Full waveform inversion(FWI)is a data-fitting inverse problem aiming to delineate high-resolution quantitative images of the Earth.While its basic principle has been proposed in the eighties,the approach has been sign...Full waveform inversion(FWI)is a data-fitting inverse problem aiming to delineate high-resolution quantitative images of the Earth.While its basic principle has been proposed in the eighties,the approach has been significantly developed and applied to2Dand 3Dproblems at various scales for the last fifteen years.Despite these successes,FWI is still facing some issues for applications in complex geological setups because of some lack of robustness and automatic workflow,while being computationally intensive.In this paper,after a short review of the basic FWI formulation and analysis of the FWI gradient,three recent methodological developments performed in the frame of the SEISCOPE project are presented.First,an algorithmic development is presented as a low-memory and computationally efficient approach for building the time-domain FWI gradient in 3Dviscous media.Second,a reformulation of FWI is performed to handle reflections in their tomography regime while still using the diving waves,leading to the joint full waveform inversion(JFWI)approach.Finally,an optimal transport approach is proposed as an alternative to the classical difference-based misfit for mitigating the cycle-skipping issue.展开更多
We use the first arrival traveltime to correct the phase distortion in a nonlinear wave equation inversion scheme.This improves the precision of tomographic reconstruction of a velocity structure with large variations...We use the first arrival traveltime to correct the phase distortion in a nonlinear wave equation inversion scheme.This improves the precision of tomographic reconstruction of a velocity structure with large variations and helps solve the ill-posed problem of wave equation inversion.When the variation of the velocity distribution is large,general non-linear wave equation inversions are very ill-posed and for such strong nonlinear we can not obtain a correct inversion.One of main reasons is that the calculated and observed phase of the wavefield differs greatly if the initial model is far from the true model.This leads to highly mismatched phase between the calculated and the observed wave field.This is so-called"Cycle Skipping"problem in the full waveform inversion.The phase mismatch is even more pronounced if a high operating frequency is employed in order to increase resolution.To address this problem,we use the first arrival to"demodulate"the wave field in the frequency domain with a goal of restoring the phase of wave field.Then we minimize an objective function consisting of so called"demodulated"wave field to solve wave equation inversion problem.In this way,we find that the inversion is much improved,and when the velocity perturbation in a complicated model reaches 35%,we can still obtain a good inversion.A computer simulation shows that our method is very robust for acoustical wave inversion with good reconstruction precision.展开更多
The first-arrival traveltime tomography is a standard approach for near-surface velocity estimation.However,it cannot resolve complex near-surface structures and will produce a smooth velocity model with low resolutio...The first-arrival traveltime tomography is a standard approach for near-surface velocity estimation.However,it cannot resolve complex near-surface structures and will produce a smooth velocity model with low resolution.Early arrival waveform inversion is a robust tool for imaging the near surface structures,but it requires a good initial model to avoid cycle skipping between the predicted and observed data.Furthermore,waveform inversion requires substantial computation efforts.Therefore,we present joint seismic traveltime and waveform inversion method,and we expect the joint inversion method retains the advantages of both traveltime inversion and full waveform inversion and overcomes their respective drawbacks at the same time.The objective function includes both the traveltime and waveform misfit.At each iteration,the traveltimes are calculated by wavefront raytracing,and the waveforms are computed using a finite-difference method.The nonlinear optimization problem is solved by the conjugate gradient method.We apply the joint inversion method to study complex near-surface area where shallow overthrust and rugged topography present a significant challenge for applying traveltime inversion and waveform inversion alone.We test synthetic data to verify the advantages of the joint method,and then apply the method to a 2Ddataset acquired in Yumen Oil field,China.The inversion results suggest that the joint traveltime and waveform inversion helps constrain the very shallow velocity structures and also resolve complex overthrust with large velocity contrasts.展开更多
Objective To investigate the clinical application value of Loewenstein Occupational Therapy Cognitive Assessment （LOTCA） battery in Chinese patients with post-stroke aphasia. Methods Cognitive fimctions of 59 Chine...Objective To investigate the clinical application value of Loewenstein Occupational Therapy Cognitive Assessment （LOTCA） battery in Chinese patients with post-stroke aphasia. Methods Cognitive fimctions of 59 Chinese patients with aphasia following a stroke were assessed with the Chinese version of the second edition of LOTCA battery and their linguistic functions were tested with the Western Aphasia Battery （WAB） Scale, respectively. The results of LOTCA were analyzed and compared across different groups, in the light of gender, age, educational background, the length of illness, and the degree of aphasia.展开更多
