GNSS Real-Time ZTD/PWV Retrieval Based on PPP with Broadcast Ephemerides
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this paper, the authors have investigated the feasibility of utilizing GNSS precise point positioning (PPP) with broadcast ephemerides (BE-PPP) for retrieving zenith tropospheric delay (ZTD) and precipitable water vapor (PWV). The accuracy of real-time ZTD/PWV retrieval by the BE-PPP method are also assessed in this paper by processing GPS/Galileo observations taken from 80 IGS stations and 20 EPN stations during a 30-day experiment by applying both RT-PPP and BE-PPP solutions. However, several important technical and presentation related issues are found throughout the paper based on which the following suggestions are made to improve the contents of the paper.
1. The phrase ‘Error! Reference source not found’ appeared at multiple places within the text in the first paragraph of Introduction must be removed and reference number should be mentioned within a pair of third braces ([]).
2. The first sentence of Introduction should be backed up by appropriate reference.
3. The reason behind wide adoption of PPP approach to achieve accurate ZTD and PWV along with the relationship between the ZTD and PWV should be briefly discussed in 1st paragraph of Introduction to clarify the motivation of this research. Moreover, how the real-time ZTD affect PPP real-time atmospheric parameters retrieval operation should be more explained in the subsequent paragraphs to show the actual significance of using the former to carry out the latter.
4. In subsection 2.1, the framework of GPS/Galileo observation should be illustrated. The caption of table 1 should be changed since it describes mainly the characteristics of various items related to ZTD/PWV retrieval procedure using BE-PPP method rather than defining their processing strategies.
5. In subsection 2.2, the working methodology of BE-PPP algorithm should be described at first before describing GNSS ZTD/PWV retrieval based on BE-PPP procedure. Moreover, the workflow diagram of the proposed method should be provided.
Author Response
comments 1:The phrase ‘Error! Reference source not found’ appeared at multiple places within the text in the first paragraph of Introduction must be removed and reference number should be mentioned within a pair of third braces ([]).
responses 1:Modification completed.
comments 2:The first sentence of Introduction should be backed up by appropriate reference.
responses 2:Supported by references, cited.
comments 3:The reason behind wide adoption of PPP approach to achieve accurate ZTD and PWV along with the relationship between the ZTD and PWV should be briefly discussed in 1st paragraph of Introduction to clarify the motivation of this research. Moreover, how the real-time ZTD affect PPP real-time atmospheric parameters retrieval operation should be more explained in the subsequent paragraphs to show the actual significance of using the former to carry out the latter.
responses 3:The advantages of PPP technology in inverting ZTD and PWV have been briefly introduced. The content about the influence of ZTD on PWV inversion is introduced in Section 2.2.
comments 4:In subsection 2.1, the framework of GPS/Galileo observation should be illustrated. The caption of table 1 should be changed since it describes mainly the characteristics of various items related to ZTD/PWV retrieval procedure using BE-PPP method rather than defining their processing strategies.
responses 4:The reference frame of GPS broadcast ephemeris is WGS-84, and the reference frame of Galileo is GTRF; the title of Table 1 is modified to the implementation details of the BE-PPP program.
[11]GPS.GOV.Interface Control Documents: IS-GPS-200[DB/OL](2022-08-22)[2024-07-08].https://www.gps.gov/technical/icwg/IS-GPS-200N.pdf
[13]European GNSS Service Centre. Galileo-Open Service-Signal In-Space Interface Control Document (OS SIS ICD v2.1) [DB/OL].(2023-11)[2024-07-08]https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.1.pdf
comments 5:In subsection 2.2, the working methodology of BE-PPP algorithm should be described at first before describing GNSS ZTD/PWV retrieval based on BE-PPP procedure. Moreover, the workflow diagram of the proposed method should be provided.
responses 5:In Section 2.2, we first introduce the mathematical model of the BE-PPP algorithm, and then describe the basic theory of inverting GNSS ZTD/PWV using the ZWD estimated by this model. Based on your comments, we add a new section to describe the technical route of inverting ZTD/PWV based on BE-PPP, and the corresponding details.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have worked on "GNSS Real-Time ZTD/PWV Retrieval Based on PPP with 2 Broadcast Ephemerides". I have a few questions/suggestions prior to accepting it.
1. Some sentences in the manuscript have poor logicality and need to be improved.
2. Mention key findings of the study with a comparison to literature in the abstract one line.
3. The authors should consider rewriting the pertinent content in their manuscripts to emphasize the significance and value of their work more attractively and convincingly. Furthermore, presenting this information in a bulleted or listed format is recommended.
4. The research idea seems interesting, but the set goals are not achieved. What is the main significance of the paper in comparison with related published works?
5. To enhance the breadth and relevance of your work for a wider readership, I suggest including some recent references on GNSS Real-Time ZTD/PWV Retrieval in the manuscript. These references can provide additional insights and context to your research.
