Explanation of InSAR Phase Disturbances by Seasonal Characteristics of Soil and Vegetation

Round 1

Reviewer 1 Report

The article presents interesting research and very well prepared. The test procedure is clear and justified. The study data are rightly chosen and sufficient. The authors of the article correctly described the study; it is important that the test procedure can be reproduced by other researchers. Text is written in a logical and thoughtful way, creating a coherent whole, in accordance with the writing regime of scientific paper (IMRaD). The method of presentation, comprehensive introduction and very interesting and thoughtful practical examples deserve praise. Authors did a very good job - the text reads very well, and I have no comments in terms of editing. Below are some remarks, after taking into account which text is suitable for a publication:

1) Some of references positions are missed e.g. [32], [33] and other

2) To many empty places in the text, e.g. Table 1, Figure 2, Figure 3 and other

3) there is now reference in the text to Figure 2, Figure 3 and Figure 4. It seems like these Figures might be deleted from the manuscript in it’s current form without loosing sense.

4) I am not not entirely convinced of 'Sumplementary materials' in its current form. It would be better to move it into the text in a logical way, or just refer to literature.

All the best

Author Response

Dear reviewer,

Thank you very much for your efforts, we consider your review a compliment to our work. In light of some of the other reviewer's comments we did decide to change the naming convention to a more standardised structure (Introduction, Material and Methods, Findings, Discussion, Conclusion). 

In light of your comments: 

1) This might be a question for typesetting more, but references 31-39 are in the supplement. We now put all the references (main document + supplement) in one References section. Please let us if the Supplement requires a separate References list.  

2) This is also a typesetting question. We will confer with typesetting on how to best place the tables and figures. For now, we followed the procedure of trying to put the figures and tables as close to the sections where they belong (for the LATEX experts under us: we used \clearpage to do that). However, we are happy to have the typesetting experts repair whatever is needed. 

3) I assume you mean 'there is NO reference in the text to Figure 2, 3 and 4'. There are, but they are called 'Fig.'. We corrected these 'Fig.' To 'Figure' (line 123, line 140, line 145 of original document). 

4) The reviewer has noticed well that the amount of theory in the main paper can be debated on. We chose an approach where we only show the main findings of our review of theory and put that into the main text; where all details that are needed to derive the equations in the main text are shared in the Supplementary Material. To address the reviewer's comments, we have now moved more (but not all) details that were originally provided in the Supplement. Including all details did deteriorate readability in our opinion, e.g., the remarks on coherence need to be given, but since they were hardly used to filter mentioning this in the main text deteriorates readability. We hope that our changes sufficiently address the reviewers comment. Additionally, these changes made have the additional benefit of better highlighting our original contribution to this study (a remark made by another reviewer).  

Kind regards

Reviewer 2 Report

Dear authors,

I read your paper with great interest. Even though this is a fairly 'academic' topic, I believe there is a place for it in the literature. I can vouch that it is one of the best I have reviewed lately, so kudos to you.

There are a few minor issues with its current state. First of all, the article can use a better organizing. Please update the section titles and use standard literature format I. Introduction II. Materials and methods III. Findings IV. Discussion V. Conclusion.

I have a few minor comments and I highlighted them all for your reference. Thank you for your contribution.

Regards

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for the valuable comments and hope we have addressed the accordingly.  

We have fixed the structure, putting both Theory and Methods in a 'Materials and Methods' section and changing 'Results' to 'Findings'. In 'Findings' we now have the two sub-sections 'Result analyses of our three experiments' and 'Comparison of our results to other studies'. 

See attached PDF for how we further addressed your other (valuable!) comments. 

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors attributed the seasonal phase changes to soil moisture and vegetation characteristics, rather than displacements. It remains unclear if the seasonal signals are actual displacement or soil and vegetation changes. It is interesting to see a dispute like this.

Author Response

We thank the reviewer for these comments. We assume no changes need to be made, nonetheless we did put some attention trying to clarify what next steps need to be to further explore and further prove or disprove our hypothesis. This is mainly in the earlier mentioned recommendation to combine the Study of De Zan et al with ours in future research. See section 'Findings', subsection 'Comparison of our results to other studies'. 

