BDS-3 Time Group Delay and Its Effect on Standard Point Positioning
Round 1
Reviewer 1 Report
Review Report of “BDS-3 time group delay and their effects on positioning” by Dai et al.
General Comments:
This paper illustrates the advantage of using BDS-3 demonstrating the effect on the site positions with and without time grouped delay correction. The results and the conclusions of this study are very important for the ongoing development of BDS3 system. A well organized and well-written manuscript would be a very good contribution to science.
I enjoyed reading the introduction, methods and processing strategies section. Although there were some grammatical issues and referencing issues (tables were not cited properly), each section provided adequate background information.
However, while I was reading section 4, I found that this section might confuse the reader.
The readers may find “horizontal position error scatter plots” and “vertical position error scatter timeseries” figures redundant. In many places, the authors did not even discuss some figures. For example, figure 2 and 3 were never discussed in the text. If these figures are important, please discuss the notable features that readers should look for, and walk the readers through those, one by one. As, I mentioned that if there are no important or interesting features or showing redundant information, please move them into a supplement. I actually think that a figure with bar plots for the improvements for all stations and all signals would have been very useful, which would have replaced the tabular information presented in, for example, table 5. Also, averaging the RMS for all stations may not show real improvement. That said, if one or two stations are too bad, the contribution from the better stations may not reflect the improvement properly. Please show the improvement for all stations. Same comments for (4.2) BDS-3, (4.3) BDS2 + BDS-3.
Also, table 5, 6 and 7 are showing the same information but the format of the tables is not consistent. Please make those consistent.
Regarding the language issue, this manuscript needs to go through rigorous language editing. I suggest that authors revise the manuscript and correct for grammatical error and improve the quality of the sentences.
The results and conclusions look promising. However, my concern is that since this paper is full of information, the authors need to summarize and present these in a consistent manner. I think this paper will be publishable after a major revision.
Some Specific Comments:
Abstract:
Line 16 – 18: Mention the frequency for B1, B2 and B3 signal.
Line 25: B1I “and” B3I?
Line 30: “ ….. the up component increased relatively little”. Please provide a quantity.
Introduction:
1. Line 39: Please elaborate “PNT” since this is the first instant.
2. Line 45: “…. expected to provide global service with 5 GEO, 3 IGSO and 27 MEO satellites at 2020”. Please use “by” instead of “at”.
3. Line 49 – 51: Please rewrite this sentence.
4. Line 45 – 54: Are they two different sentences? Please rewrite this for clarity.
5. Line 55 : Insert “by” after the word “investigated”.
6. Line 97: Insert “of” after “combinations”.
7. Line 125: What is the source of Broadcast Ephemeris for BDS-3 Satellites?
8. Table 1 and 2: Reader may find it confusing that the tables were not cited in the text. These two tables can go in the supplement if they are not contributing significantly in the text.
9. Line 192 -193: Readers may get confused here. I think the authors have to describe the features shown in each and every figure so that readers can follow and justify the conclusions that were made in the following lines. If there is no important feature in those figures, remove them from the main text and keep them in the supplement.
10. Line 193: What are the different schemes?
11. Figure 2, 3, 5, 6 and other similar figures: Make the x and y-axis one to one.
12. Line 251 – 261: Same comment as for line 192 -193.
Author Response
Thank you very much for your encouragement and comments. We have revised the manuscript carefully and responded point by point to the comments at attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper is well structured. The used methodology well described, as the performed analyses and results, that are very interesting and useful for practical applications.
Some mispelling and English grammar errors are present in the text (some indications are given in the attached reviewed file).
Easting and Northing components are often switched between each other in the description, results and Figure captions (see attachment).
The Authors can better explain the criterion used for choosing particular days in the 41 set for some analyses.
Comments for author File: 
Comments.pdf
Author Response
Thank you very much for your encouragement and comments. We have revised the manuscript carefully and responded point by point to the comments at the attachment. Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
I have serious concerns about the whole structure of this manuscript and its conclusions. It contains bewildering thoughts cluttered here and there. No crystal clear message is given as to what is the purpose of this paper, why this investigation has been carried out (why do you have to analyze the time group delay in this investigation? What was the impetus?) and how this investigation has been done. This is not clear at all in this manuscript. The reader has to fish out what the authors wish to pass onto their readers.
