Simulation Analysis of the Geometric Positioning Accuracy for MEO- and HEO-SAR Satellites

Round 1

Reviewer 1 Report (Previous Reviewer 4)

Paper by Zhao et al. is a resubmitted manuscript. As far as I can see, the authors have corrected the shortcomings noticed in the previous process of reviewing this paper. However, small shortcomings should be corrected.

I see that the authors have improved the abstract, but I think that it can be further worked on and shortened even more to make it clearer. The abstract must state the overarching goal or main objective(s) as well as the purpose/rationale of the study in two or three sentences …

Line 35:  Obvious missing Ref  1 and 2 “… [Error! Reference source not found.-2].” Please correct.

While the authors have improved the quality of the figures, they should invest a little more effort and at least increase the text on the axes of figures 11 and 12  as well as the titles of the axes of most of the figures.

Although the literature is appropriate, perhaps it should be expanded a bit regarding the discussion.

Author Response

General Comments:

1.Paper by Zhao et al. is a resubmitted manuscript. As far as I can see, the authors have corrected the shortcomings noticed in the previous process of reviewing this paper. However, small shortcomings should be corrected.

I see that the authors have improved the abstract, but I think that it can be further worked on and shortened even more to make it clearer. The abstract must state the overarching goal or main objective(s) as well as the purpose/rationale of the study in two or three sentences …

Response: Thank you very much for this comment. Thank you very much for the recognition of our work. We have carefully considered each comment and made our best efforts to carefully revise them. If there are areas where the understanding is not accurate or the modifications are not comprehensive, we hope that experts will give us another opportunity to make modifications. We must revise the manuscript until it meets the satisfaction of the experts. The result of the modification is as follows:

Due to the long synthetic aperture time, the large squint angle, and the large imaging width of Medium Earth Orbit (MEO) and High Earth Orbit (HEO) SAR satellites, it is difficult to simulate the geometric positioning accuracy of MEO and HEO SAR satellites through the SAR image simulation methods. In this paper, one non-zero Doppler simulation method of geometric positioning accuracy was proposed without simulating SAR images. In order to simulate the geometric positioning accuracy under different errors and imaging observation conditions, the virtual simulation geometric model was constructed by the simulated satellite ephemeris and the coordinates of ground control points (GCPs). On this basis, one geometric accuracy simulation method based on mean value compensation was proposed to simulate the geometric positioning accuracy with GCPs. The experimental results showed that the impact of Doppler center frequency error and velocity error of MEO and HEO SAR satellites on geometric positioning accuracy is significant compared with the LEO SAR satellites, and the maximum error they affect can reach about 1597 meter. In addition, the geometric positioning accuracies of MEO and HEO SAR satellites with GCPs can be achieved to 1~10 m and 7~29 m, respectively.

 

Specific Comments:

1.Line 35:  Obvious missing Ref  1 and 2 “… [Error! Reference source not found.-2].” Please correct.

Response: Thank you very much for this comment. We quite agree with you on this point. We rechecked all references for citations. We apologize for the bad reading experience.

 

2.While the authors have improved the quality of the figures, they should invest a little more effort and at least increase the text on the axes of figures 11 and 12 as well as the titles of the axes of most of the figures.

Response: Thank you very much for this comment. We quite agree with you on this point. We apologize for the bad reading experience. We have modified Figure 8-12. If there are areas where the understanding is not accurate or the modifications are not comprehensive, we hope that experts will give us another opportunity to make modifications.

 

3.Although the literature is appropriate, perhaps it should be expanded a bit regarding the discussion.

Response: Thank you very much for this comment. We quite agree with you on this point. We have rewritten the introduction to highlight something really new about our report and what is different from other reports. Other research is based on the SAR image and imaging mode of LEO-SAR satellites is orthogonal side-looking, that is, the Doppler center frequency is generally zero. However, the simulation of MEO- and HEO-SAR satellite images is laborious and inefficient. the synthetic aperture time of MEO- and HEO-SAR satellites are long, which not only generates a squint angle at the moment of imaging, but also makes it difficult to simulate images. Consequently, the simulation method adopted for LEO-SAR satellites is not suitable for MEO- and HEO-SAR satellites. If there are areas where the understanding is not accurate or the modifications are not comprehensive, we hope that experts will give us another opportunity to make modifications. We must revise the manuscript until it meets the satisfaction of the experts.

