Prediction of BeiDou Satellite Orbit Maneuvers to Improve the Reliability of Real-Time Navigation Products

Round 1

Reviewer 1 Report

The article presents interesting research and very well prepared. Test procedure is clear and justified. Study data are rightly chosen and sufficient. The authors of the article correctly described the study; it is important that the test procedure can be reproduced by other researchers. Text is written in a logical and thoughtful way, creating a coherent whole, in accordance with the writing regime of scientific paper (IMRaD). The method of presentation, comprehensive introduction and very interesting and thoughtful practical examples deserve praise. Authors did a very good job - the text reads very well, and I have no comments.

Author Response

Dear reviewer: Thanks a lot for your comments. We appreciate your patience for this paper. And your comments give us a lot of encouragements. Best regards. Yours sincerely, Zhiwei Qin, Le Wang, Guanwen Huang, Qin Zhang, Xingyuan Yan, Shichao Xie, Haonan She, Fan Yue, Xiaolei Wang Chang’an University China

Reviewer 2 Report

Congratulations on the enhancement of the manuscript. You have applied the different comments of the reviewers and the manuscript is currently good. I do not have additional comments to the content of the manuscript, just review the English grammar to clarify some sentences.

Author Response

Dear reviewer: Thanks a lot for your comments. We appreciate your patience for this paper. And your comments give us a lot of encouragements. Best regards. Yours sincerely, Zhiwei Qin, Le Wang, Guanwen Huang, Qin Zhang, Xingyuan Yan, Shichao Xie, Haonan She, Fan Yue, Xiaolei Wang Chang’an University China

Reviewer 3 Report

As described in Section 1, GNSS satellites broadcast health flag indicating if users can use the satellite or not; The satellite will be set as unhealthy during maneuvers. In order to show the usefulness of the method proposed by this manuscript, it is necessary to explain and demonstrate the advantage of using maneuver prediction proposed by this manuscript instead of health flag broadcast by the satellite itself. In general, using health flag is enough to exclude maneuvering satellites and maintain position accuracy.

It is not clear how to use the orbit maneuver prediction factor P. In other words, the criteria to exclude satellites with predicted maneuvers is not clear. Describe relationship between the value of prediction factor P and satellite exclusion.

The difference of scheme 1 and scheme 2 is just the usage of C07 satellite. This means the difference of scheme 1 and scheme 2 is fixed and the method proposed as Eq. (8) is not applied. This means that Figures 8 to 14 do not support the method proposed in this manuscript. In order to support the conclusion, this manuscript must present the results with satellite exclusion based on Eq. (8).

Author Response

Dear reviewer: Thanks a lot for your comments. The manuscript (remotesensing-1099905) had been corrected following comments of reviewers and editor in this revision. We hope to fulfill the requests to your utmost satisfaction. We look forward to your response. Best regards. Yours sincerely, Zhiwei Qin, Le Wang, Guanwen Huang, Qin Zhang, Xingyuan Yan, Shichao Xie, Haonan She, Fan Yue, Xiaolei Wang Chang’an University China

Author Response File: Author Response.pdf

Reviewer 4 Report

This is a report on the remotesensing-1099905 manuscript submission entitled "Prediction of Beidou satellite orbit maneuvers to improve the reliability of real-time navigation products".

This reviewer finds the article an interesting prediction excercise. However, from a service point of view if this really happens and the satellite is not removed from the operational service, it is a major failure. I think such occurrences are very unlikely. On top of that, at the user level various anomaly and fault detection algorithms should be applied in order to detect and remove any faulty satellite or satellite measurement. Therefore, it is rather ambiguous what benefit the propose method brings to real-time operations. The problem they present a solution seems rather not to exist.

Other comments:
It is rather confusing why the authors joggle between C01 and C07 satellites. Some results refer to one satellite (GEO), some refer to other satellite (IGSO).

The paragraph dedicated to Figure 1 includes a sentence referring to purple line. There is no such color in the figure.

