A Novel Method for Improving Quality of Oblique Incidence Sounding Ionograms Based on Eigenspace-Based Beamforming Technology and Capon High-Resolution Range Profile

Round 1

Reviewer 1 Report

In this manuscript authors developed a novel signal processing scheme based on the Capon high-resolution range profile (HRRP) and Eigenspace- Based (ESB) beam forming technology. Without doubts the proposed method is interesting and will potentially useful for improving the ionogram quality and the range resolution of oblique incidence sounding.

The main goal of oblique incidence sounding (OIS) is determining the radio wave propagation conditions for the optimum operation of radio wave communication systems and over-the-horison radars. OIS permits to determine directly the lowest and maximum observable frequencies (LOF and MOF), the maximum usable frequency (MUF), multi-hop mode structures, anomalous propagation modes on the given radio path.

It does not clear for me what does mean the authors’s phrase “The oblique incidence sounding (OIS) is an important means to detect the ionosphere”.

As for critical frequencies (foF2, fxF2, foE etc.), they are determined from vertical incidence sounding (ionosondes). The estimate of the critical frequency from the OIS requires recalculation of the oblique frequency to the vertical one. To perform such precise recalculation there is a need to use ray tracing model. Authors keep in silence how way they plan to get the critical frequencies. It should be certainly clarified in the manuscript. If authors analyze the MOF, it should be clearly identified.

The abstract summarizes the paper and state the main results. All parts of the text, references and figures are necessary for the new results and main points to be understood.

I can recommend the manuscript for publication after revision.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

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Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

The manuscript deals with the improvement of the imaging quality of oblique incidence sounding (OIS) ionograms. The authors proposed a novel signal processing scheme based on the Capon high-resolution range profile (HRRP) and Eigenspace-Based (ESB) beamforming technology. The authors verified the actual effect of the proposed scheme for the OIS ionogram obtained using a transmitter at Leshan station and multi-channel receiving system at Xiantao station in China.

I have a few key remarks about the manuscript:

(i) Recently, the authors are actively involved in the digital processing of OIS ionograms [Liu et al., Sensors, 2019; Liu et al., Remote Sensing, 2020; Zhang et al., IEEE GRLS, 2021]. In this case, it is desirable for the authors to specify the distinctive features of a novel method for the refereed manuscript. This referee’s offer also applies to the section Conclusions, in which there are no more detailed descriptions of new results.

(ii) The receiving antenna (miniaturized "L" array, composed of 6 monopole antennas with the height of 6m and the distance between adjacent antennas of 10m) at Xiantao is installed near the water environment (lake?), namely is working in two different media (water and land). How do such media with their own impedances distort or interfere the reception of HF radio signals?

(iii) In the fifth section, many figures are presented (from Figure 5 until Figure 15) and discussion of the results obtained is absent.

What motives are chosen by authors for selection of three sets of data at different fixed frequency points for testing and comparison: 7.6 MHz, 8.15 MHz, 11.05 MHz?

It may be worth to consider a variant of illustrating a number of Figures as supporting material.

In addition, it would like to know the explanations of the authors about the appearance of 2 traces (or 2 peaks) for case ESB+HR in Figures 11, 12 and in Figure 14.

(iv) For the convenience of readers, please indicate a DOI number for references.

(v) The language needs to be significantly improved.

- For example, there are complex proposals.

More specifically, it can be found that due to the improvement of 81

the SNR of the OIS ionogram and the improvement of the range resolution, the stratifica- 82

tion inside Es-layer or F-layer can be clearly observed, and even the evolution process of 83

different stratification with time.

- roughly --> schematic or other variants

- movement (frequently used by authors) --> motion (occasionally)

 

Minor comments.

a) What is the I/Q data? Please give definition of the term.

b) Different names of the fifth section.

lines 93-94: 5, Experimental results and analysis;

l.235: 5. Experiments and Discussion

c) No date and time for analyzed ionograms (see Figures 9, 11, 13, 14 and 15).

What time is used in Figures 13, 14, local time or universal time?

d) The referee can not accessed following web-page on July 7, 2022 and other days.

http://cnx.rice.edu/content/m10588

Please provide the correct reference.

e) There are two identical citations in the section References (No. 24 & 29).

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I am satisfied by corrections and changes made by authors. I can recommend the manuscript for the publication in the present form.

Author Response

Thank you very much for your affirmation of our work.