Reviewer 2 Report (Previous Reviewer 3)

I am satisfied with the changes performed to the manuscript and the responses to my questions. Congratulations on your work.

Author Response

I am satisfied with the changes performed to the manuscript and the responses to my questions. Congratulations on your work.

Response: Thank you very much for this comment. Thank you very much for the recognition of our work.

Reviewer 3 Report (Previous Reviewer 2)

the abstract is too long and scattered. I appreciate you better summarising the issue and writing in concise sentences what has been done and mentioning the experimental results.

There are errors in the references. The entire Introduction should be revised.

The formulae are scattered, there is a lack of section notation, there is a lack of punctuation, you do not understand anything about the domain. Then they all need to be revised a little, there are errors.

The table is all uncoordinated.

In the end, the article was constructed after doing some simulations on STK, it should be completely revised by highlighting more clearly what was discovered, with respect to the results that already exist within the state of the art.

From my point of view, this article cannot be accepted under these conditions.

The abstract has to be editated by a native English speeking person.

Author Response

General Comments:

1.the abstract is too long and scattered. I appreciate you better summarising the issue and writing in concise sentences what has been done and mentioning the experimental results.

Response: Thank you very much for this comment. Thank you very much for the recognition of our work. We have carefully considered each comment and made our best efforts to carefully revise them. If there are areas where the understanding is not accurate or the modifications are not comprehensive, we hope that experts will give us another opportunity to make modifications. We must revise the manuscript until it meets the satisfaction of the experts. The result of the modification is as follows:

Due to the long synthetic aperture time, the large squint angle, and the large imaging width of Medium Earth Orbit (MEO) and High Earth Orbit (HEO) SAR satellites, it is difficult to simulate the geometric positioning accuracy of MEO and HEO SAR satellites through the SAR image simulation methods. In this paper, one non-zero Doppler simulation method of geometric positioning accuracy was proposed without simulating SAR images. In order to simulate the geometric positioning accuracy under different errors and imaging observation conditions, the virtual simulation geometric model was constructed by the simulated satellite ephemeris and the coordinates of ground control points (GCPs). On this basis, one geometric accuracy simulation method based on mean value compensation was proposed to simulate the geometric positioning accuracy with GCPs. The experimental results showed that the impact of Doppler center frequency error and velocity error of MEO and HEO SAR satellites on geometric positioning accuracy is significant compared with the LEO SAR satellites, and the maximum error they affect can reach about 1597 meter. In addition, the geometric positioning accuracies of MEO and HEO SAR satellites with GCPs can be achieved to 1~10 m and 7~29 m, respectively.

 

 

Specific Comments:

1.There are errors in the references. The entire Introduction should be revised.

Response: Thank you very much for this comment. We quite agree with you on this point. We rechecked all references for citations. We apologize for the bad reading experience.

 

2.The formulae are scattered, there is a lack of section notation, there is a lack of punctuation, you do not understand anything about the domain. Then they all need to be revised a little, there are errors.

Response: Thank you very much for this comment. We quite agree with you on this point. We have rewritten the interpretation of Equations 1-4. We have re-updated the domain and corrected the citation errors in Reference 2. Looking forward to the expert's review again. If there are still any shortcomings, we will make further efforts to modify them.

 

3.The table is all uncoordinated.

Response: Thank you very much for this comment. We quite agree with you on this point. We have modified Table 1, Table 2 and Table 3. If there are any shortcomings, we sincerely hope that the reviewers can give us another opportunity to make corrections. Thank you again for your valuable comments.

 

4.In the end, the article was constructed after doing some simulations on STK, it should be completely revised by highlighting more clearly what was discovered, with respect to the results that already exist within the state of the art.

