A New Method for InSAR Stratified Tropospheric Delay Correction Facilitating Refinement of Coseismic Displacement Fields of Small-to-Moderate Earthquakes

Round 1

Reviewer 1 Report

In this study, the authors present a simple stratification correction approach based on the empirical phase-elevation relationship and spatial properties of the troposphere, via an equal-size window segmentation. I think this method is very relevant as it has broad implications to several disciplines. 

I have provided a list of minor comments (and references missing), which I hope the authors can address. That said, I would mark this review as "minor". If the authors address my comments properly, I would be happy to recommend publication of this manuscript.

• Tropospheric delays in differential interferometric synthetic aperture radar (InSAR) measurements are mainly caused by spatial and temporal variation of pressure, temperature, and humidity between SAR acquisitions. These delays are described as one of the primary error sources in InSAR observations. In particular, the performance of the conventional phase-based correction method is weakened by the presence of confounding signals (e.g. topographic errors) and spatial variability of the troposphere. Do the authors think you can link the parameters of deformation (for example, during an earthquake) and topographic error based on their distinct spatial-temporal correlation? For example, with the approach proposed, can the authors use localized estimation in windows divided by quadtree according to height gradient?

Here some references to add:

+ Jolivet, R., Agram, P. S., Lin, N. Y., Simons, M., Doin, M. P., Peltzer, G., & Li, Z. (2014). Improving InSAR geodesy using global atmospheric models. Journal of Geophysical Research: Solid Earth, 119(3), 2324-2341.

+ Lauknes, T. R. (2011). InSAR tropospheric stratification delays: Correction using a small baseline approach. IEEE Geoscience and Remote Sensing Letters, 8(6), 1070-1074.

• The authors used this new correction for the coseismic displacement of earthquakes. As indicated by e.g. (already cited):

+ Elliott, J. R., R. J. Walters, and T. J. Wright. "The role of space-based observation in understanding and responding to active tectonics and earthquakes." Nature communications 7, no. 1 (2016): 1-16.

• A disadvantage of InSAR is the repeat time of satellite passes, resulting in some postseismic deformation being captured with the coseismic signal. Of course, this problem will be reduced with the shorter revisit times by an increasing number of radar satellite constellations, but very rapid fault afterslip will still be incorporated into such measurements. Do the authors think that their method can be valid during the post-seismic and interseismic phases of tectonic faults? 

+ Dal Zilio, L., Jolivet, R., & van Dinther, Y. (2020). Segmentation of the Main Himalayan Thrust illuminated by Bayesian inference of interseismic coupling. Geophysical Research Letters, 47(4)

+ Grandin, R., Doin, M. P., Bollinger, L., Pinel-Puysségur, B. (2012). Long-term growth of the Himalaya inferred from interseismic InSAR measurement. Geology, 40(12), 1059-1062.

• This is a significant advancement because short-period interferograms better maintain coherence and can capture time-dependent deformation, as well as provide a greater number of sampling observations to reduce atmospheric noise in measuring small strain accumulation. This is a very important point because it can have broad implication in the segmentation of large faults, interseismic coupling, and long-term (geologic deformation):

+ Dal Zilio, L., Hetényi, G., Hubbard, J. (2021). Building the Himalaya from tectonic to earthquake scales. Nature Reviews. 2(4), 251-268.

With the proposed method, a proper mask is necessary to exclude impacts from the co-seismic signal in the tropospheric phase modeling, which can reduce the bias from co-seismic displacement signals. A single interferogram can keep better coherence with the available shortest temporal baseline. However, I wonder if this might be a problem for longer time series, particularly in case you are trying to assess the long-term fault slip. I encourage the authors to discuss further whether this is a problem or not, as it has very broad implication for the assessment of the moment budget on active fauts:

+ Michel, S., Jolivet, R., Rollins, C. (2021). Seismogenic potential of the Main Himalayan Thrust constrained by coupling segmentation and earthquake scaling. Geophysical Research Letters, 48(13).

 

 

Author Response

Dear Reviewers,

First of all, we thank you very much for facilitating the last review of the manuscript. We appreciate the reviewers and the editorial board for their valuable input and for taking the time to review this paper. After revision, we resubmit our revised manuscript for publication in Remote Sensing. It includes a revised manuscript, a supplementary file and a response letter. In the revised manuscript, all corrections have been highlighted for the reviewers’ reference.

The main overall changes are as follows:

1. We provided more details and discussion about the using power-law model in our developed atmospheric correction method.
2. We provide more details of estimating Scale and Offset parameter maps when using linear phase-elevation model in our new method.

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript.

Sincerely,

 

Wenyu Gong

March 2022

Institute of Geology, China Earthquake Administration

Author Response File: Author Response.docx

Reviewer 2 Report

See attachment. 

Comments for author File: Comments.pdf

Author Response

Dear Reviewers,

First of all, we thank you very much for facilitating the last review of the manuscript. We appreciate the reviewers and the editorial board for their valuable input and for taking the time to review this paper. After revision, we resubmit our revised manuscript for publication in Remote Sensing. It includes a revised manuscript, a supplementary file and a response letter. In the revised manuscript, all corrections have been highlighted for the reviewers’ reference.

The main overall changes are as follows:

1. We provided more details and discussion about the using power-law model in our developed atmospheric correction method.
2. We provide more details of estimating Scale and Offset parameter maps when using linear phase-elevation model in our new method.

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript.

Sincerely,

 

Wenyu Gong

March 2022

Institute of Geology, China Earthquake Administration

Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors,

Please see the attached file for minor text corrections.

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewers,

First of all, we thank you very much for facilitating the last review of the manuscript. We appreciate the reviewers and the editorial board for their valuable input and for taking the time to review this paper. After revision, we resubmit our revised manuscript for publication in Remote Sensing. It includes a revised manuscript, a supplementary file and a response letter. In the revised manuscript, all corrections have been highlighted for the reviewers’ reference.

The main overall changes are as follows:

1. We provided more details and discussion about the using power-law model in our developed atmospheric correction method.
2. We provide more details of estimating Scale and Offset parameter maps when using linear phase-elevation model in our new method.

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript.

Sincerely,

 

Wenyu Gong

March 2022

Institute of Geology, China Earthquake Administration

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have done an excellent job in addressing all my comments on the previous version. I am now happy to recommend acceptance of this manuscript.