The paper contains a lot of valuable and high-quality science, which is suitable for publication. I enjoyed reading the material and found the subject matter very interesting. The paper, however, currently contains grammar errors, lacks proper citations, and several figures/captions are missing information. There is currently no mention or analysis of the reliability of the results- (no statistical significance or error analysis associated with the final results). Therefore, I recommend that the manuscript is revised before acceptance. I have made several additional notes as examples of some of the suggested edits in the attached PDF document. Overall, great paper. 

The manuscript studies three methods for detecting seismic ionospheric disturbances and obtains some results. However, the manuscript lacks highlights, and the results and related discussions are not good.

1. There are few explanations related to S4. How to use GNSS or GNSS-RO to obtain S4?  What is the specific response relationship between S4 and earthquake? None of the above issues were explained clearly.

2. The S4 results obtained by GNSS-RO have obvious anomalies before and after the earthquake. Are these anomalies caused by the earthquake or other reasons? Geomagnetic activity? Solar activity? In addition, do the results obtained by the other two methods also consider the causes of geomagnetic activity and solar activity? Relevant data are not analyzed in this paper.

3. What is the correlation coefficient R between the two variables? The correlation coefficient R is less than 0.1.The correlation is too weak and has no practical significance. 

4. There is too little analysis of the results obtained by each method. It seems that it only describes the results without analyzing the physical mechanism behind them.

For the above reasons, I propose to reject this manuscript.