The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Andrew Curtis - One of the best experts on this subject based on the ideXlab platform.
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seismic Interferometry and ambient noise tomography in the british isles
Proceedings of the Geologists' Association, 2012Co-Authors: Andrew Curtis, Heather Nicolson, Brian Baptie, Erica GalettiAbstract:Traditional methods of imaging the Earth's subsurface using seismic waves require an identifiable, impulsive source of seismic energy, for example an earthquake or explosive source. Naturally occurring, ambient seismic waves form an ever-present source of energy that is conventionally regarded as unusable since it is not impulsive. As such it is generally removed from seismic data and subsequent analysis. A new method known as seismic Interferometry can be used to extract useful information about the Earth's subsurface from the ambient noise wavefield. Consequently, seismic Interferometry is an important new tool for exploring areas which are otherwise seismically quiescent, such as the British Isles in which there are relatively few strong earthquakes. One of the possible applications of seismic Interferometry is ambient noise tomography (ANT). ANT is a way of using Interferometry to image subsurface seismic velocity variations using seismic (surface) waves extracted from the background ambient vibrations of the Earth. To date, ANT has been used successfully to image the Earth's crust and upper-mantle on regional and continental scales in many locations and has the power to resolve major geological features such as sedimentary basins and igneous and metamorphic cores. Here we provide a review of seismic Interferometry and ANT, and show that the seismic Interferometry method works well within the British Isles. We illustrate the usefulness of the method in seismically quiescent areas by presenting the first surface wave group velocity maps of the Scottish Highlands using only ambient seismic noise. These maps show low velocity anomalies in sedimentary basins such as the Moray Firth, and high velocity anomalies in igneous and metamorphic centres such as the Lewisian complex. They also suggest that the Moho shallows from south to north across Scotland which agrees with previous geophysical studies in the region.
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seismic Interferometry of scattered surface waves in attenuative media
Geophysical Journal International, 2009Co-Authors: David Halliday, Andrew CurtisAbstract:SUMMARY Seismic Interferometry can be used to estimate interreceiver surface wave signals by cross-correlation of signals recorded at each receiver that are emitted from a surrounding boundary of impulsive or uncorrelated noise sources. We study seismic Interferometry for scattered surface waves using a stationary-phase analysis and surface wave Green's functions for isotropic point scatterers embedded in laterally homogeneous media. Our analysis reveals key differences between the interferometric construction of reflected and point-scattered body or surface waves, since point scatterers radiate energy in all directions but a reflection from a finite flat reflector is specular. In the case of surface waves, we find that additional cancelling terms are introduced in the stationary-phase analysis for scattered waves related to the constraint imposed by the optical theorem for surface waves. The additional terms are of second order even for single-scattered waves, and we show that these can be highly significant in multiple-scattering cases. In attenuative media errors are introduced due to amplitude errors in these additional terms. Further, we find that as the distribution of scatterers in a medium becomes more complex the errors in correlation-type Interferometry caused by attenuation in the background medium become larger. Convolution-type Interferometry has been shown to be effective when considering electromagnetic wavefields in lossy media, and we show that this is also true for scattered surface waves in attenuating elastic media. By adapting our stationary-phase approach to this case, we reveal why convolution-type Interferometry performs well in such media: the second-order cancelling terms that appear in the correlation-type approach do not appear in convolution-type Interferometry. Finally, we find that when using both correlation- and convolution-type Interferometry with realistic source geometries (illustrative of both industrial seismics and ‘passive noise’ Interferometry), we cannot necessarily expect to produce estimates with all dominant scattering events present. This is shown to be especially important if, as proposed previously for electromagnetic applications, the convolution and correlation approaches are compared to help identify errors in the interferometric estimates.
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seismic Interferometry surface waves and source distribution
Geophysical Journal International, 2008Co-Authors: David Halliday, Andrew CurtisAbstract:SUMMARY Seismic Interferometry can be used to estimate interreceiver surface wave signals by cross-correlation of signals recorded at each receiver. The quality of the estimated surface waves is controlled by the distribution of sources exciting the cross-correlated wavefields, and it is commonly thought that only sources at or near the surface are required to generate accurate estimates. We study the role of source distribution in surface wave Interferometry for both surface and subsurface sources using surface wave Green's functions for laterally homogeneous media. We solve the interferometric integral using a Rayleigh wave orthogonality relationship combined with a stationary phase approach. Contrary to popular opinion we find that sources at depth do indeed play a role in the recovery of surface waves by Interferometry. We find that Interferometry performs well when surface sources are distributed homogeneously at the surface of the Earth. However, when this homogeneous distribution is not available amplitude errors are introduced, and when multiple modes are present strong spurious events appear and higher mode surface waves may not be correctly estimated. In order to recover higher mode surface waves we propose an additional step in the processing of surface wave data for seismic Interferometry: by separating modes and applying Interferometry to each mode individually it is possible to recover the interreceiver surface wave modes, without the artefacts introduced by limited source coverage.
