Review Reports - Determination of Accurate Dynamic Topography for the Baltic Sea Using Satellite Altimetry and a Marine Geoid Model

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Dear Authors, I am happy with the changes you made to this manuscript. Everything is clear now; and your intentions, methods and results are well described. You have also added important references about the model. Well done. I recommend this manuscript for a publication in a present form.

Author Response

Thank you very much for your approval and also the previous comments and suggestions which made the paper more understandable for the readers. We would like to take this opportunity to also thank you for the effort and expertise that you have contributed towards reviewing this manuscript which helps maintain the high standards of the Remote Sensing journal.

Reviewer 2 Report (Previous Reviewer 2)

The authors took into consideration my comments to the original version of the manuscript, provided some more details on their study. That improved the manuscript and, at the same time, made it even more extensive, as before. I still have the following comments that should, from my point of view, be taken into consideration before a decision on the acceptance of the manuscript can be made.

General comments

1. The title of the manuscript does not correspond to its content. Since the authors do not seem are going to publish the new dynamic topography for the Baltic sea developed by them, but just present a new method to derive this topography and discuss in details problems in the data they use for that, an appropriate title of the manuscript can be, for example, as follows: “On the Determination of Accurate Dynamic Topography for the Baltic Sea using Satellite Altimetry Data and a Marine Geoid Model”.

2. I would strongly suggest that the authors publish the dynamic topography of the Baltic sea derived within this study, i.e. make the data publicly available, not just on request, but permanently. In this case, the original title of the manuscript would correspond to its content.

3. While reworking on the manuscript, the authors added new citations. However, there are too many self-citations: totally 15 of 50 references. This does not make an impression that the authors are very familiar with the work of other authors in this field. For examples, using references to text books, review articles or papers of other authors would be more suitable in lines 30, 70, 89, 98 and some others then self-citations, since these self-citation papers are, to my understanding, not the pioneer works on the subjects they support.

4. English of the manuscript should still be improved. I made some suggestions below. However, they can be not complete. Some sentences and parts of the manuscript are difficult to understand. The authors put very often the object before the subject without putting a comma after the object. I suggest to carefully check and improve English of the manuscript, may be, by a native English speaker or to use special services offered by publishers.

Specific comments

Line 47: “determining of both” should better read “determining both”.

Line 50: “A secondary aspect is that this study examines is” should read “A secondary aspect that this study examines is”.

Lines 56: “requires the utilization”. A subject is missing in this part of the sentence, e.g., “one requires the utilization”.

Lines 61, 129, 153, 182, 188, 653, 686: I would put a comma before and after the word “however”.

Line 63: “An example is illustrated” should read “This is illustrated”.

Lines 75, 771: a comma is missing before “whereas”.

Lines 79-80: “either with the geoid, HDMs , TG and SA datasets” should read “either with the geoid, HDMs, TG or SA datasets”.

Lines 118-119: “allows a logical inter-comparison to be performed”. Again, a subject is missing, e.g. “it allows a logical inter-comparison to be performed”.

Line 123: “For more detailed understanding into these sources more” should read “For more detailed understanding these sources, more”.

Lines 125-126: “other sources … consists” should read “other sources … consist”.

Line 132: “TG network;” should read “TG network,”.

Line 134: “In particular the, HDM bias” should read “In particular, the HDM bias”.

Lines 139 and 802: “along track” should read “along-track”.

Line 145: “demonstration” should better read “development and demonstration”.

Line 165: “Once this is performed the HDM data” should read “Once this is performed, the HDM data”.

Lines 168 and 177: “SA computed” should read “SA-computed”.

Line 169: “TG observed” should read “TG-observed”.

Line 178, 301, 471, 595, 682, 774: “SA derived” should read “SA-derived”.

Line 178, 197: “HDM derived” should read “HDM-derived”.

Lines 179-181: English in this sentence should be improved, in particular, in the part starting from “for it is a model with its limitations”.

Lines 181-182: English of the following sentence should be improved: “The HDM however is still a key source for it simulates both coastal and offshore sea level data.” It is not clear to which subject the verb “simulates” refers.

Line 184: a comma is necessary before “it can be compared”.

Line 224: “between HDM” should read “between the HDM”.

Line 225: “as combination” should read “as a combination”.

Line 235: “the closest location”. Please specify, the closest location to what.

Line 282: “at each side of the coast then only one” should read “at each side of the coast, only one”.

Line 294: “then a bilinear interpolation” should read “a bi-linear interpolation”.

Line 398: “However” should be followed by a comma.

