Events of 2020 and before

• January 23rd 2019: Serge Sambolian received the AGU Outstanding Student Presentation Award (OSPA) granted to the top 5% of student participants of the AGU Fall meeting. * November 19th 2019: the Editorial Board of Geophysical Journal International has selected Serge Sambolian as the joint recipient of the 2019 GJI Student Author Award for his article “ Parsimonious slope tomography based on eikonal solvers and the adjoint-state method” (S Sambolian, S Operto, A Ribodetti, B Tavakoli and J Virieux; Geophys.J.Int. (2019) 218, 456-478)

• December 15th 2019: H. Aghamiry, A. Gholami and S. Operto submitted the abstract entitled Robust Full Waveform Inversion for sparse ultra-long offset OBN data to the EAGE Seabed Seismic Today: From Acquisition to Application workshop.

• December 18th 2019: H. Aghamiry defended his PhD thesis entitled "Multi-parameter Wavefield Reconstruction Inversion with the Alternating-Direction Method of Multipliers (ADMM) and Compound Regularization" at University of Tehran. This thesis has been performed in the framework of a co-supervizion agreement between University of Tehran and University of Nice-Sophia Antipolis.

• January 6th 2020: L. Combe joins the WIND project as a permanent CNRS HPC engineer. L. Combe will supervize the development of the time-domain and frequency-domain FWI codes developed during WIND.
• January 15th 2020: The WIND team submitted the following abstracts to the annual EAGE meeting

1 H. Aghamiry, A. Gholami and S. Operto, Wavefield inversion with adaptive regularization .

2 H. Aghamiry, A. Gholami and S. Operto, On the robustness of sparsity-promoting regularized wavefield inversion with phase retrieval against coarse sampling of sources and receivers .

3 H. Aghamiry, A. Gholami and S. Operto, Computationally-efficient frequency-domain wavefield reconstruction inversion with direct solver .

4 H. Aghamiry, A. Gholami and S. Operto, Proximal-Newton methods to solve non-linear problems with non-smooth regularization .

5 V. Dolean, P. Jolivet, P.-H. Tournier and S. Operto, Iterative frequency-domain seismic wave solvers based on multi-level domain-decomposition preconditioner.

• January 27th 2020: H. Aghamiry, A. Gholami and S. Operto submitted the masnuscript entitled "Full Waveform Inversion with Adaptive Regularization" to the Geophysical Journal International. This paper discusses two algorithms to implement non smooth and adaptive regularizations in nonlinear inverse problem such as FWI through proximal Newton optimization. The first algorithm relies on FISTA, while the second one relies on the alternating-direction method of multipliers (ADMM).

• February 3rd 2020: Frichnel-Wilma Mamfoumbi-Ozoumet started her PhD on frequency-domain FWI for long-offset node data. The main objective of this PhD is to assess the robustness of wavefield reconstruction inversion (WRI) and leading-edge regularization techniques as those developed by H. Aghamiry and A. Gholami these last two years against challenging ultra-long offset data sets starting from crude initial models. At least two case studies are targeted: the first is based upon the 2D SFJ OBN data set collected offshore the eastern Nankai trough (offshore Japan). The second relies on a 3D OBC dataset collected in the North Sea. In the first case, the goal is to check whether we can use a less accurate velocity model and a simpler workflow than those designed by Gorszczyk et al., 2017 to reach equivalent results. In the second case, the goal is to start from a basic velocity gradient model and assess also the improvement provided by sparsity promoting regularization to improve the results of Operto & Miniussi, 2018. Subsampled version of this OBC data set will be also used to assess to which extent sparsity-promoting regularization helps to mitigate the detrimental aliasing effects and low fold coverage. This will also used to assess the scheduled theoretical and numerical analysis of node acquisition design recast as an optimization problem.

• March 5th 2020: New codes are provided in the sponsor area: 1 FDFDMATRIX package generates an impedance matrix for 3D frequency-domain seismic wave modelling in visco-acoustic VTI media with the method of Operto et al. (2014). A smple code calling the MUMPS sparse direct solver can be used to check the wavefield solution. 1 Two toy codes test the FISTA and ADMM based regularization methods for nonlinear optimization problem developed in Full Waveform Inversion with Adaptive Regularization by Aghamiry et al., submitted to IEEE Transactions on Computational Imaging (preprint available in the sponsor area). We use the Rosenbrock function for this assessment.

