Spatial Structure, Short-temporal Variability, and Dynamical Features of Small River Plumes as Observed by Aerial Drones: Case Study of the Kodor and Bzyp River Plumes
Round 1
Reviewer 1 Report
Reviewer comments
- General comments
This study uses drone aerial remote sensing technology, in-situ measurement, and satellite imagery to jointly monitor the spatial structure, temporal variability and dynamic characteristics of the Kodor and Bzyp river plumes, and reveals its physical formation mechanism. The effectiveness of river plume monitoring provides a new insight for monitoring the dynamic features of the small river plume.
Generally, the subject of this research is very interesting and the methods used are acceptable. I greatly appreciate the valuable field experiments. I think, however, the manuscript needs to be partially revised. After careful elaboration and clarification, this research may contribute to the existing knowledge system.
First of all, the introduction does not fully investigate the papers in the existing knowledge system. The author elaborates much previous works used airborne remote sensing to study sea surface processes including several studies focused on river plumes. The authors, have not entirely investigated all the previous studies on sea surface research. Therefore, in my view, the author needs to fully understand the application of satellite sensors in related research papers in this field. I will give a detailed explanation in the "specific comments" below, please refer to it carefully and modify it.
Second, the manuscript requires a lot of native English editing. There are plenty of errors in grammar, spelling, and sentence structure. I have provided some suggested changes in the "specific comments" below to improve this situation... but I skipped a lot!
Third, in the data and methods section, I highly recommend the authors to provide all the information to the reader before presenting any conclusion to the reader. The manuscript should also have a clearer connection with the field conditions, so more meteorological and climatological data are needed. Whether the shooting angle of the drone, the sun's altitude angle, and the weather conditions during the drone shooting will have a certain impact on the results, please carefully modify and elaborate.
As a result, I have some major reservations about the contribution of this work to the existing knowledge system, which prompted me to suggest a major revision of this manuscript.
- Specific comments
Throughout the manuscript:
All abbreviations in each part of the manuscript including abstract and contents, as well as in the Table and Figure, should be introduced for the first time despite how common or not the abbreviation is.
Title
I suggest that the author amend the title "Spatial structure, temporal variability, and dynamical features of small river plumes observed by aerial drones" to "Spatial structure, temporal variability, and dynamical features of small river plumes observed by aerial drones: a case study of Kodor and Bzyp river plumes".
Abstract
There is no need to go into details in an abstract. Please pay more attention to solve these and the main findings and conclusions obtained, so a modification is needed.
Keywords:
There are so many keywords that authors need further refinement, 3-5 keywords are the best. I suggest keeping them within 5 and try to choose keywords with the most prominent theme. The keywords "aerial drone" and "quadcopter" are repeated, please check and correct them carefully.
Introduction:
No scientific and reasonable hypotheses are made, making the text too descriptive. The hypothesis should be established and tested through observations, and the hypothesis should be demonstrated point-to-point around the research purpose, and finally, the problems solved and significance of the research should be summarized.
Line 56-57: I suggest that when describing the work of predecessors, the author discusses point-to-point who used what methods, what conclusions were drawn, what gaps and defects are still existing, and how this research should make up for it.
Line 48: It is recommended to modify "wind forcing" to "wind force";
Line 57: The research papers in this field have not been fully investigated, and the author should understand the application papers of spaceborne sensors in this field, such as medium-resolution remote sensing images (Landsat, Sentinel), high-resolution remote sensing images (Worldview, SPOT) applications in this field, please carefully modify and elaborate;
Line 65: It is recommended to modify "In this work we focus on" to "In this work, we focus on"; Line 75: suggest to change "The summary and the conclusions" to "The summary and conclusions";
Data and Methods
Line 80: suggest that "m3/s" be changed to "m3/s".
Line 86: suggest to change "the sea shore" to "the seashore";
Line 87-88："Concentrations of suspended sediments in the Kodor and Bzyp rivers are 300-500 and 100-300 g/m3 during high discharge periods" be changed to "Concentrations of suspended sediments in the Kodor and Bzyp rivers are 300-500 and 100-300 g/m3 respectively during high discharge periods".
Figure 1. Need to be renewed when drawing, it should indicate the area where the study area is located and the corresponding latitude and longitude information; I suggest adding units to the latitude and longitude of Figure 1, and adding a north arrow.
Line 110: It is recommended to modify "within the plumes and in the adjacent sea." to "within the plumes and the adjacent sea.";
Line 112: It is recommended to modify "using a ship board pump-through" to "using a shipboard pump-through";
Line 118: Pay attention to the use of the unit, which needs to be consistent with the context. It is recommended to modify "the height of 10 м at a pier on a distance of 30 m from the sea shore." to "the height of 10m at a pier on a distance of 30 m from the seashore."; "M" be changed to "m".
