In-Orbit Operational Parameter Calculation and Performance Optimization in KOMPSAT-6 Synthetic Aperture Radar

Round 1

Reviewer 1 Report

The authors propose a method to project the operational parameters of the synthetic-aperture radar (SAR) of the Korean Multi-purpose Satellite (KOMPSAT). Specifically, the pulse repetition frequency (PRF) is considered to calculate the actual parameters for the predicted altitude. The PRF is determined using a nominal altitude and subsequently optimized as the in-orbit altitude changes from the nominal altitude. The proposed method does not overload the SAR controller, so the on-board optimization of the PRF allows a real-time operation of the SAR satellite. Computational simulations are used to highlight the efficiency of the proposed solution. It seems to have better performance than the usual SAR methods, such as those used in KOMPSAT.

The subject is current and relevant. The paper deals with one part of a broad and technologically sophisticated engineering project; therefore, there are many requirements and general aspects to be taken into account. However, the structure of the paper was very well organized, and this made it easier to get a general sense of the context in which the methods for SAR parameter optimization are proposed.

Next, I list some suggestions that in my opinion may facilitate the understanding of the proposed solution:

- I understand that the plot in Figure 1 (osculating orbit) shows predicted values of altitude along the days. However, the points associated with the values are interconnected and very close to each other, which can make it difficult to understand what one really wants to show. What is presented gives the idea of a region in the plane and not a curve.

- As one of the advantages of the proposed method is the fact that it does not overload the SAR controller, it would be appropriate to compare the computational cost of the proposed method with the computational cost of other standard methods.

- In the flowchart shown in Figure 18, it would be convenient to precisely indicate where the "equation for SAR Geometry" and "equation for PRF optimization" are in the paper.

- In what sense is the "optimization" carried through in this paper? Is it a heuristic approach, or is there a way to prove that the derived optimization expressions will always yield a valid solution? This could be pointed out by the authors.

Author Response

Please see the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript, the authors determine upper and lower bounds on the pulse repetition frequency (PRF) in SAR imaging to try to keep the range and azimuth ambiguity low.  This leads to better quality SAR images.  I feel the paper was technically strong and that it is worthy of publication.  There were a few isolated English errors, e.g., line 55 "depends" should be "depend" and on line 78, "imposes another constraint to" should read "impose another constraint on".  Also on line 365, "realized in a real" should read "realized in real".  

Although some plots were presented sohwing the dependence of range ambiguity and azimuth ambiguity on incidence angle, it would be good to have a simulated real-world surface, and then compare the SAR images obtained by simulating the imaging on this surface with the proposed method for PRF selection vs. choosing a fixed PRF or using other methods to adapt the PRF.  This may be difficult to do, but would add immensely to the quality of the paper.

Author Response

Please see the attached file.

Author Response File: Author Response.docx