the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Dec 2024
Is It Feasible to Use a Single Remote Sensing Optical Water Index for Rapid Mapping of Water Resources?
Abstract. Water resources are an important component of the earth's system, and the frequent occurrence of floods and droughts in the context of current climate change makes rapid and accurate monitoring of water resources particularly important. The optical water index (OWI) is a commonly used method for extracting water areas on the basis of remote sensing images, often with a high level of automation. However, selecting the right OWI is challenging due to the variety of water types. To quantitatively evaluate the differences in the mapping potential of different OWIs for surface water, we selected 12 commonly used OWIs to conduct comparative experiments among five types of surface water based on Landsat-8 and Sentinel-2 images. The results revealed that the Normalized Difference Water Index (NDWI) was better for turbid water, the Multi-Band Water Index (MBWI) was better for shaded water, the Modified Normalized Difference Water Index (MNDWI) was better for green water, and the Automated Water Extraction Index (AWEIsh)was better for swamp water and saltwater. Sentinel-2 has a higher ability to classify water than Landsat-8. Our work provides prior experience for fast and accurate water resources mapping in case of floods or droughts.
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RC1: 'Comment on nhess-2024-214', Anonymous Referee #1, 05 Feb 2025
The manuscript by Wang et al. uses Sentinel-2 and Landsat-8 imagery to evaluate the performance of 12 water mask indexes for masking water pixels in flooded areas, considering five water types as test cases. The study concludes that different water mask indexes are optimal for each of these five water types, thus water type must be considered when choosing the water mask to be used for mapping flooded areas.
The manuscript provides useful tools to aid the choice of the best water mask for different regions, water types, and case studies. Figures and tables are very informative. However, the text and the manuscript structure require drastic changes. For example, lines 53 to 92, where the water mask indexes are explained, should be in the Methods, not in the Introduction. There is a section “Method” within the section “Material and Methods”. There is no section to provide details on the satellite data that were used, there is only one sentence about it in the “Data” section. Lines 252-257 should be in the Discussion section.
Moreover, English language and grammar require critical revision. There are many grammar errors in the text, including verb conjugations, sentences that are too long or built incorrectly, and misspelled words. In addition, there are portions of the text such as lines 98-101, where one sentence is repeated twice, which indicates that the manuscript was not carefully revised by the authors. The poor language makes it often difficult to understand what the authors mean with some statements.
For these reasons, I believe the manuscript should be rejected, to allow significant improvement before resubmission.
In addition to the problems pointed out above, the following points are important:
- The water types are classified as turbid, green, shaded, swamp, and salt waters. However, the criteria for defining these water types are not described.
- There is no definition for the term “surface water”, often mentioned in the manuscript.
- There are no details about the in-loco observations (field surveys) mentioned in line 104. Conversely, according to Fig. 3, model accuracy was tested by comparing outputs of the different models to the output of SWI. If that’s the case, what are the field surveys for? Please explain and organize this explanation in the text.
- Equations for 11 water masks, not 12, are shown in Table 1.
- Thresholds for water classification, for each index, are not provided. The method used to select this threshold is also not provided.
Minor suggestions:
- Paragraph of line 90 should be in the legend of Table 1, since it describes the table content, and the table legend itself is incomplete.
- Line 116-117: in “At present, the water bloom in Taihu Lake is still serious.”, please explain what a “serious bloom” is.
- Legends of all figures and tables are too short and do not explain what the content is.
- Section 4.1: What phenomenon?
Citation: https://doi.org/10.5194/nhess-2024-214-RC1 -
AC1: 'Reply on RC1', Yuqing Wang, 11 Feb 2025
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-214/nhess-2024-214-AC1-supplement.pdf
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CC1: 'Comment on nhess-2024-214', Chenxi Shi, 06 Feb 2025
This article entitled “Is It Feasible to Use a Single Remote Sensing Optical Water Index for Rapid Mapping of Water Resources?” examines the applicability of an optical water index with prospective implications for rapid mapping of water resources during disasters. I think this is a very interesting work, and the quality of the manuscript is generally excellent and up to the standard of manuscripts in the journal Natural Hazards and Earth System Sciences. However, I suggest some revisions before publication, as indicated by the following.
- P2, L32: The combination of OWIs and SAR for flood mapping is indeed common, but what is the difference between the two and what are the advantages of OWIs?
- P3, L83, 84: This paragraph could be merged with the previous one.
- P8, Fig. 2(b) Swamp and Vegetation colors are not easily distinguishable and need to be modified.
- P9, once again, Fig3 has some colors very close together, make changes.
- The Discussion includes “Explanation of the phenomenon”and “Drawbacks”; the author should add a related parties with future research.
- The Conclusionsare short and could usefully be augmented to emphasize the significance of the work.
Citation: https://doi.org/10.5194/nhess-2024-214-CC1 -
AC2: 'Reply on CC1', Yuqing Wang, 11 Feb 2025
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-214/nhess-2024-214-AC2-supplement.pdf
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RC2: 'Comment on nhess-2024-214', Lino Augusto Sander de Carvalho, 21 Feb 2025
The manuscript utilizes satellite imagery (Landsat-8, Sentinel-2) to assess the quality and performance of water mask indices. A total of 12 indices were tested, considering five “global” water types as case studies. The results of this work are valuable and relevant for remote sensing applications on a global scale, and the manuscript could be considered for publication after addressing a series of suggestions and corrections.