• Schedule of the WIND presentations at the next EAGE meeting

1 V. Dolean, P. Jolivet, P.-H. Tournier and S. Operto. Iterative frequency-domain seismic wave solvers based on multi-level domain-decomposition preconditioners, Paper number 1328, Oral presentation, Wave Field Modelling 1, Tuesday, Jun 9, 2020, 8:30 AM - 12:10 PM, E104.

2 H. Aghamiry, A. Gholami, and S. Operto. Proximal-Newton methods to solve non-linear problems with non-smooth regularizations , Paper number 1801, ePoster: FWI B, Tuesday, Jun 9, 2020, 1:30 PM - 5:10 PM, ePosters 02.

3 H. Aghamiry, A. Gholami, and S. Operto. Computationally-efficient frequency-domain wavefield reconstruction inversion with direct solver , Paper number 1844, Oral presentation, FWI 1 - Cycle Skipping & Others, Wednesday, Jun 10, 2020, 8:30 AM - 12:10 PM, E102.

4 H. Aghamiry, A. Gholami, and S. Operto. Wavefield inversion with adaptive regularization , Paper number 1903, Oral presentation, FWI 3 - Regularization & Workflow, Thursday, Jun 11, 2020, 8:30 AM - 12:10 PM E102.

5 H. Aghamiry, A. Gholami, and S. Operto. On the robustness of sparsity-promoting regularized wavefield inversion with phase retrieval against sparse long-offset acquisitions , Paper number 1479, FWI 3 - Regularization & Workflow, Thursday, Jun 11, 2020, 8:30 AM - 12:10 PM, E102. Let's hopefully meet in December.

• April 15th 2020 The WIND team submitted the following abstracts to the annual SEG meeting

1 H. Aghamiry, A. Gholami and S. Operto, Simultaneous wavespeed and attenuation reconstruction with adaptive BM3D by complex-valued optimization regularization.

2 H. Aghamiry, A. Gholami and S. Operto, Wavefield inversion for microseismic imaging. 1 S. Sambolian, S. Operto, A. Ribodetti and L. Combe, From slope tomography to FWI: is the conventional workflow viable in complex settings?

3 S. Sambolian, S. Operto, A. Ribodetti, and J. Virieux, Revisiting the hypocenter-velocity problem through a slope tomography inspiration

4 V. Dolean, P. H. Tournier, P. Jolivet, and S. Operto, Large-scale frequency-domain seismic wave modeling on h-adaptive tetrahedral meshes with iterative solver and multi-level domain-decomposition preconditioners In the abstract 1, H. Aghamiry formulates visco-acoustic wavefield reconstruction inversion (WRI) with the alternating-method of multipliers (ADMM) in the complex field, namely the optimization parameter is the complex-valued velocity. An adaptive regularization operates also directly on the complex-valued velocity with the 3D block-matching filtering method BM3D. This approach implies that the inversion does not require a priori mathematical attenuation model as the Kolsky-Futterman model. Instead, the real phase velocity and the attenuation (or Q factor) are extracted a posteriori with arbitrary model of complex velocity. We explain how dispersion effects are taken into account during inversion. In the abstract 2, H. Aghamiry tackles the microseismic imaging problem in a FWI framework. He jointly update the wavefield, the source and the velocity model with ADMM-based WRI with appropriate sparsifying regularizations tailored to the last two variables (source and velocity model). No prior assumption on the number of events is made. In the abstract 3, S. Sambolian assesses whether a workflow combining first-arrival slope tomography and a brute-force FWI can reconstruct a complex model such as the original 2004 BP salt model (without rescaling) from an ultra-long offset (97km maximum offset) sparse OBN survey assuming a starting frequency of 1.5 Hz. The results are promising (the salt bodies are fully captured, subsalt imaging is more challenging). Improvement should come from feeding slope tomography with short-spread and post-critical reflections in addition to the first arrivals to supplement these latters in complex or poorly-illuminated area and by equipping FWI with sparsifying regularization as those developed by H. Aghamiry. Ongoing work... In the abstract 4, S. Sambolian tackles the hypocenter-velocity problem with a slope tomography inspiration. This supplements the abstract 2 with a ray-theory based approach. In the abstract 5, V. Dolean, P. H. Tournier and P. Jolivet revisit the results of the EAGE abstract dealing with frequency-domain seismic wave modeling on tetrahedral meshes with ORAS domain-decompositon preconditioners. They investigate which Lagrange polynomials should be used to achieve a sufficient accuracy for a discretization rule of 4-5 grid points per wavelength. They also clarify which backward error tolerance should be used to get accurate wavefield solution, while minimzing the iteration count. They test whether single precision arithmetic provides accurate solution, compare the performance and accuracy of the preconditioner when Cholesky and incomplete LU factorization are used to solve the local problems, and assess the potential of a second level of preconditioning on a coarse grid. The preprint of these abstracts are available on the sponsor page.