Line 420: “are spelled out” should better read “are given”.

Line 430: “harmonized” should read “are harmonized”.

Line 439: “they are required” should better read “their measurements are required”.

Line 451: “Figure 4 shows the steps” should read “Figure 5 shows the steps”.

Line 458: “Institutes-” should read “Institutes”.

Line 459: a comma is necessary after “In this study”.

Lines 469-470: “HDM, that can now use” should read “HDM is described, that can be now used”.

Line 485: a comma is required after “In the figure”.

Figure 6b: please specify a unit in the Y axis.

Figure 6: I would suggest to arrange the subplot in the following order: a), b), c). Presently, it is in the order: b), a), c).

Line 492: “inFigure 4(a) also in Table A1” should read “in Figure 4(a), also in Table A1”.

Line 493: a comma is required after “From Figures 6(b) and 6(c)”.

Lines 493-494: “This figure indicates” should read “Figure 6(c) indicates”, since the previous sentence mentions not one, but two figures.

Lines 493-496: “This figure indicates that the maximum discrepancies of HDM (~30 cm) occur from February to March (winter-spring) and the smallest during autumn and summer seasons (less than 20 cm).” Can you, please, explain, why?

Line 501: a comma is missing before “also”.

Line 514: “The NKG2015 model used” should read “The NKG2015 model was used”.

Line 543: a comma is missing before “it uses a leading-edge”.

Lines 555-556: “gross errors and outliers.” Please explain in the manuscript, what is the difference between gross errors and outliers.

Line 563: a space is missing between “ITRF” and “(realization 2008)”.

Line 564: a space is missing after “ETRF”.

Line 564: “Also, recall” do not need a comma.

Line 573: “These steps are illustrated in Figure 7.” In fact, this is figure 8.

Line 599, 650, 679, 680, 687, 776, 788, 805, 931-932, 943: a comma is required before “where”.

Line 604: A comma is missing after “In this figure”.

Lines 635-636: “to validate different SA mission” should better read “to validate a different SA mission”.

Lines 649-650: “illustrate an example” should read “illustrate”.

Line 653: “appears larger” should read “appears to be larger”.

Lines 654-655: a comma is missing before “it can reveal”.

Line 667: “in general” requires a comma before and after it.

Line 673: “passes #158,272” and “passes #169,283,37”. A space is required between a comma and a number in all three cases.

Line 674: “hints of the problem” should better read “hints that the problem”.

Line 684: “latitude 54°” should read “latitude of 54°”.

Lines 688-690: English should be improved.

Line 701: a comma is missing before “a negative deviation”.

Line 704: “HDM modelling problems or SA” should read “HDM modelling problems or SA problems”.

Line 710: a comma is missing before “a large deviation”.

Lines 607 and 711: “TG corrected” should read “TG-corrected”.

Line 716: “at this area the Swedish TGs” should better read “the Swedish TGs at this area”.

Line 740: “Equation (110)”. There is no such an equation. Please check the number.

Line 742: a space is missing before “2017-2019”.

Lines 747-747: English should be improved in the text: “are determined by black dots the mean and RMSE”.

Line 748: “STD larger than” should, most probably, read “larger than”.

Lines 763-764: “therefore in the winter months it may be challenging for SA to track the sea surface correctly”. I would write this as follows to make it clearer: “therefore, it may be challenging for SA to track the sea surface correctly in the winter months”.

Line 775: “JA3 associated” should read “JA3-associated”.

Line 783: “Examining figure 12, also shows” should read “Examining Fig. 12 also shows”.

Line 785: a comma is missing after “For this particular area”.

Lines 787-788: “showed for the Swedish western coast the largest residuals of around 25 cm existed” should better read “showed the largest residuals of around 25 cm for the Swedish western coast”.

Lines 793-794: the following sentence is just a duplication of the previous one and should be erased: “For truthful identification further investigation would be necessary and this can be performed for future studies.”

Lines 796-797: a comma is missing before “the standard deviation appears to be”.

Lines 798-799: “a persistent pattern the black dots show”. English should be improved.

Line 809: a comma is missing before “the SA passes cross”.

Lines 818-820: English, the order of sentence parts should be changes as follows:

“In Figure 12 (a)-(c), large discrepancies ΔDT SA−HDM within the range of 30 cm are observed at latitudes 59.6° around the western coast of Finland and in the eastern Gulf of Finland.”

Lines 825-827: English should be improved.

Line 833: “the S3A and JA3 mission” should read “the S3A and JA3 missions”.

