Rotational Motion Compensation for ISAR Imaging Based on Minimizing the Residual Norm

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

This manuscript proposes a novel rotational motion compensation algorithm. The proposed method estimates different rotational parameters independently to avoid the issue caused by cumulative errors. The technical route of the paper has certain feasibility, but there are some serious problems as follows:

 

1.      This method requires selecting the dominant range bin with the smallest ANV, and the subsequent steps are all based on the signal in this dominant range bin. However, using only one range bin may introduce estimation errors. And, I believe that the estimation error of the rotation parameters is related to the dominant scatterer you choose. As is known, the Doppler frequency at the rotation center is zero. If the dominant scatterer is located close to the rotation center, its Doppler frequency will be very small. In this case, how can the estimation accuracy be guaranteed?

2.      In the last step, the RMC is completed for signals in all range bins using phi_1 and phi_2. However, different scatterer has different doppler frequency, which means the signal corresponding to different scatterer have different phi_1 and phi_2. How does it work that the RMC can be completed in all range bins with the same phi_1 and phi_2?

 

4.      Furthermore, there are several mistakes need to be modified. For example,

a)        In line 91, the word ‘fast time’ needs to be modified as ‘slow time’.

b)        In formula (3), the R(t) is ignored as compared to formula (1). So that the A_k in formula (3) is different from the A_k in formula (1)?

c)        In line 164 and 165, the symbol ‘t’ needs to be modified to ‘t_m’.

d)        In line 215, what dose ‘B_p’ stands for? There is no explanation.

 

Comments on the Quality of English Language

The expression in English needs improvement.

Author Response

Please see the attachment. Thank you so much!

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

A novel RMC algorithm is proposed in this manuscript to mitigate the impact of cumulative errors. Although several experimental results obtained by applying the proposed method to ideal point scatter target model, full-wave electromagnetic simulation data and actual radar data, demonstrate its effectiveness,  there is a fundamental conceptual error in its theoretical discussion:  “Due to the cyclic feature in the spectral transformation of sampled signals, rotational parameters exhibit periodic ambiguity with a period of 2π [28,29]. Therefore, we can confine the parameters searching space within [−π, π].”

I believe that the phase ambiguity exists in the rotational phase (hp in formula (9)), not in the rotational parameters (φ1 and φ2 in formula (9)).

As this concept is fundamental to the entire algorithm's operation, the manuscript cannot be accepted until this error is corrected.

Moreover, some points that need to be further addressed:

(1)   This manuscript demonstrates the parameter estimation of a second-order phase polynomial. For highly maneuvering targets, the third-order phase cannot be ignored. Please provide additional information on the performance of the proposed algorithm in estimating the parameters of a third-order phase polynomial.

(2)   It can be seen that just one single dominant range bin is selected to for rotational parameters estimating. Selecting multiple dominant range bins may improve the estimation accuracy of rotational parameters. Please verify the correctness of this inference through experiments.

Comments on the Quality of English Language

Further improvement is needed

Author Response

Please see the attachment. Thank you so much!

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has been revised based on the previous review comments. Then, a novel image focusing method for ISAR imaging of targets undergoing non-uniform rotation based on the iterative search method combined with the residual norm criterion after linearly fitting the signal phase is expressed clearly and legibly, which exhibits better focusing effect and higher computational efficiency compared to traditional methods.

Comments on the Quality of English Language

Although most statements can be understood, there are still a few statements that are confusing. such as“rotational parameters exhibit periodic ambiguity with a period of 2π. we can confine the parameter search space within φ1 ∈ [−π, π] and φ2 ∈ [−π/N, π/N]. ” The parameter search space of φ2 is  [−π/N, π/N]  instead of [−π, π],Why?