No explanation has been provided if and how outliers are treated when presented in positioning error diagrams. Does for example the calculation of the root mean square error contains outliers or these have been screened out in the process? These are not explained in the manuscript. That is fundamental as it may change conclusions of this work immensely.
No explanation or justification has been provided as to why certain patterns and trends of data are shown on the Diagrams (Fig.3, Figs.10, 14, 17, 19, etc.).
Authors inject opinion without supporting statements. For example “With the rapid development of the BDS-2 constellation, BDS-2 become a hot topic in GNSS application community.” This is an unsupported statement without backing it up. See also “Until now, BDS-3e has been analyzed by many experts and scholars.” and “We surmise this may be attributed to the noise is magnified in dual-frequency SPP scheme” (based on what evidence?) Personal opinions do not have a place in a scientific paper.
All diagrams in this manuscript should label their axes clearly. Do not provide a description in the label below only.
Statistical terms such as “variance factor” are not used in the correct sense.
Models such as that of “Klobuchar” are mentioned without any reference.
Title and manuscript have serious grammatical and structural mistakes. This manuscript cannot be published as it stands now. It may contain gems of research work but the way it is presented does not show this. Parts of the manuscript do not make sense at all. I suggest the authors give their manuscript to some whose mother tongue is English to correct it.
All titles in the Tables and Figures are not self-explanatory. Sometimes they do not make any sense.
The manuscript is inundated with abbreviations. Abbreviations are defined several times, even defined in the keywords. The gist of the message of this manuscript is lost and it does not pass upon the readers. No abbreviations should be spelled out and used in abstracts and in keywords.
Numbers, less than 10, should be written in full.
References in the manuscript are not shown. The message “Error! Reference source not found” appears several times throughout the manuscript. References at the end are not written correctly.
Author Response
Thank you very much for your encouragement and comments. We have revised the manuscript carefully and responded point by point to the comments at the attachment. Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The paper has been substantially improved and now addresses most of my concerns. Now, I would recommend it for publication.
Author Response
Thank you very much for your encouragement and comments.Reviewer 3 Report
Authors have tried to respond to my requests although part of their responses are still outstanding. The manuscript has been improved although it has not reached a level and quality to be accepted to the Remote Sensing Journal.
I still have serious concerns about this manuscript and its conclusions. Authors, for example, talk about “accuracy” and “errors” of the BeiDou navigation system although in practice they have evaluated its “uncertainties”. No one knows what the absolute and true coordinates of a site to give us reasoning to statements about "errors" of the system.
Again the problem with outliers has been obfuscated in this manuscript. No one knows what percentage of outliers exists in this analysis if these outliers have been deleted and not examined futher. If one has to get an appreciation of the BeiDou navigation system and its true capacities and strengths all results have to be presented (and not to delete values above 30 m as the authors stated). It would have been better if a boxplot diagram could have been presented so we all understand the BeiDou navigation system.
The English language of this manuscript contains lots of structural and grammatical mistakes. Some sentences of this manuscript do not make sense. For example, ‘besides” is not used correctly, titles of Tables are not making sense, and so on. The “satellite clock” cannot be defined but is performance and/or its parameters could be defined. Sometimes, uppercase letters are used for words.
The authors should give this manuscript to an English speaking person to correct the language and the way it is presented in this manuscript. This has not been done in this revision.
Comments made for station LHA1 are not true (Section 4.1, within -5 to 10 m???).
There are great discrepancies (improvement factors) in Fig.8 between station BRCH and all the rest. No justification is provided in the manuscript for such a deviation.
Maps of Position Dilution of Precision (PDOP) of the DeiDou navigation system are presented in the manuscript but these are not connected and related with the results presented. This is missing from the manuscript. The reader cannot understand why PDOP maps are presented in the manuscript.
The strange and systematic patterns of the results in Fig. 11 (as well as in other Figs, such as Fig. 20 for example) are not justified and or explained. Also why values are missing from these diagrams is not explained in the manuscript.
Author Response
Please see the attachment.Author Response File: Author Response.docx
