽  
And Behavior ◽  
Insight Into

AbstractSome fish species produce sounds consisting of periodic pulses that are associated with distinct behaviors (e.g., courtship). Thus, the ability to estimate the direction of arrival from recorded sounds could provide insight into fish ecology and behavior. A stereo recording system was used to monitor underwater fish call sounds. The recorded signals were subjected to automatic processing to detect sounds that had the characteristics of fish calls. The direction of arrival for each detected sound was then estimated using the arrival time difference between the two hydrophones. Simulations confirmed that the recording system could accurately estimate the direction of arrival of fish call sounds. Furthermore, a blind source separation method was used to separate detected sounds originating from multiple individuals or groups of fish. Using this method, the direction of arrival for calls from multiple sources was estimated. The method described in this paper was successfully applied to monitor and isolate sounds from white croaker (Pennahia argentata) in the ocean.

Wave Dispersion Effect in the Indian Ocean Tsunami

2006 ◽  
Vol 1 (1) ◽  
pp. 142-147 ◽  
Author(s):  
Yoshinori Shigihara ◽  
◽  
Koji Fujima
Keyword(s):  
Indian Ocean ◽  
Arrival Time ◽  
Frequency Dispersion ◽  
Wave Dispersion ◽  
Tsunami Source ◽  
Indian Ocean Tsunami ◽  
Dispersion Effect ◽  
The Indian Ocean ◽  
Process Dispersion ◽  
Runup Height

We conducted a numerical simulation that takes into account the effect of wave frequency dispersion in the Indian Ocean Tsunami that occurred on December 26, 2004. A leapfrog-implicit numerical scheme based on Shigihara et al. [6] is applicable to practical simulation. Dispersion effect is negligible for the runup to the northwest coast of Sumatra Island. At the west side of tsunami source, if the aim of simulation is the reproduction of detailed propagation process, dispersion should be considered in Sri Lanka. If maximum runup height and tsunami arrival time are required, however, dispersion may be negligible.

Influence of Filter Frequency Dispersion on Soliton Arrival Time Jitter

1996 ◽  
Vol 2 (2) ◽  
pp. 134-142
Author(s):  
Thierry Georges ◽  
Benoı̂t Charbonnier ◽  
François Favre
Keyword(s):  
Arrival Time ◽  
Frequency Dispersion ◽  
Time Jitter ◽  
Filter Frequency

scholarly journals Detection and blind channel estimation for UAV-aided wireless sensor networks in smart cities under mobile jamming attack

2021 ◽  
Author(s):  
Donatella Darsena ◽  
Giacinto Gelli ◽  
Ivan Iudice ◽  
Francesco Verde
Keyword(s):  
Wireless Sensor Networks ◽  
Sensor Networks ◽  
Smart Cities ◽  
Multipath Propagation ◽  
Frequency Dispersion ◽  
Wireless Sensor ◽  
Modulation Format ◽  
Jamming Attack ◽  
Time Dispersion ◽  
Detector Output

Unmanned aerial vehicles (UAVs) can be integrated into wireless sensor networks (WSNs) for smart city applications in several ways. Among them, a UAV can be employed as a relay in a “store-carry and forward” fashion by uploading data from ground sensors and metering devices and, then, downloading it to a central unit. However, both the uploading and downloading phases can be prone to potential threats and attacks. As a legacy from traditional wireless networks, the jamming attack is still one of the major and serious threats to UAV-aided communications, especially when also the jammer is mobile, e.g., it is mounted on a UAV or inside a terrestrial vehicle. In this paper, we investigate anti-jamming communications for UAV-aided WSNs operating over doubly-selective channels in the downloading phase. In such a scenario, the signals transmitted by the UAV and the malicious mobile jammer undergo both time dispersion due to multipath propagation effects and frequency dispersion caused by their mobility. To suppress high-power jamming signals, we propose a blind physical-layer technique that jointly detects the UAV and jammer symbols through serial disturbance cancellation based on symbol-level post-sorting of the detector output. Amplitudes, phases, time delays, and Doppler shifts – required to implement the proposed detection strategy – are blindly estimated from data through the use of algorithms that exploit the almost-cyclostationarity properties of the received signal and the detailed structure of multicarrier modulation format. Simulation results corroborate the anti-jamming capabilities of the proposed method, for different mobility scenarios of the jammer.

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