10.1109/ACCESS.2024.3350779
https://doi.org/10.1016/j.geog.2023.12.002
10.1109/ACCESS.2024.3353294
Author Response
comments 1:Some sentences in the manuscript have poor logicality and need to be improved.
response 1:The full text has been polished.
comments 2：Mention key findings of the study with a comparison to literature in the abstract one line.
response 2: Comparisons have been made with recent and similar studies.
comments 3:The authors should consider rewriting the pertinent content in their manuscripts to emphasize the significance and value of their work more attractively and convincingly. Furthermore, presenting this information in a bulleted or listed format is recommended.
response 3:Some of the introductions have been adjusted based on your suggestions.
comments 4：The research idea seems interesting, but the set goals are not achieved. What is the main significance of the paper in comparison with related published works?
response 4：This paper aims to propose a real-time inversion method of ZTD/PWV based on broadcast ephemeris PPP as an alternative to compensate for the shortcomings of real-time PPP affected by the network and intersatellite links.
comments 5:To enhance the breadth and relevance of your work for a wider readership, I suggest including some recent references on GNSS Real-Time ZTD/PWV Retrieval in the manuscript. These references can provide additional insights and context to your research.
response 5:A references you suggested has been added.
Reviewer 3 Report
Comments and Suggestions for AuthorsPPP is a positioning technique that removes or models GNSS system errors to provide a high level of position accuracy from a single receiver. A PPP solution depends on GNSS satellite clock and orbit corrections, generated from a network of global reference stations. Once the corrections are calculated, they are delivered to the end user via satellite or over the Internet. These corrections are used by the receiver, resulting in decimeter-level or better positioning with no base station required. Precise point positioning (PPP) stands out as an optimal approach for providing standalone static and kinematic geodetic point positioning solutions using all the available GNSS constellations. In this study, authors investigated the feasibility of utilizing BE-PPP for retrieving zenith tropospheric delay (ZTD) and perceptible water vapor (PWV). They reported that the real-time retrieval of ZTD/PWV using the BE-PPP solution is feasible and meets the accuracy requirements.
There are similar studies in the literature for different scientific fields on the subject. The following statements are made in the publication titled "Real-Time Precise Point Positioning Method Considering Broadcast Ephemeris Discontinuities", published by Cheng from the Shanghai Astronomical Observatory in 2024.
“BE-PPP with Galileo and the Global Positioning System (GPS) can provide a positioning accuracy of a few decimeters when post-processed products or real-time orbit and clock streams are not available (Carlin et al., 2021; Hadas et al., 2019). With the improved accuracy of the BDS-3 orbit and clock offset (Geng et al., 2022), BE-PPP for BDS has become feasible and offers better accuracy than standard point positioning (G. Chen et al., 2022), but lower accuracy than traditional PPP (Hadas et al., 2019).”
My suggestions to improve the quality of the publication are written below.
1. There are errors in the reference numbers of the manuscript.
2. The introduction part is insufficient in terms of literature.
3. Although the results are explained in detail, there is no comparative discussion with similar studies.
Comments on the Quality of English LanguageThere are major grammatical errors in the writing language.
Author Response
comments 1:There are errors in the reference numbers of the manuscript.
response 1: It has been modified.
comments 2：The introduction part is insufficient in terms of literature.
response 2：Corresponding supplements have been made.
comments 3：Although the results are explained in detail, there is no comparative discussion with similar studies.
response 3：Comparisons have been made with recent and similar studies.
Reviewer 4 Report
Comments and Suggestions for AuthorsDear Authors,
The manuscript explores the feasibility and accuracy of deriving zenith tropospheric delay (ZTD) and precipitable water vapor (PWV) using GNSS broadcast ephemerides (BE-PPP). In this study, both BE-PPP and RT-PPP methods were employed to compute and compare results based on data from 80 IGS and 20 EPN stations.
The paper introduces an innovative approach by utilizing GNSS broadcast ephemerides, underscoring its potential applications in atmospheric measurements. The methodological thoroughness and extensive data analysis conducted in the study reinforce the reliability and validity of the findings.
However, I think the manuscript could be strengthened with some minor corrections and additions. There are also some omissions and incorrect references in the text. Therefore, I kindly request that you thoroughly review the attached PDF and consider the feedback provided. Please make the necessary revisions accordingly. Addressing these points will significantly enhance the clarity and precision of your manuscript.
Best Regards,
Comments for author File: 
Comments.pdf
Author Response
comments 1：However, I think the manuscript could be strengthened with some minor corrections and additions. There are also some omissions and incorrect references in the text. Therefore, I kindly request that you thoroughly review the attached PDF and consider the feedback provided. Please make the necessary revisions accordingly. Addressing these points will significantly enhance the clarity and precision of your manuscript.
response 1：Thank you for reading my manuscript carefully. I have revised it carefully according to your comments.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAll my raised concerns are addressed in the revised manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsThank you for contributing to the scientific literature on the subject.
