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  Signal and noise in helioseismic holography

Gizon, L., Fournier, D., Yang, D., Birch, A., & Barucq, H. (2018). Signal and noise in helioseismic holography. Astronomy and Astrophysics, 620: A136. doi:10.1051/0004-6361/201833825.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0003-2AB0-7 Version Permalink: http://hdl.handle.net/21.11116/0000-0003-2AB1-6
Genre: Journal Article

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 Creators:
Gizon, Laurent1, Author              
Fournier, Damien1, Author              
Yang, Dan1, Author              
Birch, Aaron1, Author              
Barucq, Hélène, Author
Affiliations:
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              

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Free keywords: Sun: helioseismology / Sun: interior / Sun: oscillations
 Abstract: Context. Helioseismic holography is an imaging technique used to study heterogeneities and flows in the solar interior from observations of solar oscillations at the surface. Holographic images contain noise due to the stochastic nature of solar oscillations. Aims. We aim to provide a theoretical framework for modeling signal and noise in Porter–Bojarski helioseismic holography. Methods. The wave equation may be recast into a Helmholtz-like equation, so as to connect with the acoustics literature and define the holography Green’s function in a meaningful way. Sources of wave excitation are assumed to be stationary, horizontally homogeneous, and spatially uncorrelated. Using the first Born approximation we calculated holographic images in the presence of perturbations in sound-speed, density, flows, and source covariance, as well as the noise level as a function of position. This work is a direct extension of the methods used in time-distance helioseismology to model signal and noise. Results. To illustrate the theory, we compute the holographic image intensity numerically for a buried sound-speed perturbation at different depths in the solar interior. The reference Green’s function is obtained for a spherically-symmetric solar model using a finite-element solver in the frequency domain. Below the pupil area on the surface, we find that the spatial resolution of the holographic image intensity is very close to half the local wavelength. For a sound-speed perturbation of size comparable to the local spatial resolution, the signal-to-noise ratio is approximately constant with depth. Averaging the image intensity over a number N of frequencies above 3 mHz increases the signal-to-noise ratio by a factor nearly equal to the square root of N. This may not be the case at lower frequencies, where large variations in the holographic signal are due to the contributions from the long-lived modes of oscillation.

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Language(s): eng - English
 Dates: 2019-03-132018
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/201833825
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 620 Sequence Number: A136 Start / End Page: - Identifier: Other: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1