From my point of view, this article cannot be accepted under these conditions.

Response: Thank you very much for this comment. We quite agree with you on this point. We only use STK to simulate the orbit to obtain the position and velocity of the satellite. After that, a geometric model with no error parameters is constructed. Through analysis, errors are added to construct a geometric model. a non-zero Doppler simulation method of geometric positioning accuracy was proposed without simulating SAR images. Through experiments, we have found that satellite velocity and Doppler center frequency have a great influence on geometric positioning accuracy. Looking forward to the expert's review again. If there are still any shortcomings, we will make further efforts to modify them.

5.The abstract has to be editated by a native English speeking person.

Response: Thank you very much for this comment. We quite agree with you on this point. In this revision of the manuscript, time was rushed and we did not have time to polish it. However, we find experts with extensive review experience to revise manuscripts. We have tried our best to polish the language in the revised manuscript. And we hope the revised manuscript could be acceptable for you.

Reviewer 4 Report (Previous Reviewer 1)

The authors present interesting data about, a non-zero Doppler simulation method of geometric positioning accuracy was proposed without simulating SAR images. First, considering a series of geometric errors at the moment of imaging, a virtual simulation geometric model was constructed. Then, with the geographic coordinates of actual ground control points (GCPs), the real imaging geometric relationship was established to obtain the true values of virtual simulation geometric model parameters. The manuscript is well written and should be of great interest to the readers. However, the paper needs improvements before publication. More clearly results. All figures with charts could be bigger. Mention more about future work.

The authors present interesting data about, a non-zero Doppler simulation method of geometric positioning accuracy was proposed without simulating SAR images. First, considering a series of geometric errors at the moment of imaging, a virtual simulation geometric model was constructed. Then, with the geographic coordinates of actual ground control points (GCPs), the real imaging geometric relationship was established to obtain the true values of virtual simulation geometric model parameters. The manuscript is well-written and should be of great interest to the readers. However, the paper needs improvements before publication. More clear results. All figures with charts could be bigger. Mention more about future work.

Author Response

The authors present interesting data about, a non-zero Doppler simulation method of geometric positioning accuracy was proposed without simulating SAR images. First, considering a series of geometric errors at the moment of imaging, a virtual simulation geometric model was constructed. Then, with the geographic coordinates of actual ground control points (GCPs), the real imaging geometric relationship was established to obtain the true values of virtual simulation geometric model parameters. The manuscript is well-written and should be of great interest to the readers. However, the paper needs improvements before publication. More clear results. All figures with charts could be bigger. Mention more about future work.

Response: Thank you very much for this comment. Thank you very much for the recognition of our work. We quite agree with you on this point. We apologize for the bad reading experience. We have modified Figure 8-12. If there are areas where the understanding is not accurate or the modifications are not comprehensive, we hope that experts will give us another opportunity to make modifications.

In future work, the coupling characteristics of geometric positioning accuracy and geometric error of MEO-and HEO-SAR satellites can be studied through this method. This section is supplemented by the conclusion

Round 2

Reviewer 3 Report (Previous Reviewer 2)

Accepted

 

The English can be accettable.

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

This study implements a simulation method for the geometric positioning accuracy of MEO- and HEO-SAR satellites with and without GCPs. The positions and velocities of the MEO- and HEO-SAR satellites obtained from the RD positioning model were simulated using the STK software. The geographic coordinates of the actual GCPs in the simulated imaging area were combined to construct a virtual simulation geometric model of the GCPs and examine the error between the image point and the object point. The manuscript is clear, relevant to the field, presented well-structured, and scientifically sound. The manuscript’s results are reproducible based on the details given in the methods section. However, all figures with charts could be bigger because couldn’t be read.  Also, I think the paper needs in conclusion to mention more about their future work.  

Reviewer 2 Report

The abstract is too long and sometimes very confusing. separate the issue with the state of the art and then remove the state of the art from the abstract and insert it in the introduction (if not present). Try to keep a concise outline of the abstract similar to this:

The problem of is....

