Multiparameter Elastic Full Waveform Inversion of Ocean Bottom Seismic Four-Component Data Based on A Modified Acoustic-Elastic Coupled Equation
Round 1
Reviewer 1 Report
Dear authors,
The paper is well written. I have several minor comments on your paper:
- You can probably do some sort of variable substitution for equation 8, for instance, q = (lambda + mu) p, sigma_n = mu tau_n, ..., which will make the system more like the forward system. It is also easier to derive an efficient FD scheme in this case, since in its original form (equation 8) you have to consider two partial derivative terms in the term such as \partial_x ( (lambda+mu) p), where one of them is the partial derivate of the medium parameter. Using variable substitution equation 10 can be simplified as well. But you can keep their current forms if you like. It is not mandatory.
- Give a brief discussion on the extra computational cost associated with PTGN. For example, its computational time compared with the modeling or gradient computation part.
- If possible please show the AEC equation in 3D in the appendix, for completeness purpose.
Good luck.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
I have attached the pdf file which includes my comments and suggestion for authors
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Thank you for your interesting paper. I suggest a minor revision, in the following, the issues that I noticed:
1. The authors mention a generic reduced computational cost. Please be more specific about it, and give magnitude order of computational cost. It is well known that elastic inversion is much more computationally expensive than acoustic, so the computational cost is a relevant issue for elastic FWI.
2. In the discussion, the authors suggest to use elastic inversion with 1C streamer data. In this scenario I expect to have small sensitivity on Vs change (so not reliable Vs estimate). Can the authors comment on that? What is the energy of the converted waves compared to P-wave?
2bis. As extension to this question, do you have confidence in the retrieved Vs image to use Vp/Vs as a hydrocarbon indicator? Please show/comment on Vp/Vs outcomes.
3. Is the elastic FWI you propose robust with respect to noise: both coherent and incoherent? Please comment on that, and if possible, provide some data.
4. Please insert comments on possible extensions to 3D. Is it feasible computationally? what will be the work to be done on that regard, mathematically and computationally
5. Please highlight what is the improvement brought by the 3C elastic data comparing Fig 12 ab and Fig 17.
6. Please show the wavelet spectrum. In particular, the content in low frequency. It gives indication on the amount of low frequencies which are propagated in the inversion. In fact, a well-known problem in inversion arises when the low frequencies are missing. In the manuscript the authors mention only the peak frequency 8 Hz and not the bandwidth. Please add it.
7. Minor spelling issues, such as “as same as”, “high-precise”, etc.. double check the language.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
See attached file
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 4 Report
Dear Authors,
The paper was improved following the main suggestions of the reviewers.
Some minor revisions of the paper are still necessary before publication in MDPI (Remote Sensing).
The remarks are listed here:
1) Authors used α and β for P- and S-wave velocities (eq. 11 and 12), however just below (equations 16 and 17) authors used VP and VS, as in all the paper and Figures. For coherency, the use of the same notations will be welcome: α and β or VP and VS, in all the paper. Add this modification in the paper.
2) In the response (point 1b, p2) authors listed the following papers, essentials for FWI multi-parameter inversion of multi-component data, however, these papers are missing in the list of references.
All relevant references mentioned in the answer of the authors need to be added in the "References" section:
Gholami Y, Brossier R, Operto S, Prieux V, Ribodetti A and Virieux J 2013a Which parameterization is suitable for acoustic vertical transverse isotropic full waveform inversion?I. Sensitivity and trade-off analysis Geophysics 78 R81–105.
Gholami Y, Brossier R, Operto S, Prieux V, Ribodetti A and Virieux J 2013b Which parameterization is suitable for acoustic vertical transverse isotropic full waveform inversion?II. Synthetic and real data case studies from Valhall Geophysics 78 R107–24.
Prieux V, Brossier R, Operto S and Virieux J 2013a Multiparameter full waveform inversion of multicomponent ocean-bottom-cable data from the Valhall field: I. Imaging compressional wave speed, density and attenuation Geophys. J. Int. 194 1640–64.
Prieux V, Brossier R, Operto S and Virieux J 2013b Multiparameter full waveform inversion of multicomponent ocean-bottom-cable data from the Valhall field: II. Imaging compressive-wave and shear-wave velocities Geophys. J. Int. 194 1665–81
Author Response
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Author Response File: Author Response.pdf
