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Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces
Published on: July 26, 2016
Passive imaging in nondiffuse acoustic wavefields.
Francesco Mulargia1, Silvia Castellaro
1Dipartimento di Fisica, Settore di Geofisica, Università di Bologna, Italy.
Physical Review Letters
|June 4, 2008
Summary
Diffuse acoustic wavefields allow any two points to act as source and receiver. This property extends to seismic noise, enabling clearer passive imaging in anisotropic fields.
Area of Science:
- Geophysics
- Acoustics
- Wavefield analysis
Background:
- Diffuse acoustic wavefields exhibit a source-receiver symmetry between any two points.
- This symmetry arises from array azimuthal selectivity and Huygens principle in isotropic wavefields.
- Understanding wavefield properties is crucial for passive imaging techniques.
Purpose of the Study:
- To investigate the applicability of source-receiver symmetry in non-diffuse wavefields.
- To determine constraints for passive imaging in anisotropic wavefields.
- To validate theoretical predictions with seismic noise experiments.
Main Methods:
- Theoretical analysis of acoustic wavefield properties in isotropic and anisotropic media.
- Application of array azimuthal selectivity and Huygens principle.
- Experimental validation using seismic noise data in Venice, Italy.
Main Results:
- The source-receiver symmetry property holds approximately in anisotropic, azimuthally uniform wavefields without time reversal.
- This implies less stringent conditions for passive imaging compared to diffuse fields.
- Seismic noise fields, though generally non-diffuse, are compatible with finite aperture anisotropic uniform wavefields.
Conclusions:
- Passive imaging using seismic noise is feasible under less restrictive conditions than previously thought.
- Anisotropic uniform wavefields offer a practical model for seismic noise analysis.
- Experimental results confirm the theoretical framework for passive seismic imaging.
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