Design of f-SCAN Acquisition Mode for Synthetic Aperture Radar

Round 1

Reviewer 1 Report

Dear authors,

My first general remark is that the quality and usefulness of the proposed technique (F-Scan) is very difficult to evaluate because in the article you have omitted many details. I'd like to ask the authors to improve the explanations.  

The comparison with SCORE (or in general DBF) does not seem fair, or at least not clear.  Authors devaluate SCORE with arguments that are either not true or do not have any evidence to support .

Usual DBF systems use Tx beam able to illuminate the swath of interest. So wide enough to avoid frequency dispersion. The Rx elements also have  wide beams. Rx elements with wide beams is a requirement otherwise DBF will not make sense.

Furthermore, the article in general is very difficult to understand. The structure and explanation needs to be improved. Is f-Scan applied per pulse? Is then apply on transmit or on receive?  Also, the comparison with SCORE (or DBF) is not clear. For example, in a SCORE system, how much the point direction of the beam will change for the example : Central frequency 9.8 GHz Available bandwidth 1.2 GHz. 

Specific comments:

page1.line2 "get high noise sensitivity". A system that is sensitive to noise? 

p1,ln33: What is MAPS? do you mean TOPS?

p2.ln50:"While SCORE requires DBF technology to have real-time receive beams changing with returning echo" Not necessary true. Otherwise what is the advantage of doing DBF over classic beamforming.

p2ln53"f-SCAN the same result is achieved by using only phase shifters and time delay lines on the phased array antenna" Design of delay lines and phase shifters for large bandwidths is not trivial

p2ln57"In transmission, the beam is scanned from far to near range. " why?

p2ln58"the other hand, the receiving pulse is shorter than expected by geometry, due to the directional filter operated by the RX beams" I can't really understand why this happens. Explanation needed.

p3 Figure1. It is not clear how much scanning there will be if no phase shifters are used and only a frequency sweep

p4 section 2.2 Design of phase shifters and delay lines in f-SCAN: what are the constrains? no grating lobes? narrow grating lobes? Please starts with the basics , Scan on Rx or Tx, 

p4 eq.6 where does this come from? eq 2. =2\pi gives a different result

p5 eq.9 : the initial requirement of a swath width (\delta \theta) is not used in the delay line calculation?

p5 eq 10 :Where does it come from, is it from sum(single element*exp(2\pi \psi)  and \psi in from eq 2

should Theta_emb be inside sum and be element dependent?

p5 lns131-136: I don't understand the discussion. Embedded pattern is independent of k in eq.10? then why do we need fewer delay lines?

p6.144 "This means that each target in the swath shall be (mainly) illuminated only by a part of the chirp" by how much?

p6.ln156. Is scanning on Tx or Rx? if scanning is Rx, how to you time it?

p6ln159. Is B_ch this is not the signal bandwidth in eq 4.?

p7 Figure4. The figure is very small. Increase font. 

p7 The complete discussion is not clear.  Difficult to understand because the basic principles of F-Scan were not well explained .

p14 eq 28 reference?

p16:ln 321 What is bandwidth maximization?

p16 ln 325-328: Authors assumption without numbers to support. You need delay lines and phase shifters. Delay lines are not easy to design for wide bands.  In SCORE you only need a ADC per channel. 

p16 ln 330-340. Does not require too much effort to solve a problem that SCORE could solve?

Author Response

Dear Reviewer,

our response are in the attached file.

The corresponding author,

Pietro Guccione

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

Thank you for the very interesting and well written paper. I have some small comments:

1) For references to equations you use different variants: Eq.X, Eq. X, Eq. (X). Please, check througt whole text and use same style.

2) The same for references to figures.

3) Other comments are in the attached file.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

thank you for your comments. Our answers are below.

The corresponding author,

Pietro Guccione

Author Response File: Author Response.pdf

Reviewer 3 Report

-        The most important concern with this manuscript is the level of contribution. F-SCAN processing is an existing method in the literature and nothing new about it has been added to this manuscript. The authors claim that the design of an f-SCAN acquisition system is applied in the case of an exemplary demanding X-band spaceborne SAR acquisition mode. In this case, what has been added to the literature from a technical/mathematical point of view? It seems that this work is ultimately an incremental or combined work, and its results are only the result of examining the performance of an existing system. If not, authors should clearly explain the significant contribution of their work to its publication as a journal paper or improve the contribution and novelty of the work. Otherwise, in my opinion, the manuscript is not acceptable in Remote Sensing.

-        literature review in its current form is not complete for a full journal paper.

-        Many formulas are presented without references.

-        MatLab → MATLAB

-        Line 359: Please modify sin− 1(·).

Author Response

Dear reviewer,

Thank you for your valuable comments. Our answers are below.

The corresponding authors,

Pietro Guccione

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear authors.

I'd like first to thank you for taking the time to answer all my questions and to consider my comments in your paper.

You have clarified my questions. I think that the way you explain the methodology now is more comprehensible.

You wrote a very interesting article describing a novel technique.

I only have a very small remark. The version I received seems to have been printed from the document that had change tracker because I see changes that appear to have been corrected.

For example, in the abstract I can read "and estimation of IRF and distortion removal are detailed." but appears to be like strikethrough text.

And a small punctuation typo in page 7 line 203 "1/PRF are removed. and the geometric". Thanks again for your efforts

Author Response

Dear reviewer,

please, find attached our answer,

Thank you for your time.

The authors

Author Response File: Author Response.pdf

Reviewer 3 Report

The revised version is improved; however, some responses and actions are still not convincing.

- Contrary to the answer, literature review is still not enough for a full journal paper. A 20-page article has only 19 references! It is necessary for the authors to review the relevant and state-of-the-art works and clearly state their differences and similarities with their own work.

- The article has 33 equations (apart from the formulas in the text). However, only one of them has been referenced. The authors claim to have derived them themselves. I do not believe this, and some formulas are not new formulas. Providing a reference for the equations does not reduce anything from the novelty of the work (or simply not providing a reference does not make the novelty of the work bolder). Providing references can help readers refer to references more easily and understand more details whenever they have doubts. Here again, I point out that the current number of references is insufficient for a full research paper.

Author Response

Dear reviewer,

Thank you for your time and the further suggestions. They helped to improve our paper. Please, attached you will find the answers to your comments.

The authors.

Author Response File: Author Response.pdf