Evaluation and Improvement of No-Ground-Truth Dual Band Algorithm for Shallow Water Depth Retrieval: A Case Study of a Coastal Island

Round 1

Reviewer 1 Report

1.        In Equation (5), Equation (7a) and Equation (8c), ρ represents the water bottom reflectivity, how to get it? What’s the relationship between ρ and different substrate types?

2.        How do you determine "pairs of points with the same water depth and different substrates" in 4.3?

3.        Chen et al. (2019) proposed a dual band algorithm for shallow water depth retrieval with no ground truth. As It is mentioned in the title “improvement of no-ground-truth dual band algorithm”, could the authors explain the differences your research is from theirs. Though the paper is listed in the reference list, I miss a clear comparison with that method. I think such a comparison is essential to assess the significance of the scientific contribution.

4.        Figure 1, the scale bar and north arrow should be added. The longitude value of Wuzhizhou Island is incomplete.

5.        Note the placement of heading of 2 in manuscript.

6.        I would recommend a little more clarity in the description of the data, such as acquisition time and depth accuracy of the airborne LiDAR data. WV3 also provides 8-band multispectral images, so the word “unique” isn’t proper here.

7.        Figure 2, you mentioned that the maximum depth is 17.25 m, why is it marked 19 m? What is the reason for classifying the depth range into such kind of classes?

8.        Pay attention to specific words in your manuscript, for example, "pretreatment" (heading of 3) and "pre-processing"(Figure 3), “absolutefactor” and “abscalfactor"(see in the metadata file).

9.        There are mistakes in Equation (2), and the meanings of different parameters in Equation (2) and Equation (3) should be explained separately. I suggest adding the references of these methods.

10.     The signs(m0 and m1) after the Equation(20) are not uniform.

11.     There is a discrepancy between the description (the paragraph before Figure 3) and the Figure 3. Maybe it is proper to change the word “steps” to “parameters”.

12.     The paragraph after Figure 3, IOP is short for “intrinsic optical proposed”, not “inherent optical property”?

13.     The paragraph after Figure 4, “the Goodman method can rectify the obvious error better than the Hedley method, and thus cause different optical deep-water range in the study.” Since the Goodman method is better, why did you choose Hedley?

14.     The second paragraph in 3.2.4 is irrelevant to tide correction and should be moved to Data part.

15.     Equation (12a) and Equation (12b) are inconsistent with Equation (20a) and Equation (21a) in Chen et al. (2019).

16.     6.1, nearly 1000 points were used for regression, how many points for validation?

17.     6.2, what are the features of seagrass on the images? How to distinguish seagrass from coral and sand from coral sand? What does Table 8 indicate since the index range of same substrates varies so dramatically in different times?

18.     "Adjacent pixels" mean two adjacent pixels on the image? But in Figure 11, some pairs of points do not seem to be right next to each other. The pairs of points are selected with the same substrate types of different depths, not with different substrate types of the same depth?

19.     The figures should be numbered in the order of the appearance in the text. Figure 8 appears earlier than Figure 6 and Figure 7.

20.     There are errors in the statement and figures that need to be corrected, for example, two Figure (7d), same date in Table 5, “upward radiation and upward radiation”, no horizontal axis title in Figure 9 and Figure 12(d), etc.

21.     Some sentences are hard to understand, such as the the last sentence of the first paragraph in 3.2.4. The manuscript needs further polishing.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

A new dual band model is used for the shallow water depth in the study. Wuzhizhou Island is selected for the application. The subject is important and the study is valuable in terms of shallow water depth. Some suggestions and comments to the authors are presented below:

1. There are missing parts in the flowchart, Figure 3. What is the next step after “Accuracy of the results”? The flowchart should be revised carefully.

2. What are the units of the variables under “Methodology”?

3. Nearly 1000 data points are used for the linear bathymetry regression model. How did the authors decide or select these points, randomly or is there any algorithm for this procedure?

4. Conclusions part can be improved in the paper. Here is presented in a general concept. Main conclusions of the study should be explained well.

5. What is the novelty of the paper? The used algorithms are mentioned in the paper. Supported and related studies should be strongly presented in the paper by emphasizing the novelty of the paper.

3. The performance metrics part is very important for the evaluation of application results. For this aim, more performance metrics as NSE, Volume Error (VE), R-squared, etc. from literature should be calculated. Then, they can be given in a table. Because of the importance of the assessment of results, these metrics are widely used in the literature, especially in the extreme event studies.

4. Literature part is looking weak. Give new and last updated examples from literature about “shallow water” as “doi.org/10.18400/tekderg.416067”, “doi.org/10.1007/s12237-022-01053-1”

5. The flowchart of the bathymetric model in Figure 5 can be simplified for the readers. There are some missing parts about model. How can you decide for the initial and boundary conditions of the parameters of the model?

 

6. The statistical properties as skewness, coefficient of variation, confidence intervals and distribution characteristics, etc. of used data as mean, min, max and median of used data as shallow water should be given in a table.

Author Response

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Reviewer 3 Report

The authors have satisfactorily and concisely presented their work, but the figures and tables, although they are correct, are not presented according to the template prescribed by the Remote Sensing magazine. It would be good to show a scale in Figure 1, and the figure of Wuzhizhou Island should be shown enlarged and necessarily with a scale. Figure 2 is "clumsy" and the scale, legend and out-of-frame content should be fixed. The same comments apply to figure 8, 10, 11 and 13 as for figure 2.

Author Response

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Round 2

Reviewer 1 Report

The authors revised the manuscript carefully, and made a relatively detailed reply. I think the submission has been greatly improved and is worthy of publication.

Reviewer 2 Report

I suggest accepting the manuscript.