Modulation Linearization Technique for FM/CW SAR Image Processing Using Range Migration

Round 1

Reviewer 1 Report

The article refers to the RMA method and the phase resampling method. These methods are known and described in the literature. There is no clear description of the novelty introduced by the authors. In the work "Correcting nonlinear modulation error in linear FMCW radar systems" DOI: 10.1109 / RADAR.2017.7944459, the author gives the focusing method as a way to determine the phase error. This method is also used in this publication. What's new here? In addition, lines 182 - 185 incorrectly describe Figure 7 and the description of Figure 5 here raises doubts. 

Author Response

Thank you for pointing these issues out and they should have been explained better in the first submission.

We did not mean to imply RMA is new. We added more explanation of how the innovation here integrates with RMA at little to no increase in computation time or cost. I hope the explanation is adequate. The new text can be found in lines 188-190 and in the conclusions in lines 285-285

This paper is not about determining phase error, but a new way to use what was found in the Stolt Transform. I revised the manuscript and I hope I explained our method better. The new explanation can be found in lines 96 to 108. 

Reviewer 2 Report

Dear Respected Authors, please find the following remarks.

 

Introduction:

Please follow the Instruction for Authors. There is not sufficient literature review.

The current state of the research field should be reviewed in the meaning of methods of linearization. The other methods pointed in the references should be briefly described and assessed.

Additionally, I recommend to add the following references and shortly describe them in the text showing why your solution is better:

1. Non-Linearity Compensation Algorithm for FMCW SAR, http://dx.doi.org/10.1109/APSYM50265.2020.9350685
2. Novel Nonlinearity Correction Algorithm for FMCW Radar Systems for Optimal Range Accuracy and Improved Multitarget Detection Capability, https://doi.org/10.3390/electronics8111290

I recommend to add the following references the introduction in suitable places:

3. Stolt migration, Fast simultaneous seismic source separation using Stolt migration and demigration operators , https://doi.org/10.1190/geo2015-0044.1
4. SAR algorithms, In-depth High-Resolution SAR Imaging Using Omega-k Applied to FMCW Systems, doi: 10.1109/RADAR.2012.6212233.

Further remarks to the Introduction:

• Fig. 1 a) there is no receiver block marked (Rx),
• Fig 1 b) there are some numbers and units – there is no explanation why these numbers. Is it an example ? Why this one ? Please explain in the text.
• Finally, do you mean Stoltz or Stolt ?

 

Other remarks:

Line 202 – there is Fig. 13 addressed but there is no such a figure.

Please add to the Results or Conclusion the discussion about the advantages of your solution compared to the others. Is your method range or velocity dependant ?  How long the correction factors (let call it a calibration) are valid ? What about situation when the VCO tuning characteristic is not stable i.e. is temperature dependant ? Please add this information to the text.

 

References :

Please check carefully all the descriptions e.g. no 18 - no page count., the reference 12 is a typing mistake, etc.

Reference 17 is a self-citation

Author Response

Thank you for the review and detailed feedback. It is appreciated very much.

We revised the manuscript to better explain the previous art and why our method is better. These changes can be found in lines 57-76, 97-108, 188-190, and 256-285. We hope these additions are sufficient. 

The four references listed in your review were read and added to the literature survey and cited in the text. 

The label RX was added to Figure 1a.

An explanation of Figure 1b as an example waveform was added in lines 25-27.

I removed the self-citation. 

You are correct in questioning the VCO stability over temperature, time, and small circuit changes (such as power supply voltage or VSWR). We attempted to qualify the applicability of the calibration with the caution that the factors you listed can make the calibration less effective or invalid. These statements can be found in lines 262-284. In addition, we stated the applicability of the method over all ranges (as compared to other methods) in lines 261-262 and to a lesser extent in lines 101-107.

The references have been completely revised, renumbered, and corrected which was unprofessional and should have been done correctly the first time. 

Round 2

Reviewer 1 Report

Clarifications have been taken into account 

Author Response

We have clarified some terms.

Reviewer 2 Report

Thank you for adressing the comments. Your explanations in the cover letter have the line numbers not correct in some places, I think, but the overall quality of the paper is now satisfying.

Author Response

We corrected the references again.