Enhancing Regional Quasi-Geoid Refinement Precision: An Analytical Approach Employing ADS80 Tri-Linear Array Stereoscopic Imagery and GNSS Gravity-Potential Leveling
, Gang Chen 1,*, Defang Yang 2,3, Kaihua Ding 4, Rendong Dong 5, Xuyan Ma 2,3, Sipeng Han 1,6, Shengpeng Zhang 7,8 and Yongyin Zhang 8Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors of the manuscript “Enhancing Regional Quasi-Geoid Refinement Precision: An Analytical Approach Employing ADS80 Tri-linear Array Stereoscopic Imagery for Aerial Triangulation Densification and GNSS Gravity-Potential Leveling” present a method for improving the regional quasi-geoid model using airborne photogrammetry and GNSS measurements.
The Introduction Section starts with the sentence “The quasi-geoid is derived from the geoid”. In my opinion, I think that this quantities (quasi-geoid and geoid) should be defined, and it’s better saying “quasi-geoid undulation” and “geoid undulation”.
The authors use often the expression “satellite gravity model” to refer to global gravity model (GGM)as EGM2008, EIGEN-6C4 and so on, that are models based on satellite data but also on ground-based gravity data. All the GGMs are based on satellite observations, that are fundamental at least for the first degrees of the spherical harmonic development. So, the term "satellite" is used especially to emphasize when the GGM model is only based on satellite observations.
I'm not sure to correctly understand Fig. 10 from (b) to (m), could you explain better the meaning of those plots?
The models represented in Fig.11 do not seem to be represented in the best way: in my opinion a standard 2D plot would be better, with the same color scale. Furthermore, Fig.11b reports negative values ​​of the effective values, but this is not possible. Is it a graphic distortion? An analogous problem in Fig. 9 and 12
Minor remarks:
Figure 7: define what “JCP” is
Line 90: “Therefore, Therefore, this” —> “Therefore, this”
Line 765: “levels: For” —> “levels. For”
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsREVISION MANUSCRIPT remotesensing-3102701: “Enhancing Regional Quasi-Geoid Refinement Precision: An Analytical Approach Employing ADS80 Tri-linear Array Stereoscopic Imagery for Aerial Triangulation Densification and GNSS Gravity-Potential Leveling.”
Specific comments:
Comment 1: The abstract and introduction do not mention anything about InSAR and the reason to be applied.
Comment 2: The statement (lines 80-82) “In recent years, due to advancements in positioning accuracy achieved by integrating data from the four major global satellite navigation systems, GNSS-measured geodetic heights have attained a precision level in the millimeter range” it requires a reference.
Comment 3: Resolution of Figure 3_c and 3_d (lines 303-304) needs to be improved.
Comment 4: The Section 2.2 was named as Acquisition and Processing of GF2, GF7, and Sentinel-1A Imagery, however, it does not present a deep description about Sentinel-1 images or InSAR. It is recommended to add information about the InSAR processing, for example: software, temporal baseline, reference point, type of images, etc.
Comment 5: In Section 3.1, the authors mentioned "The outcomes reveal the time-series deformation rates and quantities for the Line-of-Sight (LOS) (Figure 3c)", however, Figure 3c is the interferogram network.
Comment 6: In Section 3.1, the author mentioned "An analysis of Figure 3a, and 3b indicates that the overall deformation in the study area fluctuates between -5mm and 4mm", however, the Figure 3 shows a different range.
Comment 7: In Section 3.1, it is not clear when the authors are talking about cumulative displacements in the vertical or LOS direction.
Comment 8: In Section 3.1, it is recommended to add the velocity (mm/year) of the area of interest. Also, include the spatial and temporal coherence (to understand the quality of the results).
Comment 9: What is the accuracy of the national first- and second-class leveling lines?
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis paper is a resume of an investigation into Enhancing Regional Quasi-Geoid Refinement Precision for a defined area of the Qinghai-Tibet plateau.
The Abstract is well written and is a fair synopsis of the paper. I am sure that the authors are as fulsome as possible with their title, but I think it should be shortened. It need not go beyond the first line though it could include something like for a defined area of the Qinghai-Tibet plateau or something like that. The rest of the paper’s title is already outlined in the Abstract in any case.
The paper is a challenging read, at least for this reviewer but it appears to be underpinned by sound literary and mathematical principles. However, there is the uneasy feeling that the authors have attempted to cram an entire project into one paper and, if correct, they do themselves a disservice as it seems clear there is more than one paper in this project. Perhaps others have been published previously?
The paper includes numerous Figures with improper captions. The captions seem to include a discussion of the content of the Figure. A single line caption is more appropriate, and the discussion moved to the main body of the text. The Figures should also be as uncomplicated as possible and do the authors really need so many? Often the Figures have captions that are barely discernible at print level.
Some finer detail. Line 182, should the surveyed area dimensions not be the other way round? Considering Figure 3 that assigns six colors to ellipses but there appears to be only five ellipses. Also, consider if yellow against a white background provides a good contrast. From page 9 onwards there are sections that would be better moved to the Methods and Materials section. Line 356 refers to circular triangles. Just for clarity, are the authors referring to Reuleaux triangles as the symbols used by the authors don’t seem to resemble circular triangles?
Could the authors please clarify what they mean by coordinate stabbing? Are they talking about a least squares transformation?
With respect to Figure 8, the authors refer to black dots that correspond to the actual POS points calculated post flight. There does not appear to be any black dots, or at least none that this reviewer can see.
I trust the authors find these comments helpful. Their expertise is not in doubt but a more succinct approach would be helpful and commend the study to a wider audience.
Comments on the Quality of English LanguageAll things considered the quality of English is fair even if a little longwinded.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsI would like to thank the authors for their responses to my questions. The revised manuscript is improved, but I still have to raise the issue of negative RMSE values.
The term RMSE is usually understood as Root Mean Square Error and as such cannot take negative values. By your answer in the cover letter I understand that you are referring to the residuals values, that can assume negative values. Is it correct? However, In Figure 9 the two quantities (residuals and RMSE) are clearly represented, but in fig. 12 the authors affirm the values on the plots (also negative) are called RMSE, instead of residuals
Moreover, the different ranges in the scales of Fig. 12 do not help to compare the results.
Minor remarks:
Line 539 and Line 589: “satellite gravity mission” —> “gravity geoid model”
Line 596: “satellite gravity mission” —> global gravity model
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThanks to the authors for their thorough revisions and additional explanatory content. They may wish to consider shortening the caption of Figure 3 but this is a minor detail and is not a barrier to publication of course. The responses in the covering letter were very helpful.
Author Response
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Author Response File: Author Response.pdf
