Marchenko focusing for target-oriented data processing and full-waveform inversion

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Author
Date
2020Type
- Doctoral Thesis
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Abstract
Measuring wave motion on the surface of an unknown medium can help us infer the physical properties of the medium through which waves propagate without intrusion. In many applications,
multiple scattering and high computational cost prevent state-of-the-art data processing
techniques from delivering a high-quality image of the medium, especially when it is complex.
The recently developed Marchenko focusing technique has potential to overcome these challenges
by performing data processing and imaging in a target-oriented fashion. Superior to conventional
redatuming methods, Marchenko focusing retrieves multiply-scattered waves from single-sided
reflection data with minimal a priori knowledge of medium properties. By iteratively re-emitting
a time-reversed and time-windowed wavefield from a single side of the unknown medium, we
can focus the wavefield at a prescribed virtual source position inside the medium. The redatumed
wavefields in response to the virtual source can be used for imaging free from artefacts related to
multiple scattering and interference from the medium surrounding the target.
In this thesis, I work on practical implementation and applications of the Marchenko focusing technique.
I first review the theory and methodology of the standard Marchenko scheme using 1D and
2D acoustic numerical examples. Then, I investigate its potential application to the hDVS (heterodyne
distributed vibration sensing) technology, which records wavefields semi-continuously in
space using an optical fibre. The hDVS signal is focused by the Marchenko method in the optical
frequency regime, based on an analytical hDVS model. With a hypothesis of strong scattering
inside the fibre, the redatumed hDVS signal may contribute to improving strain estimation. Next,
I implement Marchenko focusing in a dissipative medium by both numerical modelling and laboratory
implementation. To accommodate dissipation which is not accounted for in the standard
Marchenko scheme, double-sided reflection data are required to derive an effectual reflection
response. Physical focusing of the sound wave is achieved in a 1D variable-diameter tube. Finally,
I conduct target-oriented FWI (full-waveform inversion) by using Marchenko focusing to
extrapolate the wavefields from the acquisition surface to the vicinity of the target. Based on the
representation theorem of the convolution type, a local forward modelling operator couples the
target and the surrounding medium acoustically. I invert for the optimal target model, whose
seismic response to the Marchenko retrieved areal sources best matches the Marchenko retrieved
observed data. Given a sufficiently accurate initial velocity model, local FWI saves computational cost by a factor of ten in a 2D numerical test without sacrificing accuracy compared to conventional
full-domain FWI. This thesis further establishes the applicability of Marchenko focusing to
better characterize the physical properties of the medium of interest. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000423475Publication status
publishedExternal links
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Contributors
Examiner: Robertsson, Johan O.A.
Examiner: van Manen, Dirk-Jan
Examiner: Rickett, James E.
Examiner: Vasconcelos, Ivan
Examiner: Meles, Giovanni A.
Publisher
ETH ZurichSubject
Geophysics; Seismic interferometry; Waveform inversionOrganisational unit
03953 - Robertsson, Johan / Robertsson, Johan
Funding
641943 - Waves and Wave-Based Imaging in Virtual and Experimental Environments (SBFI)
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