Simulation Calculation of Element Number Density in the Earth’s Atmosphere Based on X-ray Occultation Sounding
Round 1
Reviewer 1 Report
The paper is devoted to simulation of the density of elements nitrogen (N) and Oxygen (O) in the range from 120 to 250 km using an X-ray occultation of the Crab Nebula. This information is important for monitoring the ionosphere and thermosphere. In the simulation, the authors use MCMC algorithm for the retrieval of the density from the measured energy spectrum. The results are compared with the standard NRLMSISE-00 model. It was found that the best accuracy can be obtained in the altitude range from 140 to 200 km. At lower altitudes, the errors and inconsistency with the model become large due to low SNR. At altitudes above 200 km, the method does not work well because of the very low density of the elements. Unfortunately the presentation of these key points is not very clear in the paper (see comments below). A revision is required before further consideration for publication.
Comments:
1. Line 83: What is “the initial value”?
2. Equation (3): What is I(E,h)?
3. Line 120: “Due to the limitation of signal to noise ratio” – what is this SNR limitation? Please explain.
4. Lines 168–170: “About” 90% of the X-ray emission…” This sentence should be rather in the Introduction Section.
5. Lines 172-175 “Figure 5 shows the comparison…” Why is this sentence located in Conclusion? Perhaps the Section should be entitled Discussion and Summary.
Typos:
Table 1: Ap (2nT) should be replaced with Ap (nT)
Author Response
Thanks to the reviewer’s comprehensive summary of the work and inspiring comments. The manuscript has been revised carefully based on the received comments. For details, please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This article is devoted to the use of X-ray occultations to study the oxygen and nitrogen content in the upper Earth’s atmosphere. The model problem is solved with the parameters of the NICER telescope, but the data from the telescope onboard the International Space Station were not utilized due to the inappropriate geometry of its observations. The mathematical implementation looks correct and promising, but, in my opinion, the physical interpretation should be clearer and more detailed. The respective explanations are provided in the attached file. In particular, the use of the F10.7 solar flux as 163 sfu seems questionable because the value is close to the maximal monthly ones in the Solar Cycle 24 and significantly exceeds typical values in 2020, the date of which is set during the simulation (Table 1).
Therefore, I assume that the article can be published after major revision.
Comments for author File: 
Comments.pdf
Author Response
Thanks to the reviewer’s comprehensive summary of the work and inspiring comments. The manuscript has been revised carefully based on the received comments. For details, please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
A lot of work was done over the incomplete two weeks. I can note that such a significant improvement is rarely realized during in such a short time. In particular, simulation with corrected parameters of solar activity was provided and physical interpretation was extended. Therefore, the ideas of the article and the scientific level of their implementation allow it to be published in Remote Sensing without changes in the content.
Technical errors in the text are practically absent. Nevertheless, there is one noticeable flaw in the new version: the list of references and their numbers have disappeared from the text. Due to the absence of serious errors in the references in the previous version, this issue can be resolved in interaction with the editors without the involvement of referees.
Several specific remarks:
L. 24. ‘[? ]’ – all the reference numbers are not displayed in the current text.
Table 2. The right columns for background B are not visible here.
L. 185. ‘the energy band of detector need to contain’ – should be in the singular form, ‘needs’.
There is no reference list.
Author Response
Thanks to the reviewer’s comprehensive summary of the revised version and inspiring comments. The manuscript has been revised carefully based on the received comments. For details, please see the responses and revised version submitted.
Author Response File: Author Response.docx
