Expanding Imaging of Satellites in Space (IoSiS): A Feasibility Study on the 3-Dimensional Imaging of Satellites Using Interferometry and Tomography
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript extends the formerly published simulation aspects to real ground-based experiments using a single spatiality separated receiver. Experimental results promise a high-resolution imaging method for the future development for IoSiS. I think this manuscript merits the publication in this journal. Detailed comments are presented below.
(1) The differences between this manuscript and the formerly published papers should be claimed clearly.
(2) In the real observation scenarios, the range between the radar and the space target is changing with time. Will the translational motion compensation error influence the 3-D imaging quality?
(3) In the tomography-based imaging process, should the attitude of the space target be a prior information? Can be proposed method be applied when a non-cooperative space target is observed?
Author Response
Dear Reviewer,
I am grateful for your valuable feedback. I thank you for your time invested into the review.
In our revised manuscript, I have indicated all the changes I have made based on your comments with red highlighting. Similarly, I have included the number of new references I have added based on your review in red.
Please see my comments to your detailed feedback below.
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(1) The differences between this manuscript and the formerly published papers should be claimed clearly.
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I agree, we could have made it more clear. You can see the modified paragraph in line 39 to 48.
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(2) In the real observation scenarios, the range between the radar and the space target is changing with time. Will the translational motion compensation error influence the 3-D imaging quality?
(3) In the tomography-based imaging process, should the attitude of the space target be a prior information? Can be proposed method be applied when a non-cooperative space target is observed?
I will respond to both of those questions together. I agree that you bring up very important points which I should not have omitted. The main reason, why I didn't mention the translational motion compensation or the somewhat unknown attitude of the object, is that IoSiS is focusing on operational satellite. Operational satellites usually have a very well maintained attitude control, which allows a a-priori calculation of the expected motion, with only the knowledge about the orbital parameters. When imaging defective Satellites or space debris, the attitude must be estimated based using complex algorithms. But this holds true regardless of regular ISAR imaging or tomographic ISAR imaging. To further clarify this, the paragraphs from Line 67-76 and Line 162-165.
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Once again, I would like to thank you for your valuable feedback. I hope the revised manuscript is satisfactory to your standards.
Sincerely,
The Authors
Reviewer 2 Report
Comments and Suggestions for AuthorsMy understanding is that the paper proposed an initial technology involved interferometry and tomography to achieve 3-dimensional imaging for IoSiS. It would be better to consider revising the title and structure of the manuscript as they make readers feel confused now. For example, the structure can follow the traditional one with Introduction, Method, Experiment Setup, Experiment Results, Discussion, and Conclusion.
The English can be improved. It would be better to include paragraph cohesion statements to enhance the flow and readability of the manuscript.
1. Abstract: It would be better to add the comparative results of interferometry and tomography and their advantages and disadvantages.
2. Introduction: It would be better if the authors can enrich this part, such as providing a detailed description of other methods to achieve 3D imaging, their advantages and disadvantages, and the advantages of your proposed method.
3. Line 26: It would be better to give the full name of ‘RX’ when it is first mentioned. The same applies to abbreviations like ‘FPGA’ and ‘SSD’ and so on.
4. Line 89: It would be better to detail how this filter is set up and explain how it affects the result.
5. Line 90: It would be better to add an example to illustrate the layover effect.
6. Line 222 and 229: It would be better to add the reasoning behind the choice of base lengths.
7. Line 225: It would be better to discuss the effect of side lobes quantitatively and provide the results obtained using side lobe suppression techniques.
8. Line 235: It would be better to describe the material and surface reflection characteristics of the mock-up satellite in detail, clarifying its similarity to a real satellite.
9. Figure 10(b) and 11(a): It would be better to add annotations to highlight important areas to help readers understand the figures.
10. Figure 12: It would be better to add some quantitative indicators, such as resolution and error size, to show the accuracy differences between interferometry and tomography.
11. Future plan: It would be better to include a detailed future hardware expansion plan in the manuscript, such as the number of receivers to be added and the technical challenges anticipated.
Comments on the Quality of English LanguageThe English can be improved. It would be better to include paragraph cohesion statements to enhance the flow and readability of the manuscript.
Author Response
Dear Reviewer,
I am grateful for your valuable feedback. In our revised manuscript, I have indicated all the changes I have made based on your comments with green highlighting. Similarly, I have included the number of new references I have added based on your review in green.
Please see my comments to your detailed feedback below.
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My understanding is that the paper proposed an initial technology involved interferometry and tomography to achieve 3-dimensional imaging for IoSiS. It would be better to consider revising the title and structure of the manuscript as they make readers feel confused now. For example, the structure can follow the traditional one with Introduction, Method, Experiment Setup, Experiment Results, Discussion, and Conclusion.
Thank you for bringing this up to our attention, it is very valuable to see how the paper structure is observed. We have updated the Title to
"Expanding IoSiS: A feasibility study on 3-dimensional imaging of satellites using interferometry and tomography"
to clarify that this is directly investigating the SAR concept of Interferometry and Tomography.
Furthermore, a small paragraph was added to guide the reader along the structure of the paper (Line 49 to line 55).
In my understanding, our outline does not significantly differ from the traditional one, with the exception of the Section headings. I can see that this may cause confusion, which is why they have been updated, Line 56,221)
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The English can be improved. It would be better to include paragraph cohesion statements to enhance the flow and readability of the manuscript.