Reviewer 4 Report

The Interferometric Synthetic Aperture Radar (InSAR) technique has become widely applied for measuring land terrain motion, which has attracted growing interest in recent years. The authors focused on the issues of explanation and interpretation of the seasonal soil moisture and vegetation signatures. The idea is interesting and the paper is well constructed. Before possible publication, minor revision is recommended and the following points should be considered.

1. The description of the method is unclear and only 7 formulations are utilized which makes the readers difficult to follow. Most of these formulations, e. g., expression 1-7, are from cited publications. Thus is very hard to tell the contribution of the authors' work. The authors could pay more attention on the description of the method and further emphasize the contribution of their word.

2. In Section 5, the authors compared their method to other study and discuss the advantages of their method. If possible, the authors could conduct some simulations from other study to demonstrate the advantages of their method.

3. Most references are very old. Please pay more attention to state-of-art studies.

Author Response

We thank this reviewer for the compliment on structure. Alongside the comments of all reviewers (who all had minor revisions) we tried to incorporate your suggested revisions as: 

1. We tried to slightly adapt the structure so it becomes clearer what our original contribution is. Firstly, we added the theory as part of materials and methods (suggestion by another reviewer), yet making it very clear that the first theory sections outlines and combined earlier fundamental microwave radar physics theory. The second part, method, then clarifies that some of the equations in the theory were coded in a tailored way to output phase and amplitude after reflection (Exp I), transmission and reflection (exp II) and a realistic scenario (Exp II, 'year in a paddock'). However, we do want to stress that the original contribution of this study is that the experiments were devised in such a way that their findings provide an alternative explanation for seasonal signatures. Basically, 'fundamental science' already provides an explanation for LOS displacements of a non-moving surface and this might have been overlooked earlier. Additionally, we tried to better highlight our contribution by small changes, e.g.: i) highlighting that we modelled and we designed new experiments to better highlight focusing on what happens with phase disturbance; ii) further highlight in methods saying "We developed a model that calculates phase disturbances based on reflection and transmission of microwave waves, as described in Eqs. 4-7. This model was applied in three experiments ....etc .... " and "The model and all experiments were coded in the Matlab coding software, with all scripts available as open data (see supplementary material)." iii) at the start of the section 'Comparison to other studies'  from: "The results of this study  show....." to "The results of this study  reveal....."; or from "This confirms the finding..." to "This confirms our finding...."; highlighting the fact that we devised our experiment in such a way for this finding to be analysed from the resulting plots. 
2. In our comparison to other studies, we now go into a bit more detail of whether deformations found in other studies match those found with our study. For example, the study of Ozer et al shows the same pattern and magnitude of deformation as we model. To reflect this, we changed the text to "Ozer et al [14] interpret seasonally occurring phase differences and LOS displacements of levees of up to 1 cm as forthcoming from swelling and shrinkage behaviour, including an underlying deformation behaviour model. Our models find the same magnitude and seasonal pattern of deformation, suggestion that phase differences through soil moisture and vegetation characteristics can explain for their LOS displacement.". Conducting further experiments to match findings of Brancato, De Zan etc it is not feasible at this stage. That is partly because we don’t have the details of those experiments in our possession. Furthermore, the studies we mentioned focused on different aspects and on polarimetric SAR, which we did not include in our study. More importantly, in our opinion, conducting these experiments are best done with a more advanced model, e.g. from De Zan et al (2014).  However, if such a comparative study would be done, we would need to match DeZan's inversion from dielectric properties to soil moisture to our estimates of dielectric properties from soil moisture. However, since they do not include vegetation, the first recommendation given is to include the effects of vegetation in DeZan;'s study; and then continue using similar experiment set-ups, e.g. our I, II and III. Therefore, we give the important recommendation for further research to combine our finding with DeZan et al. 
3. In our new adjusted version, we added five more recent references, to better reflect the recent work of InSAR on earthquakes, volcanos, landslide, and hydrology. Our referenced InSAR studies are now from: 2004, 2010, 2011, 2014, 2016, 2017, 2018(3x), 2019(3x), which we hope is a nice enough spread of older and more recent InSAR studies. The point we make in 1) ( 'fundamental science' already provides an explanation for LOS displacements of a non-moving surface and this might have been overlooked earlier) also explains why some of the references are older. 

Kind regards

Round 2

Reviewer 1 Report

I accept current version of the text.

Reviewer 3 Report

I have no further comments.