Line 835: “The normalization has been calculated” should better read “The normalization has been performed”.

Line 838: “black dots location in Figure 12(e)” should read “black dots locations in Figure 12(e)”.

Line 838: “that they are” should read “since they are”.

Line 862: “large residual (HDM-TG)”. Is it just one residual (“a large residual (HDM-TG)”) or many of them (“large residuals (HDM-TG)”)?

Line 872: “in right axis” should read “in the right axis”.

Lines 877-878: the words “within latitudes 59.6° to 60°” should be moved at the end of the sentence.

Line 881: “in middle of the sea” should read “in the middle of the sea”.

Line 881-883. It is better to split this sentence in two sentences.

Lines 882, 947, 985: “geoid related” should read “geoid-related”.

Line 884: “SA tracks approaching” should better read “SA tracks approach”.

Line 885: “S3A is less scattered” should read “S3A data is less scattered”.

Line 889: “multi missions” should read “multi-mission”.

Lines 895, 904, 909, 923, 930, 931, 939, 951: article “the” is missing.

Line 912: “location dependent” should be better written as “location-dependent”.

Line 923: “SA orbit inclination” should read “satellite orbit inclination”.

Line 957: “lead to improving”. Do you mean “lead to the need to improve”.

Line 968: “commentary data”. Do you mean “complimentary data”?

Line 973: “A core component utilized that made this possible was access”. English should be improved.

Line 976: A comma should be added before and after “on average”.

Line 990: “solves better the signal”. Do you mean “resolves better the signal”?

Line 1014: “institute” should be plural, since the following list contains four institutes.

Tables A2 and A3 bring, from my understanding, no important information for understanding this study and can be erased to save the space or can be put into an electronic supplement to the paper.

Author Response

Thanks for your comments, please refer to the attached file for the specific replies.

Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Reviewer 2 Report

The manuscript aims to develop an accurate dynamic topography using satellite altimetry and a marine geoid model for the Baltic Sea. The authors describe in details their methodology and datasets used. From the analysis of these data, they found many deficiencies in the geoid, tide gauge, hydrodynamical model and satellite altimetry data they use and try to interpret these deficiencies. Some of them seem to be related to drawbacks of the methods used near the coast. Other seem to be related to the fact that some of these methods do not perfectly work for ice-covered parts of the Baltic sea in winter. Use of other methods seems to be degraded by a presence of many small islands in the sea. So, from this paper, there is still a room for improvement to derive an accurate dynamic topography for this sea from the data used by the authors to what the authors draw attention in their paper. The paper is rather good written, reasonably structured, contains many discussions not just in a dedicated section, but also in previous ones. I think, the manuscript can be considered for a publication after the following comments are taken into consideration.

General comments

1. I am not sure that the title of the paper is suitable. Since the authors, to my understanding, do not publish a new accurate dynamic topography, but rather draw attention to many inconsistencies or possible errors in the data that they use and methods they apply and they restrict their investigations to the Baltic sea, I suggest the following title: “On the deficiencies of the geoid, tide gauge, hydrodynamical model and satellite altimetry data for the Baltic Sea”.

2. Please provide references to support the statement on the necessity of correction of tide gauge records for vertical land motion (lines 64-65). It is not sufficiently clear described, how that was done for the tide gauge data used in this paper. Please, provide more details. Have you used any data, from, e.g., any of four solutions available at SONEL (https://www.sonel.org/-Vertical-land-movements-.html?lang=en)? If so, please, specify from which one and provide a reference.

Specific comments

Lines 12, 119 and many others cases: “along track” and “along-track”. Please check the correct way of writing in the whole manuscript.

Line 15: please explain the abbreviation RMSE at the first use.

Lines 28-30: please provide a reference (references) to support this statement.

Line 38: please explain the meaning of the word “sub-mesoscale”.

Line 84: the words “coincide with the coordinates” should read “coincide with the reference frame of the coordinates”.

Lines 94-95: please provide a reference for the Baltic+SEAL project already at this place, even it is given later.

Lines 109-110: a verb should be added in the text “a high-resolution geoid model and access to data as-similated HDM and SA data specifically tuned to the sea conditions”. Otherwise, it is not clear.

Line 161: please change the order of Fig. 2(b) and Fig. 2(a), since you cite first Fig. 2(b).

Line 167: a comma should be added before “i.e.”.

Line 211: “reflect” should read “reflects”.

Lines 219-221: please check the use of single and plural form of the verbs in the sentence “As a result, …”

Line 229: Do you take into consideration any corrections for the pulse propagation through the atmosphere? If so, they should be described here.

