Article (Scientific journals)
Deep generative models in inversion: The impact of the generator's nonlinearity and development of a new approach based on a variational autoencoder
Lopez-Alvis, Jorge; Laloy, Eric; Nguyen, Frédéric et al.
2021In Computers and Geosciences, 152, p. 104762
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Keywords :
Deep generative model; Deep learning; Geological prior information; Geophysical inversion; Stochastic gradient descent; Variational autoencoder; Conceptual frameworks; Generative functions; Geological setting; Geophysical imaging; Gradient-based method; Markov Chain Monte-Carlo; Training parameters; Information Systems; Computers in Earth Sciences
Abstract :
[en] When solving inverse problems in geophysical imaging, deep generative models (DGMs) may be used to enforce the solution to display highly structured spatial patterns which are supported by independent information (e.g. the geological setting) of the subsurface. In such case, inversion may be formulated in a latent space where a low-dimensional parameterization of the patterns is defined and where Markov chain Monte Carlo or gradient-based methods may be applied. However, the generative mapping between the latent and the original (pixel) representations is usually highly nonlinear which may cause some difficulties for inversion, especially for gradient-based methods. In this contribution we review the conceptual framework of inversion with DGMs and propose that this nonlinearity is caused mainly by changes in topology and curvature induced by the generative function. As a result, we identify a conflict between two goals: the accuracy of the generated patterns and the feasibility of gradient-based inversion. In addition, we show how some of the training parameters of a variational autoencoder, which is a particular instance of a DGM, may be chosen so that a tradeoff between these two goals is achieved and acceptable inversion results are obtained with a stochastic gradient-descent scheme. A series of test cases using synthetic models with channel patterns of different complexity and cross-borehole traveltime tomographic data involving both a linear and a nonlinear forward operator show that the proposed method provides useful results and performs better compared to previous approaches using DGMs with gradient-based inversion.
Disciplines :
Geological, petroleum & mining engineering
Author, co-author :
Lopez-Alvis, Jorge ;  Urban and Environmental Engineering, Applied Geophysics, University of Liège, Belgium ; Department of Geology, Ghent University, Belgium
Laloy, Eric;  Engineered and Geosystems Analysis, Institute for Environment, Health and Safety, Belgian Nuclear Research Center, Belgium
Nguyen, Frédéric ;  Université de Liège - ULiège > Département ArGEnCo > Géophysique appliquée
Hermans, Thomas;  Department of Geology, Ghent University, Belgium
Language :
English
Title :
Deep generative models in inversion: The impact of the generator's nonlinearity and development of a new approach based on a variational autoencoder
Publication date :
July 2021
Journal title :
Computers and Geosciences
ISSN :
0098-3004
Publisher :
Elsevier Ltd
Volume :
152
Pages :
104762
Peer reviewed :
Peer Reviewed verified by ORBi
European Projects :
H2020 - 722028 - ENIGMA - European training Network for In situ imaGing of dynaMic processes in heterogeneous subsurfAce environments
Funders :
EU - European Union [BE]
Funding text :
This work has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement number 722028 (ENIGMA ITN). We thank the anonymous reviewers and the editor for their valuable comments that greatly improved the manuscript.
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