Symmetric small-aperture arrays for three-dimensional bearing estimation

2015 ◽  
Vol 138 (3) ◽  
pp. 1736-1736
Author(s):  
David C. Swanson ◽  
Richard L. Culver
Keyword(s):  
Three Dimensional ◽  
Small Aperture ◽  
Bearing Estimation ◽  
Aperture Arrays

Detection and source parameterization of small-energy fireball events in Western Alps with ground-based infrasonic arrays

2021 ◽  
Author(s):  
Giacomo Belli ◽  
Emanuele Pace ◽  
Emanuele Marchetti
Keyword(s):  
Western Alps ◽  
Apparent Velocity ◽  
Array Analysis ◽  
Small Energy ◽  
Small Aperture ◽  
Energy Estimation ◽  
Trajectory Reconstruction ◽  
Tnt Equivalent ◽  
Back Azimuth ◽  
Aperture Arrays

Summary We present infrasound signals generated by four fireball events occurred in Western Alps between 2016 and 2019 and that were recorded by small aperture arrays at source-to receiver distances < 300 km. Signals consist in a series of short-lived infrasonic arrivals that are closely spaced in time. Each arrival is identified as a cluster of detections with constant wave parameters (back-azimuth and apparent velocity), that change however from cluster to cluster. These arrivals are likely generated by multiple infrasonic sources (fragmentations or hypersonic flow) along the entry trajectory. We developed a method, based on 2D ray-tracing and on the independent optically determined time of the event, to locate the source position of the multiple arrivals from a single infrasonic array data and to reconstruct the 3D trajectory of a meteoroid in the Earth's atmosphere. The trajectories derived from infrasound array analysis are in excellent agreement with trajectories reconstructed from eyewitnesses reports for the four fireballs. Results suggest that the trajectory reconstruction is possible for meteoroid entries located up to ∼300 km from the array, with an accuracy that depends on the source-to-receiver distance and on the signal-to-noise level. We also estimate the energy of the four fireballs using three different empirical laws, based both on period and amplitude of recorded infrasonic signals, and discuss their applicability for the energy estimation of small energy fireball events ($\le 1{\rm{kt\,\,TNT\,\,equivalent}}$).

The effect of Doppler rate on small aperture bearing estimation

2016 ◽  
Vol 139 (4) ◽  
pp. 2020-2020 ◽  
Author(s):  
David C. Swanson ◽  
Robert L. Culver
Keyword(s):  
Small Aperture ◽  
Bearing Estimation

A seismic passive imaging step beyond SPAC and ReMi

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. KS63-KS72 ◽  
Author(s):  
Francesco Mulargia ◽  
Silvia Castellaro
Keyword(s):  
Passive Imaging ◽  
Small Aperture ◽  
Simple Geometry ◽  
Recording Station ◽  
Refraction Microtremor ◽  
A New Technique ◽  
Statistical Mode ◽  
The One ◽  
Aperture Arrays ◽  
The Waves

The basic property of passive imaging is that, given any two points, one of them can be taken as the source of the waves and the other as the recording station. This property can be derived from the statistical self-alignment of the rays along the vector joining the two points, and applies also to nondiffuse wavefields like seismic tremor. It provides a statistical basis for the use of the stationary phase integral, allowing passive interferometry under the mild constraint of mechanical homogeneity at a local scale. Combined with the tremor’s large spectral bandwidth, it allows one to recover the local Green’s function from spatial correlation. Furthermore, combining this property also with the azimuthal isotropy of either the wavefield or the array, and using the statistical mode as the estimator, provides a new technique to measure the local velocity dispersion in the subsoil. This technique exploits the potential of spatial autocorrelation (SPAC) and refraction microtremor (ReMi), allowing one (1) to use sparse small-aperture arrays with simple geometry, (2) to dispense with the fitting of Bessel functions, and (3) to measure, in a few minutes, the local (phase and group) wave velocity as a function of frequency of potentially all the wave-propagation modes — body and surface — and not just of the one prevailing at each frequency.

