SAR Multi-Angle Observation Method for Multipath Suppression in Enclosed Spaces

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please check the attached PDF.

Comments for author File: Comments.pdf

Author Response

Dear reviewer, we gratefully appreciate for your valuable comment. The revised parts of the paper are highlighted in blue. The following is a detailed reply to your comments.

1: The article is clear and well written. The only minimal suggestion would be to move the conclusions written in the results section to the conclusions section.

Reply: Thanks for your comments. We have moved the conclusions written in the results section to the conclusions section. Moved lines 297 to 299 and 343 to 345 to lines 355 to 357 in the manuscript. Please see the attachment.

Thanks again for your comment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript proposed a multi-angle radar observation method and central vector distance algorithm to suppress the ghost images caused by multipath effects in enclosed spaces. My comments are as follows.

The captions of some figures in the manuscript are too short, more details are suggested to be given for better understanding of these figures.

In Figure 14, for the proposed method’s result (i.e., figure 14 (g)), there are two strong scatters at the up-left corner, and they are stronger than that in the subaperture fusion method. Please explain in the manuscript.

Is the subaperture fusion method is the SOTA algorithm? In Figure 15, the subaperture fusion method obtained result seems worse than the composite image? Maybe more SOTA algorithm should be employed for the comparison to demonstrate the effectiveness of the proposed method.

Author Response

Dear reviewer, we gratefully appreciate for your valuable comment. We have carefully considered your comments and revised them in the manuscript. The revised parts of the paper are highlighted in blue. The following is a detailed reply to your comments.

1: The captions of some figures in the manuscript are too short, more details are suggested to be given for better understanding of these figures.

Reply: Thanks for your comments. We have carefully revised the captions of all figures in the manuscript to provide more detail for better understanding. In addition, the titles of the tables in the manuscript were also checked, and the titles of tables 1, 2, 3, and 7 were provided with details.  

2: In Figure 14, for the proposed method's result (i.e., figure 14 (g)), there are two strong scatters at the up-left corner, and they are stronger than that in the subaperture fusion method. Please explain in the manuscript.

Reply: Thank you so much for your careful check. We have the following two explanations for this problem:  

①：The sub-aperture fusion method will multiply between images. This step makes strong pixels stronger and weak pixels weaker. Our method is to detect ghosts that change with angle and suppress them, without operations on amplitude.

②：The strong scatters mentioned have a stable scattering center, the scattering intensity does not change, and the position does not change with the angle, which is not our main suppress.  

For the above reasons, this does not affect our evaluation of the results. We also add explanations about this problem in the manuscript, between lines 319 and 327.

3: Is the subaperture fusion method is the SOTA algorithm? In Figure 15, the subaperture fusion method obtained result seems worse than the composite image? Maybe more SOTA algorithm should be employed for the comparison to demonstrate the effectiveness of the proposed method.

Reply: Thanks for your comments. Your suggestions are very useful to us.

The sub-aperture fusion method used in the paper is the SOTA algorithm, but compared with the comparison image, the suppression effect is indeed not obvious, and it is not suitable for the scene of this paper. Now we have adopted a new SOTA sub-aperture fusion algorithm: the double-layer sub-aperture fusion algorithm, the first layer multiplies the sub-aperture and the full aperture, and the second layer then groups and adds the multiplied sub-apertures. Comparing the effect of using this method with the composite image shows that this method can effectively suppress multipath. All the simulation experiments and practical experiments in the paper are re-processed by this method, and the SCR are also updated.

It can be seen from the processing results that the double-layer sub-aperture fusion method has the ability to suppress ghosts, but multiplication between sub-image pixels will be performed during the process. Multiplication makes stronger pixels stronger and weaker pixels weaker. Most importantly, this method results in loss of target information.

On the contrary, our method can retain as much target information as possible while effectively suppressing the ghost. In short, the effectiveness of our method is verified by comparing with the new double-layer sub-aperture fusion method.

The problem raised above have been corrected and explained in the manuscript. The new sub-aperture processing results of simulation and practical experiments are modified: Figure 12(e), Figure 13(e), Figure 14(f) and Figure 15(f); the SCR in Tables 6 and 8; text descriptions under each experiment, highlighted in blue. Please see the attachment.

Thanks again for your comment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper a novel multi-angle observation method for SAR radar detection systems. In my opinion, it is necessary to consider several points, as described herein:

 

1. Please check the formulas. The slow time term is missing in equation 2.

 

2. The black text in Figure 12 (a) is not clear with a blue background. It is suggested to change the text color to white in the figure.

 

3. Please add physical units in Table 4 and 5.

 

4. What is the sub-aperture length of the simulation data and the real data? Please provide this information in the paper, as it affects the resolution.

 

5. How is SCR calculated? Please explain clearly in the paper.

 

6. The millimeter-wave radar used in the experiment has two transmit antennas and four receive antennas. How many channels are used in the experiment?

 

7. Can this method be applied to the situation where the observation angles are more than 3?

 

8. There are some grammar errors in this paper. Please read carefully to revise them.

 

Comments on the Quality of English Language

There are some grammar errors in this paper.

Author Response

Dear reviewer, we gratefully appreciate for your valuable comment. The revised parts of the paper are highlighted in blue. The following is a detailed reply to your comments.

1: Please check the formulas. The slow time term is missing in equation 2.

Reply: Thanks for your comments. We modified equation (2) by adding a slow time τ to the equation and moving the complex scattering coefficient that should be within the summation sign to the correct position. The following is the modified equation, with added explanations in lines 101 to 102 of the manuscript.

2: The black text in Figure 12 (a) is not clear with a blue background. It is suggested to change the text color to white in the figure.

Reply: Thanks for your comments. We have modified the text in Figure 12(a) to a white color that is easier to see. In addition, we checked that the same problem existed in Figure 13(a) and modified it together.

3: Please add physical units in Table 4 and 5.

Reply: Thanks for your comments. We have added physical units to Tables 4 and 5.

4: What is the sub-aperture length of the simulation data and the real data? Please provide this information in the paper, as it affects the resolution.

Reply: Thanks for your comments. The sub-aperture length of the simulation data and the real data is 0.1 meters. We have added it to Tables 3 and 7.

5: How is SCR calculated? Please explain clearly in the paper.

Reply: Thanks for your comments. We define SCR as the ratio of the pixel intensity of the target area to the pixel intensity of the ghost area, calculated using the formula (9) added in the paper, and an explanation is given in lines 292 to 294 in the paper.

6: The millimeter-wave radar used in the experiment has two transmit antennas and four receive antennas. How many channels are used in the experiment ?

Reply: Thanks for your comments. We only use date of one receive channel of millimeter wave radar in our experiments, and added this in Table 7.  

7: Can this method be applied to the situation where the observation angles are more than 3?

Reply: Thanks for your comments. This method is suitable for situations with more than three angles. This article takes three angles as an example. Explain in lines 86 to 87 of the manuscript.

8: There are some grammar errors in this paper. Please read carefully to revise them.

Reply: Thanks for your comments. We have carefully checked and revised the grammar in the paper from beginning to end.

Please see the attachment. Thanks again for your comment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I have no more comment for the manuscript.