In this paper we..........

experimental results confirms.......

The article describes a radar imaging calibration method based on SAR acquisitions from MEO and HEO orbits. The idea sounds good. In contrast, the authors have to report on the energy degign of the satellites (link budjet) as a function of integration time. Then you should insert a section with a theme title and make a series of simulations should show the focused sync at different signal-to-noise ratios (e.g. 40 dB, 30 dB, 20 dB and 10 dB) indicating the required transmission power with fixed integration time and, with fixed number of scatterers (all existing targets within the observation footprint), also considering the quality of the SAR receivers currently on the market (thus their sensitivity in terms of minimum detectable power). If this is not done, which I consider to be a fundamental step that demonstrates its technological feasibility.

Thank you

Reviewer 3 Report

Dear authors,

I reviewed the paper entitled “Simulation analysis of the geometric positioning accuracy for MEO and HEO SAR satellites” by Ruishan Zhao et al.

In this paper, the authors propose a non-zero Doppler simulation method for the geometric positioning accuracy for Medium Earth Orbit (MEO) and High Earth Orbit (HEO) satellites without simulating SAR images. The first step is to construct a virtual simulation geometric model considering a series of geometric errors at the moment of imaging. To obtain the true model parameters, the real imaging geometric relationship is established using the geographic coordinates of actual ground control points (GCPs). The geometric positioning accuracy is finally evaluated under different error conditions.  Using GCPs and the simulated orbit parameters, the geometric positioning accuracies of MEO- and HEO-SAR satellites with different error conditions and with or without GCPs are analyzed. According to the results of the experiment, different variables influence the geometric positioning accuracies for MEO- and HEO-SAR satellites, rating their values to 1-10 m, and 7-29 m using GCPs.

The paper is well-conceived and the proposed method for analyzing the geometric positioning accuracy for MEO- and HEO-SAR satellites is novel. The paper is well-designed and written. The introduction provides enough background and bibliography to focus on the research problem. Finally, the objectives of the study are clearly defined. Please, briefly highlight the main conclusions (this is indicated in the instruction for authors). The methodology is well-exposed and easy to follow. The experiments are well-designed and clearly exposed and discussed. The conclusions should include the geometric positioning accuracies obtained in the study. They are indicated in the abstract.

The authors should have revised the pdf manuscript before submission because there is a problem when generating the markers for figures and tables. All the numbers of figures and tables must be revised along the manuscript.

Line 11 -> Replace “time” with “times” as the verb in the sentence is in the plural.

Lines 594 and 598. The reference should be with the number.

Figure 5 on page 11. Replace the figure with other that contains texts in English, not in Chinese.

Figure on pages 15-16. Add the texts below the subplots a, b, and c, in the caption of the figure.

Reviewer 4 Report

This study proposes a simulation method for the geometric positioning accuracy of  MEO- and HEO-SAR satellites with and without GCPs. Authors stated that the method proposed in this paper can provide requirements for the design and index demonstration of MEO- and HEO-SAR satellites. The presented work has its scientific significance. However, a few issues should be carefully addressed before acceptance.

The Abstract does not meet the standards of the Journal. The abstract should summarize concisely the content and conclusions of the article and should be written as one paragraph (300 words). Please correct.

Currently, the introduction has a huge paragraph (lines 47-77) that should be divided, and the goal of the research should be highlighted in one of them. The authors should highlight if they report something really new or something different than others reported.

Line 383: Authors stated “This indicates that the simulation method proposed in this study is effective.” Can the authors further elaborate this.

Figure 2. I can’t see text in Flowchart. Please correct i.e. enlarge the text. Also, the text on the axis should be enlarged in Figs. 8-12.

Maybe the table 1 should be designed better.

Line 639 sentence “(1) As determined by the method validation experiments, the method proposed in this paper is effective.” is general and should be more specific.

Author Contributions. The authors should use initials.

Although the literature is adequate it should be expanded. I mean above all the references related to shortcomings in Introduction.

In references: if you use abbreviation of journals than make uniform.