Line 129: It is recommended to change "Estimation of" is changed to "The estimation of";
Line 131: suggest to modify "pixel neighborhood for" to "pixel neighborhoods for";
Results
The author provides all information to the reader before providing any conclusions to the reader. The manuscript should also have a clearer connection with the field conditions, so more meteorological and climate data are needed to provide readers.
Line 145: suggest to modify "plumes was studied" to "plumes were studied";
Line 151-153: The manuscript only describes that turbidity of the Kodor River has a good correlation with the salinity, but does not mean that the salinity and turbidity of the Bzyp River also have a good consistency. Therefore, the statement "surface turbidity structure of the Kodor and Bzyp plumes observed by optical remote sensing is indicative of surface salinity structure of these plumes" is inappropriate, please check and modify it carefully.
Line 154: It is recommended to modify "Flooding discharge result in" to "Flooding discharge results in";
Line 155：suggest that "50 km2" be changed to "50 km2".
Line 160：Figure 2 suggests to modify "during draught period" to "during drought period"; "Figure 2.." be changed to "Figure 2.".
Line 165: suggest that "Figure 2" be changed to "Figure 3".
Line 176: It is recommended to modify "numerical modelling studies" to "numerical" modeling studies";
Figure 4. It is recommended to change "Red arrow" to "The red arrow";
Line 191: It is recommended to change "on 2 September 2018" to "on 2 September, 2018";
Line 219: It is recommended to change "the sea "floor" is changed to "the seafloor";
Line 227: It is recommended to change "Formation of this zone" to "The formation of this zone"; Line 228: It is recommended to change "sea floor" to "seafloor";
Line 229: It is recommended to change "Sea water" is changed to "seawater";
Figure 6 suggests to modify "White arrow" to "The white arrow";
Line 245-248: "Formation of this zone is caused by interaction of the inflowing river jet with sea floor at the shoal that induces deceleration of the jet and its increased mixing with saline and low-turbid sea water. Stable front bounding this low-turbid and high-saline zone inside the plume was observed on a distance of up to 1 km from the shoal" and Line 227-230 "Formation of this zone is caused by interaction of the inflowing river jet with sea floor at the shoal that induces deceleration of the jet and its increased mixing with saline and low-turbid sea water. Stable front bounding this low-turbid and high-saline zone inside the plume was observed on a distance of up to 1 km from the shoal" are repeated，please double check and rephrase carefully.
Line261-262: "Aerial observations performed at 16:16 did not show any surface manifestations of the eddy" and Line 257-258 "The beginning of formation of the eddy was registered at 14:42 (Figure 7b), then at 15:34 a well-developed eddy was observed (Figure 7c, 7d)" are contradictory, please double-check and correct.
Figure 8: Please explain that the satellite images used by Kodor plume and Bzyp plume are inconsistent.
Figure 9: Please explain why the aerial imagery used by Kodor plume and the satellite imagery used by Bzyp plume are not synchronized, and how the spatial resolution affects both observations.
Line 262: It is recommended to change "it dissipated during" to "it dissipated for";
Line 275: It is recommended to change " "but at its periphery" is changed to "but its periphery"; Figure 7. The notes of the chart generally do not cross lines, please pay attention to the layout of the document and modify it carefully;
Line 360: It is recommended that "were observed" is changed to "was observed";
Line 403: It is recommended to change "accumulates at" to "accumulate at";
Line 408: It is recommended to change "floating litter is mainly" to "floating litter are mainly";
Line 414: Suggestion change "foam and floating litter is" to "foam and floating litter are";
Figure 15. It is recommended to change "indicates stripe of" to "indicate stripe of";
Line 425-426：There are no numeric characters in Figure 14, so the statement "Numbers indicate time intervals in seconds from the beginning of observations" is redundant.
Line 428：I recommend starting the formula on a new line and editing it with the MathType formula editor.
Line 465: It is recommended to change "different time periods" to "different" periods";
Discussion
The discussion section is too descriptive, please pay more attention to revealing the formation mechanism of Kodor and Bzyp plumes, variability and dynamics.
