Research on the Real-Time Ambiguity Resolution Algorithm of GPS/Galileo/BDS Based on CNES Real-Time Products

Round 1

Reviewer 1 Report

The novelty of this manuscript is not given clearly in the introduction. I can find a lot of publications which are all related to multi-constellation PPP-AR using products of CNES such as Liu et al.(2020), Du et al.(2022). It is not enough to introduce BDS into the data processing and evaluate the products again. The authors need to reorganize the introduction to show the sell point. 

Reference

Liu T, Jiang W, Laurichesse D, et al. Assessing GPS/Galileo real-time precise point positioning with ambiguity resolution based on phase biases from CNES[J]. Advances in Space Research, 2020, 66(4): 810-825.

Du S, Shu B, Xie W, et al. Evaluation of Real-time Precise Point Positioning with Ambiguity Resolution Based on Multi-GNSS OSB Products from CNES[J]. Remote Sensing, 2022, 14(19): 4970.

The language in the manuscript is difficult to understand. It is better to ask for the help from someone proficient in English.

Author Response

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Reviewer 2 Report

The study addresses a compelling question in real-time PPP-AR, and I appreciate the efforts made by the authors in conducting this research.

Minor Revisions Comments:

Section 3.4: “Figure 7 depicts the time series of the HOLB station in kinematic mode over 150 days in 2023, displaying RT PPP and RT PPPAR modes”

I believe this sentence is ambiguous. Based on my understanding, the figure displays the results of a single day, not 150 days. However, the description seems to imply continuous results over 150 days. Please confirm.

Figure 7 and 8:

It's better to use 'RT PPP' instead of 'RT' in the legend for clearer understanding. And normally we called "real-valued solution" as "float solution".

Table 1:

How to deal with ISB and earth tides? Please add.

Equation 23：

explain what is  λ_n.

Conclusion

This manuscript provides valuable insights into real-time PPP-AR using CNES products. The minor issues outlined above do not detract significantly from the quality of the work but addressing them would enhance the overall impact and clarity of the manuscript. I believe that with these minor revisions, the manuscript will be well-suited for publication in this Journal.

Despite some minor language issues, your paper generally maintains a coherent flow and is able to convey the main points effectively. The overall structure of the paper adheres to a logical sequence, which facilitates the reader's comprehension.

Author Response

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Reviewer 3 Report

This paper evaluates the real-time PPP ambiguity resolution performance with GPS/Galileo/BDS satellite systems using the real-time orbit, clock, and phase biases from the CNES analysis center. The wide-lane and narrow-lane ambiguity residuals after removing the phase biases are used to indicate the phase biases quality. The convergence time and positioning error of single-system and combined-system PPP are assessed. Generally, the paper is easy to follow. The structure is clear and the content length is proper.

However, the algorithm is neither new nor clearly presented. The algorithm in the paper has been well introduced in a lot of the existing studies. In addition, (1) how the CNES products especially the phase biases, (2) how to use the CNES phase biases, (3) the ambiguity resolution preprocessing, procedure, and validation, are not presented in detail. It makes the PPP-AR tests in this study cannot be easily reproduced.

Ten days of multi-GNSS data from 22 MGEX stations in 2023 are used for tests. Is the Kalman filter initialized every hour or other? If not, there are only 220 daily samples for PPP performance analysis. It is not enough to derive a convincing conclusion. Therefore, suggest redoing the tests with more GNSS data.

The BDS PPP processing method is not clearly introduced. Is BDS-2, BDS-3, or BDS-2+3 used? How to deal with the inter-system code bias between BDS-2 and BDS-3? Do the authors fix BDS-2, and BDS-3 ambiguities separately? These points are very important to the BDS PPP AR performance so the authors should add more descriptions.

Other minor comments:

1. [Introduction] “technique for mitigating the minor weekly deviation Fractional Cycle Biases (FCB).” Not clear.

2. [sec 3.1] “IGS snx files” what is snx file?

3. [table 1] Please check the Galileo observation frequency, E1/E5a? What is GF+MW cycle slip method?

4. Suggest to change the figure 8 style. There is too much information, and it is not easy to distinguish the different sub-figures.

Author Response

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Reviewer 4 Report

Dear Editor and Authors,

Thank you for giving me the opportunity to read the paper entitled: “Research on real-time ambiguity resolution algorithm of GPS/Galileo/BDS based on CNES real-time products”.

This paper focuses on GPS/Galileo/BDS PPPAR. The research is interesting and the work is solid. Some modifications should be made before publication.

1) The title of the paper needs to be revised, and it is not clear and specific, suggest adding PPPAR here.

2) The current research status does not provide a detailed introduction to real-time precise point positioning, and the author does not list the latest research progress.

3) There are many formulas, many of which are meaningless.

4) The experiment selects 22 reference stations, and it is recommended to choose representative stations.

5) The definition and use of a certain concept are not unique and confusing.

6) In the experimental section, experimental analysis with frequent repetitive language descriptions.

7) Result analysis should be elaborated in depth.

8) The conclusion section is not in-depth, and it is recommended to modify it.

9) The author needs to read the whole text very carefully again, which contains many grammar and spelling errors.

Author Response

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Round 2

Reviewer 1 Report

The authors have well polished  the innovations and languages of this study. Now I think it is appropriate to be published.

Author Response

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Reviewer 3 Report

The authors have well addressed the proposed issues and greatly improved the paper.

Please check the paper throughout and make sure the necessary part has been updated, for example, the used GNSS sites in the abstract.

Author Response

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