• April 16th 2020: Matlab codes developed by Hossein Aghamiry are provided in the sponsor page to practice various implementations of IR-WRI.

• May 8th 2020: The WIND technical report n°1 entitled "A practical guide to implement smooth and nonsmooth regularization in Full Waveform Inversion with ADMM" is provided in the sponsor area. This technical report describes a generic procedure based on the alternating-direction method of multiplier (ADMM) to implement smooth and nonsmooth regularization in classical FWI. We review a vast catalog of regularizers including bound constraints, Tikhonov regularizer, Total-Variation (TV) regularizer, compound regularizer such as the Total Generalized Variation regularizer (TGV).

• May 29th 2020: Hossein Aghamiry submitted the paper entitled "Full Waveform Inversion by Proximal Newton Method using Adaptive Regularization" to the Geophysical Journal International. The preprint is provided on the sponsor page.

• June 14th 2020: Hossein Aghamiry submitted the paper entitled "Complex-valued Imaging with Total Variation Regularization: An Application to Full-Waveform Inversion in Visco-acoustic Media" to the SIAM Journal on Imaging Science. The preprint is provided on the sponsor page.

• June 22th 2020: The SEG abstracts submitted by the WIND group (see the list above) are accepted for presentation.

• June 25th 2020: The WIND Kick-off meeting will be held on Tuesday June 30 and Wednesday July 1st by visio conference.

• June 25th 2020: A new release of the Matlab codes developed by Hossein Aghamiry are provided on the sponsor page.

• June 26th 2020: The massively-parallel 2D/3D time-domain FWI code Geoinv3D_fwk have been uploaded on the sponsor page by L. Combe. The platform will be used to test the concepts developed during the WIND project on large-scale synthetic and real case studies.

• June 28th 2020: The presentations of the Kick-off meeting have been uploaded in the sponsor page.

• August 4th 2020: the preprint of the publication On efficient frequency-domain full-waveform inversion with extended search space submitted by H. Aghamiry, A. Gholami and S. Operto to Geophysics has been uploaded on the sponsor page.

• August 4th 2020: the preprint of the publication Consistent seismic event location and subsurface parameters inversion through slope tomography: a variable-projection approach submitted by S. Sambolian, S. Operto, A. Ribodetti and J. Virieux to the Geophyslcal Journal International has been uploaded on the sponsor page.

• September 10th: S. Operto gave a presentation co-authored with H. Aghamiry and A. Gholami at the EAGE workshop EAGE Seabed Seismic Today: Acquisition to Application (https://eage.eventsair.com/seabed-seismic-ws). The talk was entitled: Robust Full Waveform Inversion for sparse ultra-long offset OBN data.

• October 1st 2020: Sebastian Riffo joined the WIND staff as a postdoc. He will work on Helmholtz problem with the ORAS method in collaboration with V. Dolean, P. Jolivet and P.H. Tournier and its interfacing with WRI codes. Sebastian Riffo has a background in applied mathematics, in particular on optimization, data assimilation and domain decomposition methods.

• October 12th 2020: The paper entitled "Complex-valued imaging with total variation regularization: an application to full-waveform inversion in visco-acoustic media" by H. Aghamiry, A. Gholami and S. Operto is accepted for publication in "SIAM Journal on Imaging Sciences".

• November 2nd 2020: The SEG presentations of the WIND team are available on the intranet page for sponsors.

• November 2nd 2020: The 2020 activity report of the WIND project is available on the intranet page for sponsors.

• November 25th 2020: The paper entitled "Consistent event location and subsurface parameters inversion through slope tomography: a variable projection approach" by S. Sambolian, S. Operto, A. Ribodetti and J. Virieux is accepted for publication in the Geophysical Journal International.

• November 25th 2020: The paper entitled "On efficient frequency-domain Full-Waveform Inversion with extended search space" by H. Aghamiry, A. Gholami and S. Operto is accepted for publication in Geophysics. The last versions have been uploaded in the sponsor page.

• December 7th 2020: The final version of "Full Waveform Inversion by Proximal Newton Method using Adaptive Regularization" is published in the Geophysical Journal International. The PDF is available on the sponsor page.