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Seismic surface waves in a suburban environment: Active and passive interferometric methods
The Leading Edge, 2008Co-Authors: David Halliday, Andrew Curtis, Ed KraghAbstract:Seismic Interferometry refers to a new range of methods where inter-receiver wavefields (those that would have been recorded if one of each pair of receivers had been a source) can be estimated by cross-correlation of wavefields recorded at each of the receivers. These methods have found many applications in different fields of seismology, including creating “virtual” sources in wells under complex overburdens, computational full-wavefield modelling, and passive construction of surface wave waveforms from background noise in the Earth. Curtis et al. (2006) provide an overview of various applications of seismic Interferometry referred to herein, and more in-depth works can be found in the special supplement on Seismic Interferometry in the July-August issue of Geophysics.
David Halliday - One of the best experts on this subject based on the ideXlab platform.
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seismic Interferometry of scattered surface waves in attenuative media
Geophysical Journal International, 2009Co-Authors: David Halliday, Andrew CurtisAbstract:SUMMARY Seismic Interferometry can be used to estimate interreceiver surface wave signals by cross-correlation of signals recorded at each receiver that are emitted from a surrounding boundary of impulsive or uncorrelated noise sources. We study seismic Interferometry for scattered surface waves using a stationary-phase analysis and surface wave Green's functions for isotropic point scatterers embedded in laterally homogeneous media. Our analysis reveals key differences between the interferometric construction of reflected and point-scattered body or surface waves, since point scatterers radiate energy in all directions but a reflection from a finite flat reflector is specular. In the case of surface waves, we find that additional cancelling terms are introduced in the stationary-phase analysis for scattered waves related to the constraint imposed by the optical theorem for surface waves. The additional terms are of second order even for single-scattered waves, and we show that these can be highly significant in multiple-scattering cases. In attenuative media errors are introduced due to amplitude errors in these additional terms. Further, we find that as the distribution of scatterers in a medium becomes more complex the errors in correlation-type Interferometry caused by attenuation in the background medium become larger. Convolution-type Interferometry has been shown to be effective when considering electromagnetic wavefields in lossy media, and we show that this is also true for scattered surface waves in attenuating elastic media. By adapting our stationary-phase approach to this case, we reveal why convolution-type Interferometry performs well in such media: the second-order cancelling terms that appear in the correlation-type approach do not appear in convolution-type Interferometry. Finally, we find that when using both correlation- and convolution-type Interferometry with realistic source geometries (illustrative of both industrial seismics and ‘passive noise’ Interferometry), we cannot necessarily expect to produce estimates with all dominant scattering events present. This is shown to be especially important if, as proposed previously for electromagnetic applications, the convolution and correlation approaches are compared to help identify errors in the interferometric estimates.
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seismic Interferometry surface waves and source distribution
Geophysical Journal International, 2008Co-Authors: David Halliday, Andrew CurtisAbstract:SUMMARY Seismic Interferometry can be used to estimate interreceiver surface wave signals by cross-correlation of signals recorded at each receiver. The quality of the estimated surface waves is controlled by the distribution of sources exciting the cross-correlated wavefields, and it is commonly thought that only sources at or near the surface are required to generate accurate estimates. We study the role of source distribution in surface wave Interferometry for both surface and subsurface sources using surface wave Green's functions for laterally homogeneous media. We solve the interferometric integral using a Rayleigh wave orthogonality relationship combined with a stationary phase approach. Contrary to popular opinion we find that sources at depth do indeed play a role in the recovery of surface waves by Interferometry. We find that Interferometry performs well when surface sources are distributed homogeneously at the surface of the Earth. However, when this homogeneous distribution is not available amplitude errors are introduced, and when multiple modes are present strong spurious events appear and higher mode surface waves may not be correctly estimated. In order to recover higher mode surface waves we propose an additional step in the processing of surface wave data for seismic Interferometry: by separating modes and applying Interferometry to each mode individually it is possible to recover the interreceiver surface wave modes, without the artefacts introduced by limited source coverage.