Line 492: It is recommended to modify "despite the large number of deltaic rivers inflowing to World Ocean," to "despite a large number of deltaic rivers inflowing to the World Ocean,";
Line 498: It is recommended to modify "was payed" to " was paid";
Line 500: suggest changing "difference in" to "differences in";
Line 506: suggest changing "spreading over sea areas with" to "spreading over sea areas with"; Line 520: suggest changing "wind forcing" amend to "wind forces";
Line 529: suggest to modify "In this study we demonstrate the" to "In this study, we demonstrate the";
Line 534: suggest to modify "that was previously observed" to "that were previously observed" "; Conclusions
Line 565: suggest to modify "In this work we address dynamics of" to "In this work, we address dynamics of";
Line 573: suggest to modify "have different structure" to "have different structures";
Line 578: It is recommended to modify "numerical modelling" to "numerical modeling";
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
General comments:
The authors analyse the response of rivers plume to coastal sea circulation inferred from aerial drones’ imagery, which is interesting. The study demonstrates also the potential of aerial remote sensing in observing internal waves signature and identifying mechanisms of their generation. The subject addressed is within the scope of the journal. The paper seems to present novel results, and convincingly conclude on how the energetic features of coastal circulation can influence locally and during short-term periods the dynamics of small plumes. However, the manuscript requires some modifications before being suitable for publication:
- The motivation for the study should be better presented. For instance, the reasons of choice of the two rivers as case studies to investigate the spatial and temporal structure of the buoyant plumes are lacking.
- The innovative aspect of the work is lacking in the abstract and was poorly presented in the introduction. In the former manuscript, the novelty of the work is hidden in the discussion.
- The text is understandable, but the English has to be improved. Some sentences are too verbose and often leading to unclear meaning of the sentences. There are many typos, so I recommend for the authors to carefully read the revised version and avoid mistakes.
Specific comments:
Title: The former title uses the term “temporal variability”. This implies short- and long-term variability whereas in the study only short time scales are reported. A suggestion for a more concise title could be: “Spatial structure and short-temporal variability of small river plumes as observed by aerial drones”
Line 18: Yes, but not in all conditions as mentioned on lines 61-63. The limitation of drones usage should also be briefly reported in the abstract.
Line 20: For clarity, please add “short” temporal variability.
Line 22: For clarity, please split the sentence in two after “plumes”.
Line 24: Replace “the front’’ by “a front”.
Line 26-28: This sentence is confusing and needs rephrasing. Possibly: “The results reported in this study are addressed for the first time as previous related works were mainly limited by the low spatial and/or temporal resolution of in situ measurements and satellite imagery”
Line 28: Therefore, aerial drones “could be efficient tools used to obtain qualitative insights of the structure ....”
Lines 65-66: Why those two rivers were chosen as case studies to investigate the spatial and temporal structure of their buoyant plumes? This information needs also to be brought in the first paragraph of the intro and the abstract!
Line 66: “.... northeastern part of the Black Sea”. Point the reader here to Figure 1 which shows the location of the area)
Line 67: It is rather “short” temporal variability. In the previous sentence drones’ limitation of flying less than several hours was reported.
Line 73: Replace “of” by “derived from”
Lines 74-75: Sentence doesn’t quite read right. Rephrase for clarity please!
Lines 77-105: Section 2.1 should be merged with the introduction as the Bzyp and Kodor rivers are introduced as case studies. Shortening where possible is also recommended here.
Line 104: Seems that the word “is” is missing just after “seas”.
Lines 115-116: Indicate on a map where the in-situ measurements were made.
Line 117: Indicate the weather station location on a map.
Line 119-121: The fact that aerial observations and field work at the Bzyp plume were not made during the same period (season?), shouldn’t that affect the conclusions?
Line 129: The weight function should be explicitly stated here.
Section 2.3: Having a chart describing the aerial data processing would help see better the steps taken to calculate the surface velocity fields.
Lines 140-142: It would help to indicate where the eddy features and the lobe-cleft structures area on a map (like on Figure 1 or 2).
Line 165: shouldn’t Figure 2 be Figure 3?
On Figure 2, add regression lines and correlations coefficients with p-values! The correlations and their significance are not indicated anywhere!!
Line 154: How the extents of the plumes were calculated?
On Figure 4, 5, 6 and 15: Add on panels (a) to (d) P1, P2, … instead of just 1, 2.... On their captions, change color to coloured.
Lines 201-203: Was the rainfall information derived from the weather station? or was it based on the literature? Specify please.
Line 223 and 225: Here and elsewhere in the manuscript, please add “psu” after indicating the salinity values.
Line 225: Figure 6b is mentioned but it seems that 6c is the correct panel here
Line 227: Figure 6c is mentioned but it seems that 6d is the correct panel here
Line 222: This low-turbid zone “contrasted especially”
Line 238-248: This paragraph is exactly the same as the previous one. Please remove it.
Line 283: Here and elsewhere in the manuscript use observed ‘by’ satellite imagery and not ‘at’.
Line 291: The sentence doesn’t quite read right. Needs rephrasing. Possibly: “The sizes and the anticyclonic rotation in the northwestward direction were similar for eddies detected at the Kodor plume by aerial and satellite remote sensing.”
Line 323-324: The statement is unclear and confusing. It needs rephrasing, so the figure can be better understood.
Line 466: we describe ‘the’ formation
Lines 459-469: This paragraph wrap up nicely the main conclusions derived from Section 3. Thus, the recommendation here is to move it as the last paragraph of section 3 and start the discussion from the word ‘Below’ at line 469.
