Underwater Noise Characteristics of the Tidal Inlet of Zhanjiang Bay

Round 1

Reviewer 1 Report

This is a very limited data set from which the authors try to draw some significant conclusions. It is not clear to me what is new in this study, except for the fact that very few data are available from this region. Defining soundscapes and the components that make up these soundscapes is very complicated and difficult, as the authors point out. A number of studies have shown that the soundscape varies significantly both in time and space. I therefore do not think that these short snapshots are sufficient to define the soundscape and its sources. It also surprises me that the authors measure significant noise levels at the lowest frequencies in such a shallow water. Theory suggests that these low frequencies should not be able to propagate into waters with depths < 25 m. Also, the result that a significant portion of the measured noise spectra is wind generated puzzles me when the authors state that the wind speed during the measurement periods were less than 3 m/s? Finally, it is not clear to me what the novelty of this study is in terms of determining sources of noise when the results seem to follow closely the results and conclusions by Wenz back in the 1960s? I think the authors need to explain this better. Also, I wonder about the comparisons between the two time periods and the conclusion that one period was significantly noisier than the other. The fact is that the first observations were made at a depth of 10 m, while the second set of observations were made at 5 and 20 m. Could this difference explain the different results?

A few detailed comments:

The data presented in Figure 2 are very confusing to me. Are all the data shown in these figures, but the hydrophone was in air during the period with the white arrows? What does the sentence: ...(white arrows represent data from the water outlet of the hydrophone) mean? If my interpretation is correct, I find it very hard to see the actual good data in these figures. What does 'Measurement number' and 'Collection number' mean?

On line 191 the authors say that there is a clear correlation between the average sound pressure level and the tide level. I cannot see this in Figure 2. Perhaps add the tidal height to the panels in Figure 2 for clarity? Is this correlation caused by flow noise as a result of tidal flow, or is it as a result of water depth changes and therefore influences on wave guide propagation? 

Figure 8 caption needs to be updated to identify the green curves representing the present data set. It took me a long time to figure this out.

Figure 1b is misleading. It suggests that you had 3 hydrophones in the water, while it looks like you had one in September and 2 in March?

Table 1 caption does not make sense. I don't think there is any statistical information in this table? Perhaps also add the actual recording duration with each time in the table to indicate how much data was used in the study. What was the sampling rate of the hydrophone system?

The grammar is pretty good. However, there is a lot of sloppiness and jargon in describing methods and results. The figure and table captions are not detailed enough to describe what is being shown. Figure labels are very small and hard to read.

Author Response

see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

 

The paper entitled “Underwater Noise Characteristics of the Tidel Inlet of Zhanjiang Bay” aims at characterize the Noise activity on the tidal Inlet of the Zhanjiang Bay. The work presents several criticalities which make it confusing and incomplete. Nevertheless, the research topic is interesting (even if not completely new: some works already existing in Literature) and the experimental setup seems to have potentialities. For this reason I suggest to publish the paper, but only  after positive reply to the following major concerns, and relative implementation on the Manuscript.

 

1)     One of the main concern regards the introduction section, which is missing of the main topic of the work: the tidal activity. Why it is important in relation to underwater noise activity? Why it has to be studied? Note that the word “tide” is mentioned for the first time in the last sentence of the Introduction, which is not acceptable since the title of the Manuscript clearly report the aim of investigate noise in relation to the tidal activity. Moreover, there is no correlation between the Abstract (which is full of reference to the tidal activity) and the Introduction, where they are completely missing. I think an extensive rewriting of the section is mandatory.

 

2)     Sentence of lines 64 to 66 is quite confusing, and the order of the references is inverted ([20-23] before [17-19]). Please rephrase to make it clear.

 

3)     Data collection needs to be specified better:

 

a.      Was the hydrophone calibrated before and after the measurements?

b.      Why there is a difference between the depths of first measurement (Sept 12 2022, 10 meters) and the second one (March, 21, 2023)? In general, the experimental setup and environment needs to be clearer and more precise.

c.      Lines 118 and 125: “In the equation,…” is not clear, since there is more than one formula through the text. Please specify which equations the Authors are referring to.

 

4)     Line 130: why do the Authors define the underwater area of experiment as “ocean”? Isn’t the area of the experiments a bay? It’s not clear.

5)    Results of Figure 2 need a deeper understanding,  so the Authors should be more precise in the explanation. How can it be assessed that “sound pressure levels in the second experiment were significantly higher” (line 137) if there is no numerical  value nor statistical analysis? It is important to statistically evaluate the data, which cannot be simply inferred by a graph.

6)     Same for figure 3 and the connected description of results (lines156 to 158): without a statistical description of data, even if basic, conclusions cannot be trusted.

7)     Lines 177 to 187: the authors should kindly provide a description of the methodology by the tidal levels were measured.

8)     Lines 206-208  and 210-212 are repeated.

9)     Results shown in Figure 7 are not clear: the Authors should please extensively define the correlation matrix meaning, if the frequencies belong to the same measurements or different ones. In general, since it seems to be the primary outcomes of the work, the Discussion section related to Figure 7 needs to be described way more accurately.

 

 

Moderate English check has to be performed.

Author Response

see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The Authors carefully replied to the rewiever's comments, and substantially modified the original Manuscript improving its readibility and its scientific soundness. In the reviewer's opinion the Manuscript can be published. Nevertheless, a short list of some suggestions is included, which could furtherly improve the work:

1. Some minor English editing could help in removing some typos, rephrase some sentences and  avoid repetitions.

2. Figure 6 and figure 7 are not clearly visible due to the similarity of lines color (expecially a and c). Suggestion is to change colors.

3. In table 2 bold text could be removed 

Some minor editing could help in furtherly improving the Manuscript.