Very challenging to find what are scheme 1 & 2, and how do they differ. Their explanation is burried in the text. Perhaps a descriptive table will make things much more easier for any potential reader.

For some paragraphs (e.g., page 5,6,7) the text format use center alignment. This is different from the other paragraphs. Please adjust as appropriate.

Figure 4 shows indeed one can do a linear fitting for a short period of time. However, the linear fitting exhibits different slope and intercept. Is this unclear if this is a potential challenge for the method. In addition, does it mean that C01 experience a maneuver event every month or so?
If yes, it is very hard to believe that such events are not well documented and are not marked in the navigation data and transmitted to the users. Again, it is a matter of service reliability.

On page 16 some time stamps are perhaps incorrect: 07:00:00? 7:15:30?

Of course including a faulty satellite in the positioning solution leads to results such shown in Figure 14.

Figure 15, the graph on the left shows .... The graph on the shows ... Perhaps one word is missing in the latter. In addition, again the time stamp issue occurs in the last sentence of the paragraph.

The manuscript includes no Discussion section, where the authors should put their results into perspective with respect to other research and/or existing methodologies. Please consult the Instructions of Authors section for more details on manuscript structure.

Although there are several typos (such as verity, pg.3), the manuscript is written in good English. However, the sentence structure was found cumbersome at times. Therefore, the text has flown slowly. Some results could have been summarized in tables to increase reader experience.

 

Author Response

Dear reviewer: Thanks a lot for your comments. The manuscript (remotesensing-1099905) had been corrected following comments of reviewers and editor in this revision. We hope to fulfill the requests to your utmost satisfaction. We look forward to your response. Best regards. Yours sincerely, Zhiwei Qin, Le Wang, Guanwen Huang, Qin Zhang, Xingyuan Yan, Shichao Xie, Haonan She, Fan Yue, Xiaolei Wang Chang’an University China

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

I suggested users had the health flag and thus usefulness of this paper was not clear in Section 1. Now you mention you are using rapid precise orbit based on prediction, so it can be understood to predict the manuever. Ok.

I also suggested the difference of scheme 1 and scheme 2 was just the usage of C07 satellite and the method proposed as Eq. (8) was not applied. Now you mention removal of C07 is based on prediction information. Ok, they work well.

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

The article presents interesting research and very well prepared. Test procedure is clear and justified. Study data are rightly chosen and sufficient. The authors of the article correctly described the study; it is important that the test procedure can be reproduced by other researchers. Text is written in a logical and thoughtful way, creating a coherent whole, in accordance with the writing regime of scientific paper (IMRaD). The method of presentation, comprehensive introduction and very interesting and thoughtful practical examples deserve praise. Authors did a very good job - the text reads very well, and I have no comments.

However in terms of the editing there is some issues, e.g. formulas & figures formatting, but this is the editorial part so I leave it as a journal issue.

 

Reviewer 2 Report

I would like to congratulate you on this manuscript, it presents an interesting prediction approach based on collected data for Beidou satellite maneuvers. It is interesting how you applied the formulation to raise "warning" events that notify near orbit maneuvers. I would like, however, to forward you some comments that may enhance your manuscript:

1- Figure 1 seems that it does not contribute properly to the explanation. Considering that the figure is quite vague, I suggest to remove it and the corresponding explanation. In this way, I think that it is more productive to attach some references when you present the different perturbations (lines 104-106), rather than the proposed figure.

2- Figure 2 presents the differences between orbits due to external perturbations. Although "a" parameter is considered as semi-major axis, it seems that it does not follow the proper definition (while "b" parameter is correct). Could you clarify why do you defined this semi-major axis different as the common one for orbits?

3- Additionally, in lines 150-151 you indicate the difference between semi-major axes is represented in the figure, although it seems not. Please, solve this issue.

4- The definition of the prediction factor P (Definition 4 of Page 5) seems not accurate enough. Specifically, for all the cases the definition is exactly de same, while you should include some "otherwise" condition. Furthermore, may it be interesting to consider in the definition of the iterative process of P value with some index.