基金funded by the SEISCOPE consortium (http:∥ seiscope2.osug.fr)sponsored by CGG,CHEVRON,EXXON-MOBIL,JGI,SHELL, SINOPEC,STATOIL,TOTAL and WOODSIDEgranted access to the HPC resources of the Froggy platform of the CIMENT infrastructure (https:∥ ciment.ujf-grenoble.fr), which is supported by the Rh8ne-Alpes region (GRANT CPER07_13 CIRA)+2 种基金the OSUG@2020 labex(reference ANR10LABX56)the Equip@Meso project (reference ANR-10-EQPX-29-01)of the programme Investissements d'Avenir supervised by the Agence Nationale pour la Recherchethe HPC resources of CINES/IDRIS under the allocation 046091made by GENCI
文摘Full waveform inversion(FWI)is a data-fitting inverse problem aiming to delineate high-resolution quantitative images of the Earth.While its basic principle has been proposed in the eighties,the approach has been significantly developed and applied to2Dand 3Dproblems at various scales for the last fifteen years.Despite these successes,FWI is still facing some issues for applications in complex geological setups because of some lack of robustness and automatic workflow,while being computationally intensive.In this paper,after a short review of the basic FWI formulation and analysis of the FWI gradient,three recent methodological developments performed in the frame of the SEISCOPE project are presented.First,an algorithmic development is presented as a low-memory and computationally efficient approach for building the time-domain FWI gradient in 3Dviscous media.Second,a reformulation of FWI is performed to handle reflections in their tomography regime while still using the diving waves,leading to the joint full waveform inversion(JFWI)approach.Finally,an optimal transport approach is proposed as an alternative to the classical difference-based misfit for mitigating the cycle-skipping issue.
基金supported by the Seismic Tomography Project of Stanford University,a research consortium sponsored by companies of the oil and gas industry
文摘We use the first arrival traveltime to correct the phase distortion in a nonlinear wave equation inversion scheme.This improves the precision of tomographic reconstruction of a velocity structure with large variations and helps solve the ill-posed problem of wave equation inversion.When the variation of the velocity distribution is large,general non-linear wave equation inversions are very ill-posed and for such strong nonlinear we can not obtain a correct inversion.One of main reasons is that the calculated and observed phase of the wavefield differs greatly if the initial model is far from the true model.This leads to highly mismatched phase between the calculated and the observed wave field.This is so-called"Cycle Skipping"problem in the full waveform inversion.The phase mismatch is even more pronounced if a high operating frequency is employed in order to increase resolution.To address this problem,we use the first arrival to"demodulate"the wave field in the frequency domain with a goal of restoring the phase of wave field.Then we minimize an objective function consisting of so called"demodulated"wave field to solve wave equation inversion problem.In this way,we find that the inversion is much improved,and when the velocity perturbation in a complicated model reaches 35%,we can still obtain a good inversion.A computer simulation shows that our method is very robust for acoustical wave inversion with good reconstruction precision.
基金the financial support of the National Natural Science Foundation of China (Grant No.41374132 and No.41674120)
文摘The first-arrival traveltime tomography is a standard approach for near-surface velocity estimation.However,it cannot resolve complex near-surface structures and will produce a smooth velocity model with low resolution.Early arrival waveform inversion is a robust tool for imaging the near surface structures,but it requires a good initial model to avoid cycle skipping between the predicted and observed data.Furthermore,waveform inversion requires substantial computation efforts.Therefore,we present joint seismic traveltime and waveform inversion method,and we expect the joint inversion method retains the advantages of both traveltime inversion and full waveform inversion and overcomes their respective drawbacks at the same time.The objective function includes both the traveltime and waveform misfit.At each iteration,the traveltimes are calculated by wavefront raytracing,and the waveforms are computed using a finite-difference method.The nonlinear optimization problem is solved by the conjugate gradient method.We apply the joint inversion method to study complex near-surface area where shallow overthrust and rugged topography present a significant challenge for applying traveltime inversion and waveform inversion alone.We test synthetic data to verify the advantages of the joint method,and then apply the method to a 2Ddataset acquired in Yumen Oil field,China.The inversion results suggest that the joint traveltime and waveform inversion helps constrain the very shallow velocity structures and also resolve complex overthrust with large velocity contrasts.
文摘Objective To investigate the clinical application value of Loewenstein Occupational Therapy Cognitive Assessment （LOTCA） battery in Chinese patients with post-stroke aphasia. Methods Cognitive fimctions of 59 Chinese patients with aphasia following a stroke were assessed with the Chinese version of the second edition of LOTCA battery and their linguistic functions were tested with the Western Aphasia Battery （WAB） Scale, respectively. The results of LOTCA were analyzed and compared across different groups, in the light of gender, age, educational background, the length of illness, and the degree of aphasia.