In my opinion, the primary concern lies in the structure of the manuscript. Several issues throughout the text, which are highlighted in the attached PDF, hinder the clarity and understanding of key points, particularly in the methodology and results sections. For these reasons, I recommend rejecting the manuscript at this stage, to allow the authors to make substantial improvements before resubmission.
I encourage the authors to review the attached PDF and am available to clarify any questions that may arise during the revision process.
Best
Lino Sander
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AC3: 'Reply on RC2', Yuqing Wang, 24 Feb 2025
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-214/nhess-2024-214-AC3-supplement.pdf
-
AC3: 'Reply on RC2', Yuqing Wang, 24 Feb 2025
Status: closed
-
RC1: 'Comment on nhess-2024-214', Anonymous Referee #1, 05 Feb 2025
The manuscript by Wang et al. uses Sentinel-2 and Landsat-8 imagery to evaluate the performance of 12 water mask indexes for masking water pixels in flooded areas, considering five water types as test cases. The study concludes that different water mask indexes are optimal for each of these five water types, thus water type must be considered when choosing the water mask to be used for mapping flooded areas.
The manuscript provides useful tools to aid the choice of the best water mask for different regions, water types, and case studies. Figures and tables are very informative. However, the text and the manuscript structure require drastic changes. For example, lines 53 to 92, where the water mask indexes are explained, should be in the Methods, not in the Introduction. There is a section “Method” within the section “Material and Methods”. There is no section to provide details on the satellite data that were used, there is only one sentence about it in the “Data” section. Lines 252-257 should be in the Discussion section.
Moreover, English language and grammar require critical revision. There are many grammar errors in the text, including verb conjugations, sentences that are too long or built incorrectly, and misspelled words. In addition, there are portions of the text such as lines 98-101, where one sentence is repeated twice, which indicates that the manuscript was not carefully revised by the authors. The poor language makes it often difficult to understand what the authors mean with some statements.
For these reasons, I believe the manuscript should be rejected, to allow significant improvement before resubmission.
In addition to the problems pointed out above, the following points are important:
- The water types are classified as turbid, green, shaded, swamp, and salt waters. However, the criteria for defining these water types are not described.
- There is no definition for the term “surface water”, often mentioned in the manuscript.
- There are no details about the in-loco observations (field surveys) mentioned in line 104. Conversely, according to Fig. 3, model accuracy was tested by comparing outputs of the different models to the output of SWI. If that’s the case, what are the field surveys for? Please explain and organize this explanation in the text.
- Equations for 11 water masks, not 12, are shown in Table 1.
- Thresholds for water classification, for each index, are not provided. The method used to select this threshold is also not provided.
Minor suggestions:
- Paragraph of line 90 should be in the legend of Table 1, since it describes the table content, and the table legend itself is incomplete.
- Line 116-117: in “At present, the water bloom in Taihu Lake is still serious.”, please explain what a “serious bloom” is.
- Legends of all figures and tables are too short and do not explain what the content is.
- Section 4.1: What phenomenon?
Citation: https://doi.org/10.5194/nhess-2024-214-RC1 -
AC1: 'Reply on RC1', Yuqing Wang, 11 Feb 2025
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-214/nhess-2024-214-AC1-supplement.pdf
-
CC1: 'Comment on nhess-2024-214', Chenxi Shi, 06 Feb 2025
This article entitled “Is It Feasible to Use a Single Remote Sensing Optical Water Index for Rapid Mapping of Water Resources?” examines the applicability of an optical water index with prospective implications for rapid mapping of water resources during disasters. I think this is a very interesting work, and the quality of the manuscript is generally excellent and up to the standard of manuscripts in the journal Natural Hazards and Earth System Sciences. However, I suggest some revisions before publication, as indicated by the following.
- P2, L32: The combination of OWIs and SAR for flood mapping is indeed common, but what is the difference between the two and what are the advantages of OWIs?
- P3, L83, 84: This paragraph could be merged with the previous one.
- P8, Fig. 2(b) Swamp and Vegetation colors are not easily distinguishable and need to be modified.
- P9, once again, Fig3 has some colors very close together, make changes.
- The Discussion includes “Explanation of the phenomenon”and “Drawbacks”; the author should add a related parties with future research.
- The Conclusionsare short and could usefully be augmented to emphasize the significance of the work.
Citation: https://doi.org/10.5194/nhess-2024-214-CC1 -
AC2: 'Reply on CC1', Yuqing Wang, 11 Feb 2025
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-214/nhess-2024-214-AC2-supplement.pdf
-
RC2: 'Comment on nhess-2024-214', Lino Augusto Sander de Carvalho, 21 Feb 2025
The manuscript utilizes satellite imagery (Landsat-8, Sentinel-2) to assess the quality and performance of water mask indices. A total of 12 indices were tested, considering five “global” water types as case studies. The results of this work are valuable and relevant for remote sensing applications on a global scale, and the manuscript could be considered for publication after addressing a series of suggestions and corrections.
In my opinion, the primary concern lies in the structure of the manuscript. Several issues throughout the text, which are highlighted in the attached PDF, hinder the clarity and understanding of key points, particularly in the methodology and results sections. For these reasons, I recommend rejecting the manuscript at this stage, to allow the authors to make substantial improvements before resubmission.
I encourage the authors to review the attached PDF and am available to clarify any questions that may arise during the revision process.
Best
Lino Sander
-
AC3: 'Reply on RC2', Yuqing Wang, 24 Feb 2025
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-214/nhess-2024-214-AC3-supplement.pdf
-
AC3: 'Reply on RC2', Yuqing Wang, 24 Feb 2025
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