Three-dimensional reconstruction of atomic-scale composition with the position-sensitive atom probe

1992 ◽  
Vol 50 (2) ◽  
pp. 1478-1479
Author(s):  
G.D.W. Smith ◽  
A. Cerezo ◽  
C.R.M. Grovenor ◽  
T.J. Godfrey ◽  
R.P. Setna
Keyword(s):  
Mass Spectrometer ◽  
Three Dimensional ◽  
Atom Probe ◽  
Atomic Scale ◽  
Single Atom ◽  
Small Aperture ◽  
Dimensional Reconstruction ◽  
Position Sensitive ◽  
Atom Level ◽  
Scale Composition

The combination of a field ion microscope with a time-of-flight mass spectrometer provides the capability for chemical microanalysis at the single atom level. Such an instrument is termed an Atom Probe. Conventionally, the connection between the microscope and the mass spectrometer is made via a small aperture hole in the imaging screen. This defines a region on the specimen, typically about 2nm across, from which the analysis is obtained. The disadvantage of this arrangement is that other regions of the specimen cannot be examined, as ions from all but the selected area strike the image screen and therefore do not pass into the mass spectrometer. In order to overcome this problem, we have developed a version of the Atom Probe which incorporates a wide-angle position sensitive detector system. This instrument, which we have termed the POSAP, is shown schematically in figure 1. Typically, the field of view in this instrument is about 20nm across. The number of ions collected per atom layer removed from the specimen surface is therefore approximately 5,000.

Bayesian hierarchical model for variations in earthquake peak ground acceleration within small-aperture arrays

2018 ◽  
Vol 29 (3) ◽  
pp. e2497 ◽  
Author(s):  
Sahar Rahpeyma ◽  
Benedikt Halldorsson ◽  
Birgir Hrafnkelsson ◽  
Sigurjón Jónsson
Keyword(s):  
Hierarchical Model ◽  
Peak Ground Acceleration ◽  
Bayesian Hierarchical Model ◽  
Ground Acceleration ◽  
Small Aperture ◽  
Bayesian Hierarchical ◽  
Aperture Arrays

Very-small-aperture 3D infrasonic array for volcanic jet observation at Stromboli Volcano

2021 ◽  
Author(s):  
Kazuya Yamakawa ◽  
Mie Ichihara ◽  
Giorgio Lacanna ◽  
Claudia Sánchez ◽  
Maurizio Ripepe
Keyword(s):  
Elevation Angle ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Stromboli Volcano ◽  
Music Algorithm ◽  
Small Aperture ◽  
Planar Array ◽  
Back Azimuth ◽  
Frequency Functions ◽  
Volcanic Jet

Summary This study tested a very-small-aperture three-dimensional (VSA-3D) infrasonic array. A 3D array is ideal for resolving the back elevation angle (BEL), which has become important in the analysis of volcanic jet noise or geologic flows on steep mountain slopes. Although a VSA infrasonic array, with an aperture as small as a few tens of meters, has recently been shown to have a sufficient resolution of the back azimuth (BAZ) of incident signals, its BEL resolution is considered to be poor. We performed a four-element 3D array experiment with a 20-m aperture and 2-m height at the summit of Stromboli Volcano. We analyzed the direction of arrival (DOA) with the MUSIC algorithm as a function of frequency and conducted a cluster analysis for the estimated DOA–frequency functions of eruption signals. As a result, individual infrasonic signals were successfully related to eruptive vents. We also calculated the standard deviation (STD) of the DOAs in each cluster. Of the observed BAZ-STDs and BEL-STDs, 80 per cent were <2.0° and <4.6°, respectively. A comparison among the array geometries showed that the installation of a sensor above the ground, even at only 2 m, improved the BEL resolution, indicating that the VSA-3D array provides more detailed information about the wavefield than a planar array. The observed signals had higher BELs (−20° to 0°) than the vent direction (−30° to −25°) at 3–6 Hz, although signals above 20 Hz arrived from the vent direction. Our array verified that such DOA deviations were significant by the STD analysis and some tests with synthetic data. We infer that the DOA deviations do not indicate the source location and are caused by topographical diffraction.

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