Comparison of a Bottom-Up GNSS Radio Occultation Method to Measure D- and E-Region Electron Densities with Ionosondes and FIRI

Round 1

Reviewer 1 Report

Review report of the manuscript “Comparison of a Bottom-Up GNSS Radio Occultation Method to Measure D- and E-Region Electron Densities with Ionosondes
and FIRI” by Dylan J. Shaver, Dong L. Wu, Nimalan Swarnalingam, Anthony L. Franz, Eugene V. Dao, and Daniel J. Emmons.

General comments:

In this manuscript, the authors presented a comparison study of a bottom-up radio occultation method to measure D and E-region electron densities with ionosonde and FIRI. The paper is well written and well organized with some interesting case studies. Overall, I found that moderate revision is needed to address the following issues.

1.      Authors must mention the inversion mechanism for the sake of completeness of the paper. Authors have used atmPhs files, therefore, I assume that their inversion is based on carrier phases. To provide complete information about the inversion, a small description (may not be too much) in the methodology should be added.

2.      How does the bottom-up inversion start? In other words, what are the initial conditions for the inversion? In case of the UCAR Abel-inversion, the initial conditions are based on a mathematical relationship with the first LOS TEC.

3.      How did authors adjust the height of GNSS-RO profiles? Did you just shift whole profiles for the altitude? Need some clarification.

4.      Some previous works need to be added in the introduction that are relevant to the GNSS-RO bottomside/improving the Abel-inversions.

Tulasi Ram et al. 2015 (https://link.springer.com/article/10.1007/s10291-015-0491-z)

Sai Gowtam & Tulasi Ram (https://doi.org/10.1016/j.asr.2021.05.008)

5.      How do the virtual height and real height conversion (in the case of Digisonde) errors influence the statistics of the results? Authors need to add a small paragraph about this at the appropriate place with proper literature citing.

Authors may consider revising the manuscript accordingly to further improve the quality of the paper.

Author Response

Thank you for your thorough and thoughtful review.  We have addressed all of your comments in the response attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper carried out a comparison of GNSS RO electron density altitude profile with the ionosonde and the FIRI model at four selected locations. This work is the further work of Wu et al. 2022. The four ionsonde stand for low-latitude, mid-latitude and high-latitude. The peak frequency of E region, peak height of E region and minimum of frequency are studied. The comparison include the altitude profile comparison, average altitude range comparison, f0E, hmE comparison and electron density at each altitude between fmin and hmE comparison. In all, the comparison between GNSS RO and disonde with FIRI is in good agreement. The paper is well written and well organized. It make contributions to the bottom ionosphere, where is less paid attention by community. I recommend the paper to publish in present form    

section2, the author shall provide the error bar of the cosmic RO and ionosonde electron profile. Also, what is the temporal evolution of ionosonde electron profile? Additionally, the author shall provide a sub-section in section 2 to introduce the FIRI model. This model is not that popular compared with other ionosphere models, and is easy to be mixed with another widely used model: IRI  

The author collected the RO profiles inside the 2 degree range of ionosonde location to compare, they shall give the typical number of RO profiles used for these comparison

english is ok

Author Response

Thank you for your thorough and thoughtful review.  We have addressed all of your comments in the response attachment. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments for author File: Comments.pdf

Author Response

Thank you for your thorough and thoughtful review.  We have addressed all of your comments in the response attachment. 

Author Response File: Author Response.pdf