Elevation Spatial Variation Error Compensation in Complex Scene and Elevation Inversion by Autofocus Method in GEO SAR
George Melillos
Round 1
Reviewer 1 Report
The author's submitted a paper describing an autofocus algorithm for GEOSAR missions.
The abstract needs a lot of improvement to summarize what is described in the paper. It is not clear what is the limitations of the algo. Where does it break? Does it cover all cases?
Using the PGA needs at least 2 reference targets at different ranges, and this limits the application of the algo for real scenes. What targets are being used as reference? How accurate you should now it's position.
If the rotation of the satellite and the integration of the aperture is very long. How are you dealing with temporal Decorelation?
How long can be the su apertures before the algo breaks?
What are the orbital errors considered for the simulation? To me it looks very ideal.
How does your algo performs un a real scenario?
How does the algo perform with distributed targets?
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this paper, the authors discussed the compensation of elevation spatial variation error based on RD-ACS method, sub-block method, MD and PGA methods. In general, the topic is very interesting. However, the improvement seems to be very slight. Besides, the papers lack some analysis in detail, and the papers are not well prepared. The reviewer suggests that this paper is rewritten and resubmitted.
- The introduction should be further enhanced. The authors should comprehensively review other papers.
- The authors discussed the elevation spatially variant error in section 3, and the errors were shown in Fig. 2. In general, these errors include two parts, i.e., the phase history error and approximation error introduced by the fifth expansion. The authors should separately discuss both errors. Then, the readers can easily understand which error is the main factor.
- Inspecting Eq. (4), the error is a function of t0, R0 and height. That is to say, the error would be a 3-D figure with different height. With these 3-D error figures, the analysis would be much more helpful.
- In Fig. 2, the authors should explicitly explain the meaning of ‘original phase error’ and ‘fitting phase error’.
- In section 4.1, the sub-block was used by authors. The reviewer wanders to know how to generate the sub-block. The authors should discuss this in detail.
- Line 173 on page 5: The sub-block index Pi is confused with target Pt in Fig. 1.
Besides, some symbols such as q and k in Eq. (6) were not defined.
Line 248: P1 -> P1 and P2
The authors should carefully check the paper to avoid similar issues.
- In Fig. 4, some thresholds such as g1, c1 and c2 were not explained. The authors should clarify how to determine these thresholds.
- Quality parameters such as azimuth resolution, PSLR and ISLR should be used to evaluate imaging results shown in Fig.9 and Fig. 10.
- Based on Fig. 10, the asymmetric side lobe slightly affects the imaging performance. In general, this is a common phenomenon in real data processing. From the reviewer’s view, the sidelobe seriously influencing the mainlobe should be considered. The authors should discuss the serious influence of this phenomenon.
- PGA was used 10 times in section 5. The authors should present some autofocus reresults. Besides, the quality parameters such as azimuth resolution, PSLR and ISLR should also be calculated. With this operation, the readers can visually find the performance improvement in terms of PGA iteration.
- The English in this paper should be further improved.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors present an interesting paper about a process to solve the elevation spatially variant problem in complex scenes and utilize the elevation spatially variant error to inverse the target elevation. The manuscript is well written and should be of great interest to the readers. References could be on a new page. More clearly results. All figures with charts could be bigger. They are not clear.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
After revision, the paper improved. The reviewer suggests that this paper is accepted.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Please fix grammar and spelling mistakes.
Figure 1 seems a bit cluttered and it's hard to interpret what's being conveyed.
Figure 5 has a spelling error "slpoe"...also, should "Dramatic" part be changed to "Dynamic part"?
Is Section 5 depicting an experiment or a simulation? Might want to rename this section "Simulations" if it is the later. Please give a more in-depth i.e. the distance between 'dots', why was a 5x5 matrix chosen? Would it be possible to image an actual real-world structure? Also please provide a magnitude scale showing dynamic range for Figure 10a.
Reviewer 2 Report
Thanks for submitting the paper. I recommend this paper to be submitted after major reviews. In the next lines, I'll add my comments:
- in general, it is not clear what are the limitations of the proposed algorithm. Does it work in all conditions? Is it possible to achieve perfect autofocus in any place on the observed scene?
- please include a discussion on how the algo performs with point-like targets and distributed targets.
- similarly, please add a discussion on how does it perform with highly-directive and isotropic-like targets.
In both cases, pleas compare the impulse response.
- what is the achieved accuracy in phase? I can see it performs good for amplitude (for point like targets) but what about phase?
- what is the required minimum SNR for the algo to converge?
- What type of reference target do you need to achieve the desired resolution/SNR?
Reviewer 3 Report
The manuscript (Manuscript ID: remotesensing-1216842) entitled "Elevation Spatial Variation Error Compensation and Elevation Inverse by Autofocus Method in GEO SAR" seems to possess only a scientific content of incremental value as compared to the previously submitted and accepted article (Manuscript ID: remotesensing-1192941) entitled "Elevation Spatial Variation Analysis and Compensation in GEO SAR Imaging" .
The following reasons justify the similarity between the two manuscripts:
- The words/phrases "Elevation Spatial Variation Error " and "GEO SAR" appear in the keywords of the two manuscripts. The titles also look only incrementally different.
- All of the authors of Manuscript ID: remotesensing-1216842 are also the authors of Manuscript ID: remotesensing-1192941.
- Occurrence of common references in the two manuscripts (References [1], [2], [3], [4], [5], [6], [7], [8], [17], [18], [19], [20], [21], [22] mentioned in Manuscript ID: remotesensing-1216842 are also mentioned in Manuscript ID: remotesensing-1192941 .
- The image for Azimuth compression phase in Fig. 2 of Manuscript ID: remotesensing-1216842 appears like it is a portion of Fig. 5(a) of Manuscript ID: remotesensing-1192941 . The image in the Manuscript ID: remotesensing-1216842 consists of curves corresponding to h = 200 m, 600 m, and 1000 m; whereas the image in Manuscript ID: remotesensing-1192941 consists of curves consisting of h = 200 m, 400 m, 600 m, 800 m and 1000 m. I recommend for the rejection of the manuscript.
The manuscript ( Manuscript ID: remotesensing-1216842 ) lacks sufficient novelty and I recommend for the rejection of the manuscript.