5- Figures 5 and 6 have the same caption, which may be difficult to understand the context.

6- In the same figures, it is possible to see that P value increases, and sometimes decreases. It is quite confusing for me this decrease process when its definition (Definition 4) always considers the increase case for specific conditions (P = P +1). Could you clarify the definition and this behavior? It seems that the P value can be 0, 1, 2, and 3 depending on the three conditions. If one of the conditions is true, then the P value is increased by one, but not iteratively over time. I suggest to clarify this definition properly

Reviewer 3 Report

In general, orbit maneuvers of a navigation satellite are announced to users in advance because they would affect the service. The BDS satellite transmits navigation messages including satellite health flag being unhealthy status before maneuver. The performance standards of Beidou also specifies that the notice of the scheduled outage is announced 24 hours before the outage. Thus, users have information of, at least, scheduled outages. This manuscript describes nothing about this fact; The usefulness of the method proposed by this manuscript is not clear at all. In Eq. (4), a_TF and t_TF essentially refers the same event because t_w is the predicted time that the semi-major axis exceeds a_w. According to Figure 6, a_TF contains some noise due to short-term perturbations; This suggests it is enough to employ t_TF and a_TF is not functional. Moreover, H_TF refers the health flag in navigation message which directly indicates the status of the satellite including maneuvers. Users have the health flag and do not need to predict the maneuvers. It is not clear how to use the orbit maneuver prediction factor P. What should users do if the attention level is not zero regarding the orbit maneuver prediction factor P? It is explained that when the orbit maneuver prediction factor P is 3, the satellite would be maneuvered in 1-2 hours later. However, Figure 8 shows the maneuver was conducted 10-15 minutes after 19:00:00 on August 23, 2019 with the health flag activated at 19:00:00. The difference of Scheme 1 and 2 seems the usage of C07 satellite, according to Figure 8 and related text; The difference of Scheme 1 and 2 is fixed and the method proposed as Eq. (4) is not applied. This means that Figures 8 to 14 do not support the method proposed in this manuscript.

Reviewer 4 Report

This is a report on the remotesensing-1041181 manuscript submission entitled "Prediction of Beidou satellites orbit maneuvers for improving the reliability of real-time navigation products".

At this point in time, the manuscript requires major review and significant language improvement. Unfortunately, it has been very challenging to comprehend numerous sentences and thus the content itself. They are numerous long and heavy formulated sentences (e.g., 3+ row sentences), incorrect verb tense usage (e.g., l378-388), rather unusual word choices (e.g., secrecy issues, abnormities, etc.) Only after a comprehensive language improvement, a proper review process becomes possible.

Nevertheless, this reviewer would like to point several things that the authors might consider for an updated version if any:

C01 (Figure 3) is a GEO, C07 (Figure 4) is an IGSO. Thus, the satellites behave differently. What is the purpose of presenting Figure 3 initially? Any particular reason why focusing on C07? There are numerous (10+) IGSO in total out there at the moment.

Linear trend over one month or few months in 2019 might be deceptive for drawing general conclusions. The authors should show visuals depicting the entire period interval that is mentioned (Feb 2013 to March 2019). Only after that, more solid inferences become possible.

Remove full stop from Figure. X both in the caption and when referring in the text. Use it only if abbreviation is used, i.e. Fig. X.

Rather ambiguous what are Scheme 1 and 2 and how they differ. The presence of the satellite in the precise products is not surprising, as long as the data transmission was not interrupted. Therefore, estimation of its position in space and clock bias is possible. However, the real time users must take into account the transmitted flags and discard such satellite from the positioning estimation accordingly, as the navigation data are marked invalid.

Easting/Northing, east/north, E/N all refer to same thing. Pick one and be consistent.

Figure 13 caption includes a typo.

It is rather ambiguous in the end what is the prediction method proposed in this manuscript, and how this prediction method really differs from the detection method reported by authors in Ref 19-21.