Line 477-479: Consider splitting for more clarity.
Lines 518, 521-522, 530-532, 541-543: these lines report important results and their main message should be highlighted in the abstract!
Line 564: add a statement here on the limitation of the drones’ usage.
Line 577-579: Rephrase please. “More detailed work on the small plumes revealed features requires specific ......”
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 3 Report
Review of the paper: “Spatial structure, temporal variability, and dynamical features of small river plumes observed by aerial drones".
In this paper a very interesting and important theme of research of the inflow of smaller rivers into the world's seas and oceans was analyzed. The methodology of aerial/satellite imaging and simultaneous instrumental measurements in river plumes is promising and may lead to new results in estimating the spatial and temporal variability of river flows entering seawater.
The construction of the paper is good and correct. The suggestions bellow have the purpose to contribute with the authors.
My general comments and suggestions are as follows:
- INTRODUCTION
In this chapter the authors provide a nice information about the main topics of their work. My suggestion is to describe the main goals of the work after line number 69.
- DATA AND METHODS
Terminology: authors use terms shore (shoreline) and coast (coastline). Generally the terms are synonymous.
In the paragraph between lines 95 and 105 the authors describe the features of the coastal circulation. Is it surface and/or subsurface circulation?
Chapter 2.2 describes the methodology of observation and measurement, but no in situ measurement positions are given. It should be added that the positions (lines/transects) of the individual measurements are given in Chapter 3, for each individual measurement.
Lines 194-196. How can it be concluded from Figure 4c that downwelling is registered?
Paragraph between lines 238 and 248 is copy-paste of the paragraph between lines 219 and 230!
Line 313. It is quoted Figure 9a. But, is it Figure 9b?
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
Please find the attachment.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.docx
Reviewer 5 Report
This research is very interesting, but still needs to be improved for two points:
1) The last paragraph should be the aims of this study rather than the structure of other sections. Please rewrite it;
2) Validation should be mentioned in Results or somewhere?
Author Response
Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
1) General comments
After the author's revision, this research has been dramatically improved, and the manuscript is more precise and complete.
Generally, the structure of this investigation is clear and easy to follow. However, the writing of the manuscript requires a lot of English editing, and there are many errors in grammar, spelling and sentence structure. I have provided some suggested changes in the "specific comments" below to improve this situation. With significant modification, this study has the potential to be an interesting contribution.
2) Specific comments
Abstract
- There is no need to go into details in an abstract. Please pay more attention to solve these and the main findings and conclusions obtained, so a modification is needed.
Introduction
- No scientific and reasonable hypotheses are made, making the text too descriptive. The hypothesis should be established and tested through observations, and the hypothesis should be demonstrated point-to-point around the research purpose, and finally, the problems solved and significance of the research should be summarized.
- Line 43-45：suggest that "[e.g., 31, 32]", "[e.g., 33 – 35]", "[e.g., 36 – 38]", "[e.g., 39 – 41]", "[e.g., 42 – 44]" and "[e.g., 45 – 47]" be changed to "[31-32] ", "[33-35]", "[36-38]", "[39-41]", "[42-44]" and "[45,47]", respectively.
- Figure 1：I suggest that the author split the "introduction" into "introduction" and "study area".
Data and Methods
- Line 183：suggest that "user" be changed to "use".
- Line 189：I suggest that the author put the formulas on a separate line, and number them first to last.
Results
- Line 234：suggest that "deep" be changed to "depth".
- Figure 2：I suggest the author to explain what the correlation coefficient (r) and p-value mean.
- Figure 3：I suggest the author to state the acquisition time of the aerial image in Figure 3.
- Figure 8：Please explain why the Sentinel-2 image is out of sync with the actual measurement.
- Line 412-413：I suggest that the author use figure to show the difference in internal wave propagation between aerial imagery and satellite imagery.
- Figure 9：Please explain why the images used to monitor internal wave propagation in Kodor and Bzyp plumes are inconsistent. Kodor plumes use aerial imagery, while Bzyp plumes use satellite imagery.
- Line 526：I suggest that the author put the formula on a separate line and number it.
Discussion
- The discussion section is too descriptive, please pay more attention to revealing the formation mechanism of Kodor and Bzyp plumes, variability and dynamics.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 2 Report
The authors seem to have responded to most of the reviewer feedback. The reviewer had asked to highlight the motivation of the study and its innovative aspect along with other methodological corrections. The authors did that to some extent and replied (in their feedback) about 'limitations of the study'.
The remaining minor point not fully addressed is the working title, which the authors agreed to change in their point by point responses but left it unchanged in the actual manuscript. Hopefully, they will update it in the next version.
Author Response
Please see the attachment
Author Response File: Author Response.docx