Line 237: “By applying dh,”: please describe, how dh is computed or comes from.

Lines 247-248: “1.5m” and “~1.3m” should be written with a space before “m”.

Line 271: “The location” should read “The locations”, i.e. in plural form.

Line 291: “The Baltic Sea is the world's second largest brackish water body...”. After what? What is the largest one? Please, add.

Line 325: “HDM models” should read “HDMs”, since M in HDM stands for “model”.

Line 398: “also in TableA1” should read “and also in Table A1”.

Line 407: a space should be added before and after the text “(more than 9 cm)”.

Line 422: “due to poor coverage” should better read “with the poor coverage”.

Line 430: “tracks geometry (Figure 6)”. I suppose, you mean here Figure 7.

Line 437: “Jason 3” should read “Jason-3”.

Line 441: please provide a reference (references) to support the statement “In this study, the ALES+ retracker SA data products for the JA3 data and ALES+SAR for S3A and S3B are used.”

Line 444-445: the text “This retracker use” should read “This retracker uses”.

Line 448: “The Baltic+SEAL consists of” should better read “The Baltic+SEAL provides”.

Lines 450-451: “The data products consist of employed...”. Do you mean that “The data products are based on the use of…”?

Line 466: “Topex/Poseidon” should read as “TOPEX/Poseidon”.

Line 467: please specify, which exactly ITRF realization and explain the meaning of ETRF.

Lines 493-494: “measurements gross errors and outliers”. What is the difference between gross errors and outliers? Is it not the same? Anyway, no values are shown in Table 3 for gross errors. I suggest to eliminate the words “gross errors”.

Table 3: I am not sure that “phi” and “lambda” are needed in this table.

Lines 506-507: “In this figure cycles 18, 21 and 26…” This sentence should be improved. One can’t compare cycles with dynamic topography.

Line 509: the text “(a)” should be placed just before “Comparison of S3A pass…”.

Line 517: “seasonal variations in DT” should read “seasonal variations in DT observed”.

Line 523: a space is missing before “about these”.

Line 538: “The pass number” should read “The pass numbers”.

Lines 541-543: the sentence “The gray areas represent…” partly repeats what is written caption of Fig. 10.

Line 550: “green shade” and “green shade”. Green shade and purple shade regions are hardly visible in Fig. 10.

Line 554: “respect to” should read “with respect to”.

Line 557: “data-corridor” should read “data corridor”.

Figure 11: What is shown by dashed and solid lines in Fig. 11(a) and Fig. 11(b)? Please explain. Sub-figures (c) and (d) should be numbered.

Lines 571 and 572 should be in the same paragraph, as the lines 560-561.

Line 576: “Figure 11(d), (e), (f)”. Do you mean “Figure 12(d), (e), (f)” here?

Line 577: “more than other locations” should read “more than for other locations”.

Lines 580-581: English should be improved in the sentence “Note that the method employed the TGs records for correcting HDM is quite robust.”

Figure 12: please increase the font size of the numbers and letters of both color bars. They are too small.

Line 609: “20cm” should read “20 cm”.

Line 618: there is no need for a new paragraph. This text is a continue of the text of the previous line.

Line 652: “exists” should read “exist”.

Line 659: “This model produced by” should read as “This model was produced by”.

Line 664: “during winter seasons” should read “during the winter season”, since 6 months can cover just one winter season, not many.

Line 676: “The Figure 14(a) and (b) identifies” should read “The Figures 14(a) and (b) identify”.

Figure 14: the quality of this figure should be improved. Some its elements are not sharp enough.

Line 722: “the moving average 0.5° (blue line) appear” should read “the moving average of 0.5° (blue line) appears”.

Line 730: “hence there” should read “there”, since there is the word “Since” in the first part of the sentence.

Line 755: “leads” should read “lead”.

Line 759: “there still” should read “there is still”.

Line 790: please put a point at the end of the sentence.

Line 830: “altimetry mission; Sentinel-6 Michael Freilich satellite” should read “altimetry mission, Sentinel-6 Michael Freilich satellite,”.

Lines 842: I suggest the authors to make publicly available the post-processed satellite altimetry-based sea level data as well as the accurate dynamic topography from the present study.

Lines 856-862: I suggest to move the complete Appendix A to the electronic supplement to the paper, if it is foreseen by the journal. If not foreseen, just Tables A2 and A3 can be, from my point of view, erased, since they are too technical.

Lines 863-994: please add DOI or web links to a few references for which they are still missing. Please use consistently either a full of short way of journal names.