We regret to learn that our proficiency in English does not meet your expectations. Nevertheless, we concur that the flow of the text could be enhanced. Upon your kind request, we have added paragraph cohesion statements to enhance the flow and readability. Please see the revised text in the following line segments:
87-88
111-112
116-118
124-129
149-155
258-259
265-268
295-297
326-328
380-383
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1. Abstract: It would be better to add the comparative results of interferometry and tomography and their advantages and disadvantages.
I agree that the abstract needed a more comprehensive summary of the paper. It has been updated in accordance with your suggestion (Lines 1-13).
Abstract: As the need for new and advanced space situational awareness systems increases, new technologies for in-situ observations are needed. The experimental IoSiS (Imaging of Satellites in Space) system at the German Aerospace Center (DLR) is already capable of high-resolution imaging 3
tasks using inverse synthetic aperture radar technology. As 2-dimensional radar images can be difficult to interpret, full 3-dimensional imaging is desired. This paper extends the previously published simulation aspects to real ground-based experiments using a single spatially separated receiver, allowing interferometric measurements. However, as interferometry cannot fully resolve a 3-dimensional object, more spatially separated receivers are also considered for the use of ISAR tomography to gain experimental insight into true 3-dimensional imaging as IoSiS will eventually move towards a tomographic acquisition mode. The results shown here promise a high resolution imaging method for the future development for IoSiS. Based on the research presented here, additional receivers can be implemented into IoSiS to establish real world 3-dimensional measurements of space objects.
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2. Introduction: It would be better if the authors can enrich this part, such as providing a detailed description of other methods to achieve 3D imaging, their advantages and disadvantages, and the advantages of your proposed method.
Thank you for your valuable comment. I have mostly rewritten the introduction, I hope it is satisfactory to you.
However, I would like to mention, that this work focuses on the extension of the IoSiS Radar system, a comparison for 3-dimensional imaging outside a multistatic ISAR system (like an optical system for example) is in my opinion outside the scope of the submitted work, which is also why we revised the title. The updated Introduction can be found in Line 23 to 55.
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4. Line 26: It would be better to give the full name of ‘RX’ when it is first mentioned. The same applies to abbreviations like ‘FPGA’ and ‘SSD’ and so on.
We apologize for the oversight, this is a valuable and important point. We have made the corrections in the revised version. See the changes in Lines:
33, 226, 240,244,245, 433
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6. Line 89: It would be better to detail how this filter is set up and explain how it affects the result.
I am grateful for your feedback. I agree, the definition has been missing and has been added. I have changed the wording from "filter" to "mask" to clarify this. However, I would like to clarify that this does not affect the result per say. It makes the interferogram much easier to interpret with the human eye, as it is a mask, that is applied in the shown interferograms. Please read the updated paragraph, if it is now clear to you. Lines 120-124, 307-308,
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8. Line 90: It would be better to add an example to illustrate the layover effect.
Thank you for your feedback, I can see how the explanatory figure is not sufficient. I have added a simulation result to hopefully illustrate this. I hope the revised version is satisfactory. Lines 136-143 and Figure 3.
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9. Line 222 and 229: It would be better to add the reasoning behind the choice of base lengths.
Thank you for pointing that out. That has been an oversight from our part and has been updated on Lines 274-276 and 288-289).
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11. Line 225: It would be better to discuss the effect of side lobes quantitatively and provide the results obtained using side lobe suppression techniques.
I agree the effect was not discussed in detail. I have added more quantitative measurements as well as a more detailed description about the technique in the section Lines 280-286 and Table 1.
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12. Line 235: It would be better to describe the material and surface reflection characteristics of the mock-up satellite in detail, clarifying its similarity to a real satellite.
Thank you for your comment. I can see how this may be of interest to the reader . I have amended the description in the Lines 296-304. However, I would like to mention that this is a mock-up model to show the imaging principle. We do not expect special interactions with the radar signal and the satellite thus we modeled the features as to how we see them in out IoSiS images. As we do not have a CAD model of the test target, quantitative evaluation is challenging.
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14. Figure 10(b) and 11(a): It would be better to add annotations to highlight important areas to help readers understand the figures.
Thank you for this valuable point. The figures have been updated accordingly, they are now Figure 11(a) and 12(a).
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16. Figure 12: It would be better to add some quantitative indicators, such as resolution and error size, to show the accuracy differences between interferometry and tomography.
This is a good point, thank you for your feedback. However, I am not sure, I understand what you are expecting. There is no CAD model of the mock-up satellite we could compare our measurements to. The measurements were done qualitatively to show the expected image products from interferometric and tomographic measurement results. Especially, how the interferometric and tomographic measurements should be fairly compared with quantitative measures is unclear to me. The resolution (if you want to call it that way) in z-direction for interferometry is defined with the phase accuracy. But as I have shown with the experiment with the side lobe suppression, this phase is very sensitive to a lot of interference from the object itself, especially as interferometry cannot solve multiple targets along the z direction, rendering it challenging to quantitatively describe the 3-dimensional object.
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17. Future plan: It would be better to include a detailed future hardware expansion plan in the manuscript, such as the number of receivers to be added and the technical challenges anticipated.
Thank you for pointing that out. We did not go into exhaustive detail as this is still subject to change and a highly flexible topic. However, what I can confidently add, i have added to the summary in the lines 408-419.
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Once again, I would like to thank you for your valuable feedback. I hope the revised manuscript is satisfactory to your standards.
Sincerely,
The Authors
