Detection and Evaluation of Flood Inundation Using CYGNSS Data during Extreme Precipitation in 2022 in Guangdong Province, China
Round 1
Reviewer 1 Report
Dear Authors,
The present manuscript the Cyclone Global Navigation Satellite System (CYGNSS) L1 Science Data were processed to obtain the change of Delay-Doppler Map (DDM) and Surface Reflectivity (SR) during the flood event. In order to study the impact of extreme precipitation in Guangdong Province in 2022. The paper presents interesting results for future analyses, which may serve as a basis for future applications in different locations. In my opinion, this manuscript requires major revision, and the following issues should be considered/clarified prior to acceptance. I suggest a major revision.
1. The abstract needs to clarify the purpose of this article.
2. The introduction needs more details of the methodology used. If it was applied in other studies, or compared with the state of the art.
3. The introduction also needs to clarify the importance of this study, justifying the reason for this research
4. There is no connection between the paragraphs in introduction.
5. Highlight more clearly the justification of the study.
6. The objectives are not well described. What are the secondary objectives?
Results and Discussion
7. In general, the results are well presented and demonstrate the importance of the study. However, a better discussion with the factors that contribute to the isotopic signals is lacking. And the effects that can occur to lead to these results.
Conclusion
8. The conclusion repeats a lot of what was presented in the results. And it does not answer all the proposed objectives. It needs to be improved.
Author Response
Dear Editor and reviewers:
We really appreciate your valuable comments and suggestions. We have carefully addressed the reviewers’ comments and suggestions. Many parts have been rewritten. Any revisions in the manuscript have been marked up in red font. We hereby provide our point-by-point responses to each of the reviewer’s comments.
Please kindly see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Your flood inundation detection approach using CYGNSS is an important investigation to provide better accuracy for flood inundation estimation and analysis. Consequently, I would like to congratulate you on your topic.
Your introduction provides sufficient and relevant background and appropriate references. I feel that you could discuss 3-dimensional approaches as well, as these are discussed in the industry. I understand that you may be following a separate path, but it is always nice to improve your discussion with 2D and 3D flood simulation/estimation models. An introduction to approaches were provided in Teng, and others are simply some 3D approaches:
Teng, J. et al. Flood inundation modelling: A review of methods, recent advances, and uncertainty analysis.
Hadimlioglu I. A. et al. FloodSim: Flood Simulation and Visualization Framework Using Position-Based Fluids
Van Ackere, S. et al. Development of a 3D dynamic flood WebGIS visualization tool.
Beyond your introduction, your study area is well defined, and it is an interesting region of China, especially for flood analysis.
168, you indicate: "Although a large number of observation data are discarded after data processing, CYGNSS can 169 still provide enough data for soil moisture inversion."
>I am assuming that these are discarded due to low quality in data. If there are some specific reasons, please indicate and clarify.
227 "it can be clearly display the difference between distributions of CYGNSS SR before and after flood." I believe you want to say "it can clearly display..."
239 > So random forest is advantageous due to overcoming overfitting problems? Is there any specific reason for random forest classification here?
Figure 5 looks good to visualize precipitation changes. Nice.
284 > You indicated that the surface reflectance values are selected as -14dB and -17dB. These values are derived from experiments, or are they the best values for the purpose of your study? You could explain.
Figure 7, again a nice visualization here.
In your discussion and conclusion portion, it is noted that this approach is feasible for tracking flood inundation. That's all right. However, it does not specifically underline that this approach is suitable for real-time tracking. Is it? Can you please clarify that in conclusion, either as a success, or as a limitation, that full real-time may not be possible.
Also, this is just a question, do you think urban areas with added buildings, road networks, etc., would affect your surface condition parameters? Would you be able to use this approach for urban areas? Is it only suitable for rural areas? If there are significant differences, you could briefly indicate so.
Thanks!
Author Response
Dear Editor and reviewers:
We really appreciate your valuable comments and suggestions. We have carefully addressed the reviewers’ comments and suggestions. Many parts have been rewritten. Any revisions in the manuscript have been marked up in red font. We hereby provide our point-by-point responses to each of the reviewer’s comments.
