scholarly journals Fieldable Impulsive Source and Timer (FIST)

2018 ◽  
Author(s):  
Cheng Ho ◽  
Janette Rose Frigo ◽  
William Brian Haynes
Keyword(s):  
Impulsive Source

scholarly journals Impulsive source of the 2017, Mw =7.3, Ezgeleh, Iran, earthquake

2019 ◽  
Author(s):  
Baptiste Gombert ◽  
Zacharie Duputel ◽  
Elham Shabani ◽  
Luis Rivera ◽  
Romain Jolivet ◽  
...  
Keyword(s):  
Impulsive Source

scholarly journals Elastic properties of floating sea ice from air-coupled flexural waves

2021 ◽  
Author(s):  
Rowan Romeyn ◽  
Alfred Hanssen ◽  
Bent Ole Ruud ◽  
Tor Arne Johansen
Keyword(s):  
Sea Ice ◽  
Elastic Properties ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Flexural Wave ◽  
Ice Thickness ◽  
Linear Filter ◽  
Flexural Stiffness ◽  
Flexural Waves ◽  
Impulsive Source

Abstract. Air-coupled flexural waves appear as wave trains of constant frequency that arrive in advance of the direct air-wave from an impulsive source travelling over a floating ice sheet. The frequency of these waves varies with the flexural stiffness of the ice sheet, which is controlled by a combination of thickness and elastic properties. We develop a theoretical framework to understand these waves, utilizing modern numerical and Fourier methods to give a simpler and more accessible description than the pioneering, yet unwieldly analytical efforts of the 1950's. Our favoured dynamical model can be understood in terms of linear filter theory and is closely related to models used to describe the flexural waves produced by moving vehicles on floating plates. We find that air-coupled flexural waves are a robust feature of floating ice-sheets excited by impulsive sources over a large range of thicknesses, and we present a simple closed-form estimator for the ice thickness. Our study is focussed on first-year sea ice of ~20–80 cm thickness in Van Mijenfjorden, Svalbard, that was investigated through active source seismic experiments over four field campaigns in 2013, 2016, 2017 and 2018. The air-coupled flexural frequencies for sea-ice in this thickness range are ~60–240 Hz. While air-coupled flexural waves for thick sea-ice have received little attention, the higher frequencies associated with thin ice on fresh water lakes and rivers are well known to the ice-skating community and have been reported in popular media. Estimation of ice physical properties, following the approach we present, may allow improved surface wave modelling and wavefield subtraction in reflection seismic studies where flexural wave noise is undesirable. On the other hand, air-coupled flexural waves may also permit non-destructive continuous monitoring of ice thickness and flexural stiffness using simple, relatively inexpensive microphones located in the vicinity of the desired measurement location, either above the ice-sheet or along the shoreline. In this case, naturally forming cracks in the ice may be an appropriate impulsive source capable of exciting flexural waves in floating ice sheets in a passive monitoring context.

scholarly journals On impulse excitation of the global poloidal modes in the magnetosphere

2006 ◽  
Vol 24 (10) ◽  
pp. 2429-2433 ◽  
Author(s):  
P. N. Mager ◽  
D. Yu. Klimushkin
Keyword(s):  
Second Harmonic ◽  
Temporal Structure ◽  
Background Field ◽  
Plasma Pressure ◽  
Radial Structure ◽  
Combined Action ◽  
Spatio Temporal ◽  
Field Lines ◽  
Hermitian Polynomials ◽  
Impulsive Source

Abstract. Through the combined action of the field line curvature and finite plasma pressure in some regions of the magnetosphere (plasmapause, ring current) there can exist global poloidal Alfvén modes standing both along field lines and across magnetic shells and propagating along azimuth. In this paper we investigate the spatio-temporal structure of such waves generated by an impulsive source. In general, the mode is the sum of radial harmonics whose structure is described by Hermitian polynomials. For the usually observed second harmonic structure along the background field, frequencies of these radial harmonics are very close to each other; therefore, the generated wave is almost a monochromatic oscillation. But mixing of the harmonics with different radial structure causes the evolution of the initially poloidal wave into the toroidal one. This casts some doubts upon the interpretation of observed high-m poloidal waves as global poloidal modes.

Classification of impulsive-source active-sonar echoes based on a model of auditory perception

2007 ◽  
Vol 122 (5) ◽  
pp. 3088
Author(s):  
Jason E. Summers ◽  
Charles F. Gaumond ◽  
Derek Brock ◽  
Ralph N. Baer
Keyword(s):  
Auditory Perception ◽  
Active Sonar ◽  
Sonar Echoes ◽  
Impulsive Source

UAV-Deployed Impulsive Source Localization with Sensor Network

2016 ◽  
Vol 101 ◽  
pp. 104-111 ◽  
Author(s):  
William Greenwood ◽  
Hao Zhou ◽  
Jerome P. Lynch ◽  
Dimitrios Zekkos
Keyword(s):  
Data Collection ◽  
Source Localization ◽  
Concrete Slab ◽  
Time Domain Analysis ◽  
Dense Array ◽  
Impulsive Load ◽  
Aerial Vehicle ◽  
Flight Parameters ◽  
Slab Foundation ◽  
Impulsive Source

The unmanned aerial vehicle (UAV) is a light weight flight system that can carry sensors and cameras for data collection. Tremendous excitement surrounds the use of UAVs because they can be deployed easily and rapidly for data collection; they also can be programmed to execute missions with high degrees of autonomy. For these reasons, UAVs hold promise in accelerating the collection of data in geophysical explorations. In this study, a UAV platform is explored for the collection of data from geophones deployed to measure the vibrations of a concrete slab foundation. The UAV is designed to drop a weight as a controlled energy source. Both the energy and location of the impulsive load are adjustable by the flight parameters of the UAV. The study adopts a time-domain analysis for source localization using the dense array of geophones

Measurement of rise times of seismic pulses in rock

Geophysics ◽  
1982 ◽  
Vol 47 (7) ◽  
pp. 1047-1058 ◽  
Author(s):  
D. P. Blair
Keyword(s):  
Measurement System ◽  
Rise Time ◽  
Broad Band ◽  
General System ◽  
Large Contribution ◽  
Measurement Systems ◽  
Numerical Assessment ◽  
The Given ◽  
Impulsive Source ◽  
System Transfer Function

Rise times for seismic pulses in rock are discussed for both nearly constant Q (NCQ) and constant Q (CQ) theories of pulse attenuation. The frequency content of the NCQ pulse is examined in detail. Frequencies close to the megahertz region are shown to have a significant contribution to the rise time of pulses a meter or so from an impulsive source. Hence, the measurement of such rise times is significantly influenced by the frequency response of the measurement system itself. In giving a numerical assessment of the system influence, I propose a model for a general system transfer function. The effect of such a system on the measurement of rise times of seismic pulses is then obtained by convolving the system impulse response with the given seismic pulse. For even the most broad‐band seismic measurement systems presently available, rise time measurements made especially within 10 m or so of an impulsive source show a large contribution dependent upon the rise time of the measurement system itself.

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