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Seismic surface waves in a suburban environment: Active and passive interferometric methods
The Leading Edge, 2008Co-Authors: David Halliday, Andrew Curtis, Ed KraghAbstract:Seismic Interferometry refers to a new range of methods where inter-receiver wavefields (those that would have been recorded if one of each pair of receivers had been a source) can be estimated by cross-correlation of wavefields recorded at each of the receivers. These methods have found many applications in different fields of seismology, including creating “virtual” sources in wells under complex overburdens, computational full-wavefield modelling, and passive construction of surface wave waveforms from background noise in the Earth. Curtis et al. (2006) provide an overview of various applications of seismic Interferometry referred to herein, and more in-depth works can be found in the special supplement on Seismic Interferometry in the July-August issue of Geophysics.
Jason M Hogan - One of the best experts on this subject based on the ideXlab platform.
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large momentum transfer clock atom Interferometry on the 689 nm intercombination line of strontium
Physical Review Letters, 2020Co-Authors: Jan Rudolph, Thomas Wilkason, Hunter Swan, Connor M Holland, Benjamin E Garber, Samuel P Carman, Yijun Jiang, Megan Nantel, Jason M HoganAbstract:: We report the first realization of large momentum transfer (LMT) clock atom Interferometry. Using single-photon interactions on the strontium ^{1}S_{0}-^{3}P_{1} transition, we demonstrate Mach-Zehnder interferometers with state-of-the-art momentum separation of up to 141 ℏk and gradiometers of up to 81 ℏk. Moreover, we circumvent excited state decay limitations and extend the gradiometer duration to 50 times the excited state lifetime. Because of the broad velocity acceptance of the Interferometry pulses, all experiments are performed with laser-cooled atoms at a temperature of 3 μK. This work has applications in high-precision inertial sensing and paves the way for LMT-enhanced clock atom Interferometry on even narrower transitions, a key ingredient in proposals for gravitational wave detection and dark matter searches.
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large momentum transfer clock atom Interferometry on the 689 nm intercombination line of strontium
arXiv: Atomic Physics, 2019Co-Authors: Jan Rudolph, Thomas Wilkason, Hunter Swan, Connor M Holland, Benjamin E Garber, Samuel P Carman, Yijun Jiang, Megan Nantel, Jason M HoganAbstract:We report the first realization of large momentum transfer (LMT) clock atom Interferometry. Using single-photon interactions on the strontium ${}^1S_0 - {}^3P_1$ transition, we demonstrate Mach-Zehnder interferometers with state-of-the-art momentum separation of up to $141\,\hbar k$ and gradiometers of up to $81\,\hbar k$. Moreover, we circumvent excited state decay limitations and extend the gradiometer duration to 50 times the excited state lifetime. Due to the broad velocity acceptance of the Interferometry pulses, all experiments are performed with laser-cooled atoms at a temperature of $3\,\mu \text{K}$. This work has applications in high-precision inertial sensing and paves the way for LMT-enhanced clock atom Interferometry in gravitational wave detection and dark matter search proposals.
Richard M. Goldstein - One of the best experts on this subject based on the ideXlab platform.
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synthetic aperture radar Interferometry
Proceedings of the IEEE, 2000Co-Authors: P A Rosen, Scott Hensley, Ian Joughin, F K Li, S N Madsen, Ernesto Rodriguez, Richard M. GoldsteinAbstract:Synthetic aperture radar Interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristic of the surface. By exploiting the phase of the coherent radar signal, Interferometry has transformed radar remote sensing from a largely interpretive science to a quantitative tool, with applications in cartography, geodesy, land cover characterization, and natural hazards. This paper reviews the techniques of Interferometry, systems and limitations, and applications in a rapidly growing area of science and engineering.
D M Kane - One of the best experts on this subject based on the ideXlab platform.
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measuring nanoparticle size using optical surface profilers
Optics Express, 2013Co-Authors: Douglas J Little, D M KaneAbstract:Optical surface profilers are state-of-the-art instruments for measuring surface height profiles. They are not conventionally applied to nanoparticle measurements due to the presence of diffraction artifacts. Here we use a theoretical model based on wave-optics to account for diffraction-based artifacts in optical surface profilers. This then enables accurate measurement of nanoparticles size of a known geometry. The model is developed for both phase shifting Interferometry and vertical scanning Interferometry modes of operation. It is demonstrated that nanosphere radii as small as 12 nm, and nano-cylinder radii as small as 10-15 nm can be measured from a standard profile measurement using phase shifted Interferometry interpreted using the wave-optics approach.