Performance Analysis of the Korean Positioning System Using Observation Simulation

Round 1

Reviewer 1 Report

The paper is very interesting.

For this particular research type, I find no justification for reporting RMS at tenths of millimetre. Please fix this issue.

 

Author Response

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Reviewer 2 Report

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Comments for author File: Comments.pdf

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Reviewer 3 Report

Review of the paper „Performance analysis of the Korean Positioning System using observation simulation” submitted to Remote Sensing.

The paper discusses the positioning quality based on the proposed, new, satellite constellation as an independent satellite positioning system and with a combination with GPS. The methodology employed is correct and the paper is well written with very few language issues. I recommend acceptance of the paper after a revision.

Specific issues

1. In Table 2, we can find that the ECOM model is employed for solar radiation pressure modeling. In Table 2, we also find that orbit normal mode will be employed for KPS GEO, whereas yaw steering, and orbit normal mode will be used for KPS IGSO. ECOM model, as well as the Extended ECOM2 model, are dedicated to the satellites only in yaw-steering mode. They do not provide proper results for satellites in normal orbit modes, such as QZSS or BDS. Due to a large number of orbit modeling issues, most of the future QZSS and BDS satellites will orbit only in the yaw-steering mode. This should also be considered for the new Korean satellite constellation. There is a special version of the ECOM model dedicated to normal steering mode (see https://doi.org/10.1016/j.asr.2019.07.031), but this model does not provide as good results as those for satellites in the yaw-steering mode.
2. All models from Table 2 should be supported by proper references.
3. Will the Korean Positioning System be supported by the Laser Retroreflector Arrays for Satellite Laser Ranging? Galileo, GLONASS, BDS, QZSS, NAVIC, and future GPS-III satellites are equipped with Laser Retroreflectors for the orbit validation, precise orbit determination using two independent techniques, co-location in space, geocenter determination, and realization of the SLR reference frames using the SLR-to-GNSS observations. It would be worthwhile having also the SLR technique onboard KPS.
4. Figure 3. In my opinion, the accuracy of the GEO satellite orbits is far too low. The radial accuracy which is measured directly by SLR for BDS GEO is 87 mm and for BDS IGSO, it is 51 mm for the combined IGS multi-GNSS orbits, see: https://doi.org/10.1007/s10291-020-0965-5 There are several issues related to precise orbit determination of GEO satellites that remain unsolved, e.g., the lack of the variations in observation geometry or the resonance with the rotation of the Earth. Hence, the accuracy of GEO orbits is much lower than the accuracy of MEO orbits. The quality of GEO orbits can be improved by LEO satellites, see: https://doi.org/10.1007/s10291-020-0962-8 however, the Korean Positioning System does not consider LEOs. Therefore, this issue should be addressed in the paper.

Author Response

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Reviewer 4 Report

The article entitled "Performance analysis of the Korean Positioning System using observation simulation" is generally well written. The manuscript has a good literature review. The presentation quality is poor. I suggest providing figures with proper font size and appropriate resolution. English quality is good with minor errors, eg. plural form needed in row 57. Native speaker check recommended. The authors provide no information on the progress or plans for launch schedule or on current SVs space missions (if there are any). In the description of the KPS orbital parameters an error was found. The authors used RAAN as AN nodes determinant parameter while it is restricted to the celestial systems with orientation to the Pisces’ First Point of Aries. Even most basic textbooks contain information of referencing the space segment to the Prime Meridian of Greeenwich and LAN parameter. Correction necessary to be introduced in the text. Map background should have information on projection used, Transverse Mercator I guess. Fig. 2 is unclear with very small font used. Do all 31 GPS SVs ground tracks are included in the figure? The authors use occasionally too general phrases, eg. ‘seem to be similar’ in row 235. Please give precise value to compare. Simulation from Fig. 5 is not time-tagged. What epoch of GPST or UTC does it represent? Again, in Fig. 7 there are only 24 GPS SVs’ PRNs. Where is the rest? Fig. 8 and 10 are hardly readable.  The research methodology is well defined but results section need improvement. Both experimental or theoretical methods are explained correctly. The overall merit is generally positive. I recommend acceptance for publication after major revision.

Author Response

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Reviewer 5 Report

Choi et al.'s article is interesting and deserves to be published, once clarifications will have been made to the manuscript, essentially at the end of it.

For the simulation, simplifying assumptions have been made (Table 2): 1/ elevation weights, white noise for clock errors. These assumptions must be clearly explained. What are the real structures of these noises? How can you replace these "true" noises by the necessary simplifications done for the simulation?

After line 237, section 4, the paper becomes difficult to read. Too many acronyms are used: KPS+GPS SPP, KPS-only etc...and the reviewer had to read again and again to understand what was exactly done. 

Many results are comparisons, but with respect to what? Please explain clearly what are the references for the comparisons.

I urge the authors: To make the captions of the Figures totally independent of the text. This is the policy for all scientific literature. For example Figure 9 is relative to the grids of Figure 8. Same for Figures 11 and 10. Make this clear in the captions and please describe in the captions the main conclusions of the Figures. Do not assume that the paper will be read in full, so the main results must be clearly identified. May be a list of acronyms will improve the readability.

The English of the conclusion must be also improved.

See also handwritten remark line 391.

I attach the manuscript annotated by hand, with all these points highlighted. 

 

 

 

Comments for author File: Comments.pdf

Author Response

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Round 2

Reviewer 4 Report

All necessary corrections were introduced. The paper is ready for publication.

Reviewer 5 Report

 

The authors took into account all the reviewers comments.

 

Manuscript is OK now.