Please kindly see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This is a study with practical significance, focusing on the impact of extreme precipitation on flood in Guangdong Province in 2022. Based on the bistatic radar equation, CYGNSS data is used to display the inundated areas in Guangdong Province in different periods, and the results are compared with SMAP soil moisture data and precipitation data. DWAAI is introduced to identify flood occurrence. The research results provide a feasible scheme for flood disaster research. This study is novel and worth publishing.
However, there are some problems that I suggest the author solve before publishing.
1. English language and style: Moderate English changes required.
2. When using the bistatic radar equation to solve the surface reflectivity of CYGNSS, does the author need to consider the impact of the receiver incidence angle on the surface reflectivity?
3. The longitude and latitude format in Figure 2 is different from that in Figure 3 and Figure 5, and they should be unified.
4. The Tanjiang River Basin is shown in the blue box in Figure 6, but it is interpreted as the forest covered area in the southwest in the paper, which should be corrected.
5. The SMAP data loss area in Figure 13 should be marked with a red box.
6. In Section 3.6, DWAAI, SMAP soil moisture and precipitation are used for comparative verification with CYGNSS surface reflectance. The author should consider calculating their correlation and making some text modifications.
Author Response
Dear Editor and reviewers:
We really appreciate your valuable comments and suggestions. We have carefully addressed the reviewers’ comments and suggestions. Many parts have been rewritten. Any revisions in the manuscript have been marked up in red font. We hereby provide our point-by-point responses to each of the reviewer’s comments.
Please kindly see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Based on the CYGNSS L1 V3.0 data, the author shows the drawing of the submerged area map of Guangdong Province, and uses SMAP observations and precipitation data for verification. Overall, the topic is interesting and a hot topic of current research, but needs further refinement before publication.
1. The introduction should clearly indicate the novelty of this research, is it data innovation? Or method innovation?
2. Besides, the introduction part spends a lot of space explaining the applicability of CYGNSS data in flood detection. It is suggested that some domestic and foreign research progress in flood detection should be appropriately added to further highlight the innovation and research significance of this study.
A Novel Dual-Branch Neural Network Model for Flood Monitoring in South Asia Based on CYGNSS Dataï¼›
A New Coherence Detection Method for Mapping Inland Water Bodies Using CYGNSS Dataï¼›
INTRODUCING THE GLOBAL MAPPING OF FLOOD DYNAMICS USING GNSS-REFLECTOMETRY AND THE CYGNSS MISSIONï¼›
Nonstationarity-based evaluation of flood frequency and flood risk in the Huai River basin, China. Journal of Hydrology.
3. It is suggested to increase the location of the study area in China in Figure 1, and it is not enough to show only Guangdong Province.
4. In sections 2.2-2.4, research data and research methods need to be separated.
5. A variety of data sources are used in the data source and processing, data preprocessing and other analysis, pure text expression is not very intuitive, it is recommended to make a research framework diagram, which is clear at a glance.
6. Line219-230 mentions the interpolation method for spatialization, and it is recommended to add specific methods and references, for example: Kriging interpolation. Such as
7. Can you give specific reasons or references for the threshold setting in section 3.1 to explain the rationality of the threshold setting.
8. In this paper, the detection of flood inundation is based on soil moisture. How to explain that the method based on soil moisture is better than the more direct method based on identifying changes in water bodies? Why not combine other methods, such as Sentinel-1, Landsat, etc. to identify and extract water body information, and compare them to show that the method for identifying water body submersion in this study is better?
9. The precipitation data used in the study is CLDAS-v2.0, whether it is reliable or not is worth pondering. It is recommended to add relevant references to confirm the reliability of this dataset.
Author Response
Dear Editor and reviewers:
We really appreciate your valuable comments and suggestions. We have carefully addressed the reviewers’ comments and suggestions. Many parts have been rewritten. Any revisions in the manuscript have been marked up in red font. We hereby provide our point-by-point responses to each of the reviewer’s comments.
Please kindly see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear Authors,
The authors performed an extensive correction of the previous version. Making the proposed corrections and/or suggestions. Therefore, I suggest the publication of the manuscript.
Author Response
Dear Editor and reviewer,
We really appreciate your valuable comments and suggestions. According to the editor's suggestion, we made substantial modification of the English language in the revised manuscript. Any revisions to the manuscript have been marked up using the “Track Changes” function. Details please see the attached file.
Author Response File: 
Author Response.docx
