Evaluating the German Ground Motion Service for Operational Dam Monitoring: A Comparison of InSAR Data with In Situ Measurements

Round 1

Reviewer 1 Report

This study evaluates the applicability of Sentinel-1 Persistent Scatterer Interferometry (PSI) data from the Ground Motion Service Germany (BBD) for monitoring dams by comparing it with terrestrial measurements at dams of the Ruhrverband in North Rhine-Westphalia (NRW), Germany. This paper is more like an evaluation report than a research paper, and it is recommended that the author make major revisions to the content and structure of the document.

The minor modifications are as follows:

1. The numbering of the figures in the article is incorrect, and the entire text needs to be revised.
2. In Figure3, Why are the vertical and east-west points in the water?
3. Suggest redrawing Figures 4, 5, and 6 as the color differentiation of the curves is relatively small.

Author Response

Comments 1: This study evaluates the applicability of Sentinel-1 Persistent Scatterer Interferometry (PSI) data from the Ground Motion Service Germany (BBD) for monitoring dams by comparing it with terrestrial measurements at dams of the Ruhrverband in North Rhine-Westphalia (NRW), Germany. This paper is more like an evaluation report than a research paper, and it is recommended that the author make major revisions to the content and structure of the document.

Respone 1: Thank you for the comment. The manuscript has been revised to clarify how “operational” is addressed. The study is framed as an observational multi-site assessment with predefined, DIN-aligned evaluation criteria (e.g., observables, update frequency, accuracy/interpretability, documentation). The statistical evaluation (r, RMSE, MAE/MedAE, significance) and the versioned comparison (2015–2020 vs. 2015–2021) go beyond a descriptive service review. We also use the term “operational support” where appropriate and specify where criteria are met or not (e.g., vertical component, update latency). These changes maintain the manuscript’s structure while clarifying its research design, testable criteria, and generalizability. The changes can be found in the revised introduction on page 2/3 and throughout the whole manuscript (pages 5, 7, 8, 10. Changes are all marked in red)

Comment 2: The numbering of the figures in the article is incorrect, and the entire text needs to be revised.

Answer 2: Thank you for this comment. We have corrected all the numbers below the figures and in the text. These changes can be found below every figure and table that needed to be corrected.

Comment 3: In Figure3, why are the vertical and east-west points in the water?

Answer 3: We thank the reviewer for the comment. The vertical and east–west data derive from the 50 m gridded BBD decomposition. Values are aggregated per grid cell from LOS PS time series, and the map shows the grid cell centroids rather than physical PS locations. As a result, some markers plot over water although the contributing scatterers are on nearby structures within the same cell. We have clarified this in the Methods (page 5) and in the Figure 3 caption.

Comment 4: Suggest redrawing Figures 4, 5, and 6 as the color differentiation of the curves is relatively small.

Answer 4: We have slightly increased the size of the figures in the manuscript to make it easier to distinguish the lines. However, we would like to maintain a neutral color scheme, which is why we decided not to completely revise the figures. These changes can be found in Figures 4, 5, and 6.

Reviewer 2 Report

Dear authors,

first I recommend you to better introduce the topic and to cite clearly (not just via 'reference numbers' , eg. 9-13) comparable studies on dams .. presenting also one interesting example elsewhere in the world - otherwise the study looks too 'regional'.

Then, please, add a scale in two of the first figures.

In the discussion/conclusions .. please come back to some comparisons with other studies introduced in the beginning.

yours

reviewer H

Some general English review recommended .. for instance what do you mean by:

'How the quality of these points will behave remains a subject for future statistical and visual analyses ...' ?

Author Response

Comment 1: first I recommend you to better introduce the topic

Answer 1: We have thoroughly revised the introduction and framed the topic more clearly. Thank you for the suggestion. The whole introduction has been changed/reworked. These changes can be found on pages 2 and 3.

Comment 2:  …and to cite clearly (not just via 'reference numbers' , eg. 9-13) comparable studies on dams .. presenting also one interesting example elsewhere in the world - otherwise the study looks too 'regional'.

Answer 2: Our use of numerical citations follows the MDPI style guidelines. We chose to use reference numbers consistently throughout the manuscript to maintain a uniform system and to avoid unnecessarily lengthening the text by adding author names in the prose. We have integrated comparable studies in the state-of-the-art section; however, the present study, in this specific form, has not been conducted before. It is deliberately focused on our project partner, the Ruhrverband in western Germany, in order to evaluate the usability of GMS data against high-resolution in-situ measurements. However, in the newly revised introduction, several international examples were added to highlight the relevance of PSI and dam monitoring. This can also be found in the new introduction pages 2 and 3.

Comment 3: Then, please, add a scale in two of the first figures.

Answer 3: Thank you for the note. Although these are general overview maps, we have added a scale. This change can be found on page 4, figure 1.

Comment 4: In the discussion/conclusions .. please come back to some comparisons with other studies introduced in the beginning.

Answer 4: That’s a good point. We believe it rounds off the study nicely. We have incorporated this, thank you. These changes can be found on page 20, 21, and 22, changes ar marked.

Reviewer 3 Report

The authors claim to evaluate the Ground Motion Service Germany for Operational Dam Monitoring. It is not very clear how the operational monitoring is addressed. To my opinion, this evaluation should address the standards required to the existing operational monitoring techniques. And, based on these standards, clearly state the key performance parameters that are required to consider operational the monitoring based on interferometric SAR results. And then, evaluating the comparison results. 

The authors are invited to address these aspects.

I would remove statistical from the title.

In Table 5 add the units for RMSE.

Author Response

Comments 1: The authors claim to evaluate the Ground Motion Service Germany for Operational Dam Monitoring. It is not very clear how the operational monitoring is addressed. To my opinion, this evaluation should address the standards required to the existing operational monitoring techniques. And, based on these standards, clearly state the key performance parameters that are required to consider operational the monitoring based on interferometric SAR results. And then, evaluating the comparison results. 

Answer 1: The term “operational” has been clarified as “operational support” throughout the manuscript. A concise set of criteria (derived from German dam-monitoring practice and relevant DIN standards (DIN 19700 series; DIN 18710)) now frames the evaluation. The Discussion and Conclusions explicitly state where these criteria are met and where limitations remain (e.g., vertical component, update latency). The study is thus positioned as a step towards operational support, not as a full operational qualification. This changes can be found in the reworked introduction on pages 2 and 3, and throughout the manuscript at various spots (pages 8, 10, 24).

Comments 2: I would remove statistical from the title.

Answer 2: We have removed the word from the title. This change can be found in the title.

Comments 3: In Table 5 add the units for RMSE.

Answer 3: The units have been added, thank you for the note. This changes can be found in Table 6 (was Table 5 before).