Ionospheric Clutter Suppression with an Auxiliary Crossed-Loop Antenna in a High-Frequency Radar for Sea Surface Remote Sensing

Round 1

Reviewer 1 Report

General comments

The presented article has a high scientific interest. The tools presented to improve the quality of the signal received from the antennas and their application to improve the measurements of surface ocean currents are of great scientific interest. However, the work can be improved in some respects. Here are some comments that may help the authors and raise some questions about which I have doubts.

Language and grammar: generally, the manuscript is well written. The text is clearly understood, however, English is not my main language, so I do not feel fully qualified to judge about the English language and style.

Title: the title reflects most of the author guidelines in the manuscript.

Abstract: the abstract presents a good summary of the manuscript. The context of the study is clearly defined. However, in lines 20 and 21 it is concluded that the precision of oceanographic currents has been verified with data from GlobCurrent. This conclusion should be revised or rewritten, since a clear graph is not really presented where this result is observed (more details are explained later).

Introduction: well written and exhaustive, however, in my opinion, the last paragraph should be rewritten. From lines 63 to 69 the authors go into too much rather methodological detail. In this paragraph you should simply talk about the general structure that the article will follow. (The authors should comment on these details in other sections of the manuscript).

Signal Model and Adaptative Filter: In my opinion, this section is well written and structured, however, the authors might consider some suggestions in order to clarify some issues:

-Figure 1: the meaning of subscripts 1 and 2 could be indicated

-Line 80: the authors define that φ is the angle of elevation, however in their article [16], when they clarify the same expressions, they define φ as “zenith angle (0 correspond to the zenith)”, perhaps it is more complete and clearer to define φ in this last way.

- Line 84 the authors could define what the subscripts 0 and 1 mean.

- A curiosity... what is the radar sampling interval? perhaps it is interesting to clarify.

 

 

 

 

 

Experimental Results:

 System Parameters

- Line 105: is it possible that clutters has been detected in a range of -1 to 0.5 Hz and not -0.1 to 0.5 Hz?

-In order to clarify the figure 2, the authors could indicate the magnitude and units of the color scale

Detection of Ionospheric Clutter

-Could the authors explain if figure 3 is any example of a signal (with and without clutter) or if it is a signal belonging to the study period? It would be interesting if the signal belonged to the study period.

 

RLS Adaptative Filter

I have an important question: in line 136 the authors indicate that the series in figure 4 correspond to 0:57 on April 1, however, figure 2 (where the clutter is also illustrated) corresponds to 1:15 on April 1. It is not clear to me why different instants of time are used to analyze and show the same phenomenon, could you clarify it?

- The resolution in figure 4 (b) is too low, the authors should improve it.

 

Recovered current map:

-The resolution in figure 10 is too low, the authors should improve it.

-The text in figure 10 (c) is confusing, in my opinion it should indicate “The HFSWR radial current at 01:15 and GlobCurrent radial at current at 00:00”.

About figures 10 (c) and 11, as well as the results derived from them, I have several observations.

-Figure 10 (c) supposes the main application to the development of the treatment of the signal proposed in the work. As the authors say, radars are a fundamental tool in understanding surface ocean currents. These surface currents are not easy to detect with other oceanographic instruments and therefore this work has great potential. However, the results shown in Figures 10 (c) and 11 are not too conclusive.

 

In figure 10 (c) the result to be illustrated is not clearly observed. Do the authors want to illustrate that the applied methodology improves the scope of the current data (a larger area of ​​data is covered)? Do the authors intend to illustrate that quality (data accuracy) improves? What exactly is intended? Really this graph should be absolutely clear and convincing and then the manuscript will acquire much more quality. I suggest a figure with light vectors, and perhaps different colors to illustrate the results obtained before and after the signal treatment. A big and clear figure would be nice.

Likewise, the results and conclusions regarding the improvement of the currents would also be reconsidered. For example, on line 20 (abstract), the authors say:  “The accuracy of the current speed is verified by GlobCurrent data.” but this result is not clear in figure 10 and 11. On the other hand, in line 67 and 68 the authors state: "the gaps on the current map due to the clutter can be filled up." So the question is: what is really (concretely) the improvement that the application of the new signal analysis methodology brings to the stream data?

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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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have worked on all the suggestions for improvement that I indicated, they have answered all my doubts and have corrected some small errors.