Assessment of Hongtu-1 Multi-Static X-Band SAR Constellation Interferometry

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper is well written. The authors describe the processing steps performed for the assessment of multi-static X-band SAR constellation interferometry.

There are two issues to discuss with the authors.

1. In line 121-122. "For each of the four SLCs we considered the image spectrum and determined the Doppler Centroid". Could the authors give more description or references, how to consider the spectrum and determine doppler centroid. PIESAT provided SLCs and orbit data with no echoes data, right?

2. Could the authors give description on discussion about the baseline estimation or calibration? Is the current orbit data accurate enough for DEM products.As we all know, a dedicated baseline calibration was perform for Tandem-X, there are systematic baseline errors in Tandem-X. In current processing, is the baseline error is estimated and compensate by the "orbital phase". Perhaps this is not the topic of this paper, but I hope the authors could give some suggestions or opinions on bi- or multi-static SAR constellation's baseline calibration or multi-baseline calibration.

Author Response

"Please see the attachment." 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The paper evaluates the interference capability of the HONGTU-1 constellation simultaneously acquiring one mono-static and three bi-static SAR scenes. It calculated height differences relative to the Copernicus DEM and pointed out that the elevation differences are mainly caused by temporal changes in forests, mining areas. And the paper investigated possible applications about forest can be recognized by its reduced single-pass coherence values.

But there are some issues with this paper：

1.      When estimating the height of altitude change maps generated from multiple different baselines, this article introduces various existing multi baseline estimation methods. However, the article uses the direct averaging method, which only explains the advantages of this approach. The article skips the analysis of the shortcomings of this method compared to other methods. It is hoped that a few examples can be used to illustrate that this averaging method has no significant impact on DEM quality.

2.      Copernicus DEM is relatively older and has a much lower resolution compared to HONGTU-1 data, making it less persuasive for evaluating HONGTU-1 data. Suggest adding other elevation data (such as TanDEM) to demonstrate the accuracy of HONGTU-1 DEM.

3.      Suggest providing a specific formula for the coherence in section 2.7.

4.      Figure 9 shows the trend of forest region correlation under different baselines, but does not indicate whether this is an overall trend or single point data. It is hoped that the overall coherence curve of the forest region and some single point data can be provided in the figure at the same time.

Author Response

"Please see the attachment." 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

 

This manuscript focuses on the Assessment of HONGTU-1 Multi-Static X-band SAR Constellation Interferometry. The authors have good experience and methods in processing of interferometric SAR data, and the analysis of HT1 interferometric data is also novel, and some interesting and useful conclusions are obtained. It is suggested to improve the readability and standardization of the manuscript further.

1. References 15-17 are missing in the Introduction

2. Whether Figure 1 is named SAR image or backscatter could be further considered

3. The color bar is missing in Figures 2 and 3

 

 

 

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

"Please see the attachment." 

Author Response File: Author Response.docx