Leveraging Ice, Cloud, and Land Elevation Satellite-2 Laser Altimetry and Surface Water Ocean Topography Radar Altimetry for Error Diagnosis in Hydraulic Models: A Case Study of the Chao Phraya River

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript utilized the latest ICESat-2 and SWOT satellites to observe water level changes in the Chao Phraya River. These data could improve the data availability and thus enhance the performance of hydraulic models. It’s well written and the results are clearly presented. The conclusions are convincing. I only have several minor comments.

 

Please clarify the date availability of the satellite observations and explain their improvement compared to in-situ observations. A map of improvement in data availability in percentage is recommended.

 

L66-L69, in the review of ICESat-2 applications, please explain the target and advances of the studies, rather than just a list of regions. The same goes to the review of SWOT.

 

Fig. 6a part of the legend seems to be redundant. The same goes to fig. 7a.

6b, the two colors are too close.

6d, improve the readability of the texts. The colors are not explained.

Fig. 8, Make the x- and y-axes the same scale.

D&E, it looks there are very limited number of observations in pairs. So it is hard to draw a conclusion. Is it possible to improve this by interpolation (maybe marked in a different color)?

L376, “not overlapping in time”, please add a plot to show the available dates of different products.

Fig. 10, change the unit of x-axis to km. Please correct this for all plots.

10a. please add a smoothed curve to the scatter points.

The difference between simulated and satellite-observed (by ICESat-2 and SWOT) reaches the largest value of -1.0 m at the chainage of about 240 km. However, the in-situ value indicates that the simulated value is quite accurate. How to explain this discrepancy?

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

This paper investigates the application of ICESat-2 laser altimetry and SWOT radar altimetry data for diagnosing errors in hydraulic models using the Chao Phraya River as a case study. The research has notable scientific and practical significance. The proposed workflow is logical and well-structured. The authors effectively integrated ICESat-2 and SWOT satellite data to validate the simulated water surface elevation (WSE) results. The model performance was evaluated using multi-dimensional approaches, including point comparisons, profile analysis, and spatial distribution maps. The analyses are clear, and the results are detailed, providing readers with a comprehensive understanding. However, several aspects require improvement.

First, the manuscript is overly lengthy and does not fully conform to the formatting requirements of Remote Sensing, which hampers readability. Second, the technical methods rely heavily on existing techniques, with limited innovative contributions. The authors are encouraged to explore methodological improvements or propose new analytical frameworks to enhance the academic impact of the study. Additionally, the paper lacks a thorough discussion of data limitations (e.g., spatial coverage and temporal resolution) and their potential influence on results. The conclusion section is somewhat vague, with insufficient focus on summarizing findings specific to the study area, results, and discussions.

Based on the above, I recommend a major revision to improve the manuscript's scientific value and readability. Below are specific suggestions for improvement:

 

1. Citation issues: Remove the regional specification “Tibetan Plateau” and incorporate the referenced study under “China.”
2. Figures: Certain figures (e.g., Figures 1, 2, 4, 6) are unclear when enlarged. Replace them with vector graphics and add coordinate axes, place names, hydrological station names, and track numbers to Figures 1 and 2.
3. Study area description: Include key information such as basin area, river gradient, precipitation, and evaporation to enhance the introduction of the study area.
4. Hydraulic model clarity: Provide a clearer description of the hydraulic model in Section 4.1.
5. Terminology consistency: Ensure consistent use of acronyms like WSE, CPY, SWOT, and ICESat-2 throughout the manuscript.
6. Data threshold explanation: Clarify the rationale for the 15-meter exclusion threshold mentioned in Line 288. Discuss whether this threshold risks excluding too much valid data.
7. Metric interpretation: Provide detailed explanations of the four accuracy metrics mentioned in Lines 322-325.
8. Data support insufficiency: The discussion in Section 6.2 on the influence of sea level on the CPY River is not well-supported by experimental data or results.
9. Accuracy verification: Include a validation of SWOT and ICESat-2 data accuracy in the study area, using hydrological station observations or established altimetry techniques for comparison.
10. Discussion focus adjustment: The extensive discussion on satellite data selection in Sections 7.1 and 7.2 should be streamlined. Instead, focus on factors like river width, slope, and environmental influences on altimetry accuracy and model errors.
11. Conclusion improvement: Revise the conclusion to provide more specific insights related to the study area, findings, and discussions.

Author Response

We have provided our response in the Word file. Please see the attachment.

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Reviewer 3 Report

Comments and Suggestions for Authors

This is a nice showcase demonstrating how ICESat-2 and SWOT WSE data are useful. I am confident that this manuscript would be accepted in the journal. Nevertheless, I find several problems in the manuscript, which should be revised. Therefore, I recommend a major review to reorganise the manuscript before acceptance.

First, I noticed that the authors did not fully consider temporal scales of WSE changes. Because the goal of this study seems to be the establishment of a flood warning system, I guess the simulation model includes various short-term variations, such as tidal intrusion from the Gulf of Thailand and barometric WSE changes, together with seasonal and interannual WSE variations. Unfortunately, however, I could not find descriptions of which phenomena are handled in the model. This issue is connected to another problem that I could not find “temporal matching criteria” in comparisons. At downstream stations such as CPY015, tidal signals are dominant (Fig. C2), so the comparisons would strongly depend on the observational temporal differences and tidal phases; meanwhile, temporal gap criteria can be more relaxed at upstream stations so that more data can be averaged to reduce noises. Therefore, it is important to clearly describe matching criteria.

 In addition, I also noticed that some descriptions (of models, ALT03, SWOT) are overlapped in several sections. For example, some descriptions, such as Figures 6B and 6C, can be moved to the appendix. Also, I could not follow why subsections 6.1-6.3 are separated from subsection 6.4.

Note that readers may find it difficult to follow the contents because the structure of the manuscript is not described in the introduction.

 

----------------Minor Comments

[Sections] Do not count “Abstract” as a section.

[p10, L210] Which version of SWOT L2_HR_RiverSP?

[P14, Subsection 5.4] They are too obvious.

[Figure 5] Clearly describe that the hydraulic model and in-situ data are independent; the in-situ data have not been used as input data in the model.

[Figure 6] Figures should be made in a self-explained manner; for example, “Distance” in panels B and C are “along satellite track across the CPY river”, while “Distance” in panel D is “along the CPY river”. Also, there are no explanations about colors of plots in panel D.

Author Response

We have provided our response in the Word file. Please see the attachment.

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Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The traditional radar altimetry technology is difficult in river monitoring, and the SWOT satellite technology provides a more reliable data source for inland water monitoring. I believe that this paper is an early academic paper that combines ICESAT-2 and SWOT for river hydraulic modeling, and it has a high value. In addition, the authors have carried out meticulous revision work in response to the first round of comments, and I recommend the acceptance of the paper.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

I have confirmed that the authors have revised the manuscript as I requested. I almost agree to accept this manuscript, but I need to suggest several minor points that should be revised.

[1] Figures are imcomplete. For example, the numbers in axes in Figs 1, 2, 4, etc. are not explained. They are not latitude and longitude.

[2] Treatment of C.2 station data in comparisons is unclear. As written in L165 and Fig. 5, C.2 station data are used as model boundary conditions. Therefore, they should be excluded in comparison with in-situ data (Table 3), but this exclusion is not clearly described.

In addition, L417 mentions that simulated results at C.2 are largely different from ALT03 and SWOT. Does this mean both SWOT and ALT03 are deviated from in-situ data that are used as the boundary condition of the model?

 

Author Response

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