Atmospheric Pre-Compensation of Ground-to-Space Communications with Adaptive Optics: Past, Present and Future—A Field Review
Round 1
Reviewer 1 Report
The authors presented a comprehensive review of the field of AO-based uplink pre-compensation. This manuscript has a reasonable structure and clear thinking. The authors discussed the future prospects of AO-based uplink pre-compensation and potential trade-offs between performance, cost, and operational considerations. This manuscript can be published after following revisions.
1. In Eq.1, what are the meanings of the parameters z and L.
2. Ref.12 is not cited in this manuscript.
3. On line 195, what are the meanings of the parameters D and L.
4. On line 266, what is the complete spelling of word “ALPHA-UP”.
Author Response
Please see attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper gives a substantial investigation of the past, present, and future of the ground-to-space communications system with adaptive optics under atmospheric pre-compensation. The considered topic is interesting and will provide guidance for the further investigation of adaptive optics. Nevertheless, the reviewer holds some concerns about this work which you can find below. I suggest that the authors revise and improve the manuscript accordingly.
The author provides a noticeable number of literature to find research gaps and motivation, which is not convincing. Highlight the research gap and main contribution of this article which is not addressed before.
“Adaptive Optics” in the abstract and the main bold of this work should be corrected to “adaptive optics”.
What’s the meaning of F(\cdot) in Eq. (1). In addition, the symbols used in the system modeling section are not well defined. It is advised to define all the symbols clearly to make the paper easy to understand,
Fig. 2 should be corrected since there are many Chinese and Japanese words.
AO is a significant work to compensate for the influence of atmospheric turbulence-induced wave fluctuations, and thus induce signal degradation. Without AO, the channel model can be modeled by many distributions, such as Gamma-Gamma (doi:10.3390/electronics9040646), lognormal (doi: 10.1109/TCOMM.2014.010914.130249), Malaga (doi: 10.1109/TVT.2023.3252822), etc. However, what will happen for the channel model when the AO technique is applied? I think more discussions about this will attract more readers to this paper.
Minor editing of English language required.
Author Response
Please see attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Please see the full review attached.
Comments for author File: Comments.pdf
Minor editing of English language required, overall, it is OK.
Author Response
Please see attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
The paper provides a review of past and current efforts at uplink precompensation for lasers for optical communication. Section 3 which has a review of the background math and benefits of precompensation is quite useful. The paper will also be useful for the various references. The discussion of the various efforts is more of a recitation of the projects and doesn't synergize. The author didn't compare and contrast or show how each project influenced the field. That's probably hard to do, but the best reviews aspire to do that.
One way the paper could be improved if the author had discussed future work that the field needs. What are the top 3 biggest concerns and avenues of research that are needed. From her readings, does the author have any insights?
For the many different systems, the author doesn't explain what communication protocols are being used. Coherent modulation schemes such as DPSK will have different requirements than PPM or OOK.
Figure 1. The Red and Orange lines are hard to distinguish. A more distinct color would have been a better choice. Green or Purple maybe.
Line 152 "Tyson’s analysis revealed that implementing a ground-based adaptive optics system with more than 50 actuators..."
is that 50 actuators across the pupil, or total? I assume the later, but it should be clarified. What size pupil was that computation for and for what wavelength?
line 160. It would be useful to say what country CRL/NICT is located in. I had to look it up. ie "In 1996, the CRL of Japan..."
Line 170 "The proposed system was a remarkable breakthrough at the time."
What aspects of the proposed design were a breakthrough? Much higher order AO systems had been developed by 1996 and even more by 2006. Did the system ever have any results in the lab? What impact did it have on future systems?
"While the focus of this publication..."
"This publication" implies it is the current article, rather than the reference. I think it should be "that publication"
The use of 2 DMs to correct phase & amplitude is going to be much more useful for horizontal path because of the deep turbulence and correspondingly higher Rytov numbers those systems encounter, rather than the higher elevation angles that are used for ground/space links. I am not sure it's actually that relevant to uplink scenarios (other than at very low angles.)
Line 230 "An experiment known as the Optical Feeder Link Adaptive Optics (OFELIA) was conducted by TNO and DLR ["
Acronmys should be spelled out and with organizations its often useful to list the country.
Figure 2. The figure should be redrawn to not include Japanese writing, as the rest of this paper is in English. Also, since the caption only explains a few elements in the drawing, it is hard/impossible to figure out what is going on in the figure. It needs additional explanation.
In general, I am not sure the diagrams of other systems are useful, as they are not discussed and nothing is really added by them. People interested in more details can read the references.
Line 290 "The CaNaPy system features a remarkable 70+ W 589 nm laser, currently unmatched in its capabilities."
Please provide more information. What are the unmatched capabilities? Why is it remarkable?
Line 294 Hart et al (2016) used a similar technique to do daytime Na LGS work.
https://ui.adsabs.harvard.edu/link_gateway/2016JATIS...2d0501H/doi:10.1117/1.JATIS.2.4.040501
Line 302 "ALASCA marks a significant milestone as a pioneering operational system at TRL6..."
An operational system would be TRL9, not 6. Demonstrations are TRL6
https://en.wikipedia.org/wiki/Technology_readiness_level
Line 359: 'For example, the maximum point-ahead angle for a communications link with Mars is 387 mrad [34], while the 360
corresponding point-ahead angle for near-Earth spacecraft is typically 20-50 mrad.'
The biggest problem is that 387 urad is larger than the isoplanatic patch size and measuring tip/tilt is an unsolved problem. The author seems to be ihinting that this is the problem,but doesn't come out and say it. Why not?
There are some awkward phrases and transitions. The author should have a colleague read over the paper and provide comments on the writing.
For example:
Line 52 "If optimal signal transmission wants to be ensured, Adaptive Optics (AO) pre-correction of the uplink signal might be required."
I think I know what this means, but the wording is awkward and I had to stop and try to figure it out.
Another example:
Line 158 "This emphasizes the significance of mitigating the effect of anisoplanatism by employing a beacon directed towards the uplink location beforehand."
This sentence was a bit confusing to me. Could it be rephrased?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
This manuscript cannot be accepted this time since not all my comments have been well solved. Such as comments #1, 3, and 4. In addition, the author's reply is arbitrary and I cannot get where the corrects have been made.
Moderate editing of the English language is required.
Author Response
Dear Reviewer,
I have addressed all your comments. Please have a look at the resubmitted version of the manuscript, once again. Apologies if my response was not clear enough. Thank you for taking the time.
Regards
#1 All Adaptive Optics instances are spelled this way to take into account that the term is usually referred as 'AO'.
#3 That schematic has been removed from the main manuscript.
#4 The channel modelling is a very large topic, which was not covered in this paper.
