Using the Commercial GNSS RO Spire Data in the Neutral Atmosphere for Climate and Weather Prediction Studies

Round 1

Reviewer 1 Report

The paper entitled, ‘Using the Commercial RO Spire Data in the Neutral Atmosphere for Climate and Weather Prediction Studies’ present’s important work and results for an adequate field. After my thorough reading, I have not found any vague statements or blatant mistakes, which prompt me on a negative decision. I suggest the paper is good to publish in ‘Remote Sensing Journal’. The results match the contemporary issues in a good way by addressing the lack of problems in previous report. Therefore, I am recommending it for publication, only after adding the below minor suggestions.

The title needs to change and introduce GNSS RO there

Lines 13. Is it possible to write RO data of GNSS?

Lines 15. CDWP is same as Line 14 or different?

Keywords has no GNSS? Why?

Line 40. Is this the right way to start a sentence with references?

Line 43. Replace ‘satellite infrared (IR) and microwave (MW) sensors’ by ‘Satellite Infrared (IR) and Micro Wave (MW) sensors’.

Line 93-107. Some ‘;’ are inappropriately used. Please correct.

Line 176 & line 180. Somewhere it is Figure and somewhere Fig? Uniform all

The url used are not as per MDPI format.

Line 304. This notion ‘’ has some special meaning?

Figure 6. Write latitude and longitude on the figure and check for all other figures also.

Table 1 caption must be on the top?

Conclusions need to be separate to summarize the problem and it solution.

Check accuracy of referencing style and please discuss more articles among from international people literature.

Minor English corrections needed.

Author Response

Response to Reviewer#1’s Comments

 

Comments and Suggestions for Authors

The paper entitled, ‘Using the Commercial RO Spire Data in the Neutral Atmosphere for Climate and Weather Prediction Studies’ present’s important work and results for an adequate field. After my thorough reading, I have not found any vague statements or blatant mistakes, which prompt me on a negative decision. I suggest the paper is good to publish in ‘Remote Sensing Journal’. The results match the contemporary issues in a good way by addressing the lack of problems in previous report. Therefore, I am recommending it for publication, only after adding the below minor suggestions.

 

• Thanks for the comments. Here we respond to each of the comment below.

 

1. The title needs to change and introduce GNSS RO there

 

• “GNSS” is added to the title.

 

2. Lines 13. Is it possible to write RO data of GNSS?

 

• I assume you meant line 18. “GNSS RO data” is better.

 

3. Lines 15. CDWP is same as Line 14 or different?

 

• The CDWP in line 15 is the same as the CDWP in line 14.

 

4. Keywords has no GNSS? Why?

 

• We add “Global Navigation Satellite System” in the keywords.

 

5. Line 40. Is this the right way to start a sentence with references?

 

• We replace “[4] and [5]” with “Studies in [4] and [5]”.

 

6. Line 43. Replace ‘satellite infrared (IR) and microwave (MW) sensors’ by ‘Satellite Infrared (IR) and Micro Wave (MW) sensors’.

 

• We used “satellite Infrared (IR) and Microwave (MW) sensors”

 

7. Line 93-107. Some ‘;’ are inappropriately used. Please correct.

 

• There are no “;” between 93-107. Nothing is changed.

 

8. Line 176 & line 180. Somewhere it is Figure and somewhere Fig? Uniform all

 

• We replace the “Fig.” with “Figure” through this paper.

 

9. The url used are not as per MDPI format.

 

• In line 280, we use “(0, https://rda.ucar.edu/datasets/ds351.0, accessed on 20 July 2023)”

10. Line 304. This notion ‘’ has some special meaning?

 

• We did not see any ‘ ‘ in line 304 and the in the section. Nothing is changed.

 

11. Figure 6. Write latitude and longitude on the figure and check for all other figures also.

 

• We add “Latitude” and “Longitude” on the Figure 6.

 

12. Table 1 caption must be on the top?

 

• We moved Table 1 caption on the top.

 

13. Conclusions need to be separate to summarize the problem and it solution.

 

• We also follow the suggestion from Remote Sensing to separate the final “Conclusions and discussion section into two sections. In line 186, we add “We discussed the results in Section 6 and concluded this paper in Section 7.”

 

14. Check accuracy of referencing style and please discuss more articles among from international people literature.

 

• We check all the references and use the reference style used by the Remote Sensing.
• We also add several other references recently published by international RO community on this topic.

 

15. Comments on the Quality of English Language Minor English corrections needed.

 

• We check the writing carefully and made several minor revisions. Dr. Miller (one of the co-authors), who is a native English speaker, also helped checking the English writing to ensure the writing quality of this paper.

 

 

Reviewer 2 Report

Comments on a manuscript entitled “Using the Commercial RO Spire Data in the Neutral Atmosphere for Climate and Weather Prediction Studies.” by Ho, S -P, et al.      

 

This study demonstrates the quality of Spire RO data products for weather and climate applications. Multiple comparisons are made with Spire RO data from different sources, including COSMIC-2, ECMWF reanalysis ERA-5 products, and radiosonde observations to quantify the data quality. The authors demonstrated with lower Signal-Noise-Ratio, the pattern of the lowest penetration height for Spire is similar to those for COSMIC-2. And the retrieval accuracy from Spire is very compatible with those from COSMIC-2. In addition, their results showed that the COSMIC-2 estimated error covariance values are more significant over the oceans at the mid-latitudes. It is well known, and the authors also mentioned the importance of RO observation and its higher impact on initializing numerical weather prediction and data assimilation. In addition, RO observation plays a significant role, and the observation impact is very high in any regional or global data assimilation (DA) system. The results and the study are important and interesting. The manuscript is well written and is ready for publication after minor revision.

  

General comments:

 

1. Line 57 and Line 163-164. Change the font style to maintain a uniform manner.

 

2. Line 165, “… Spire BA….”. What is the meaning of BA? Is it a Bending angle? Specify the complete form.

 

3. Line 93-107 and line 115, why are there multiple green highlighted points? Remove those green highlighters.

 

4. In Figure 3a, I can not see any spire observations over the region approximately. 30N-60N and 5E-45E, and in Figure 3c, KOMPSAT-5 observations gap over many regions, particularly the region approx. 30S-60N and 30E-95E. What are the many scientific reasons for those data gaps? 

 

5. Figure 3b and over the equatorial region shows uniform ups and downs in the number of COSMIC-2 observations. Why such kind of patterns for this kind of observation? 

 

6. More accurate observation error is essential for any data assimilation community and needs to be known correctly. The results and the study are significant and interesting. The author should mention the mean observation error for the spire data horizontally and vertically and for each parameter in a separate table. In particle observation, error range for Spire bending angle and reflectivity.

 

7. Finally, what specific improvements should the authors consider regarding the STAR spire data processing methodology?

Author Response

Response to Reviewer#2’s Comments

 

Comments on a manuscript entitled “Using the Commercial RO Spire Data in the Neutral Atmosphere for Climate and Weather Prediction Studies.” by Ho, S -P, et al.      

 

This study demonstrates the quality of Spire RO data products for weather and climate applications. Multiple comparisons are made with Spire RO data from different sources, including COSMIC-2, ECMWF reanalysis ERA-5 products, and radiosonde observations to quantify the data quality. The authors demonstrated with lower Signal-Noise-Ratio, the pattern of the lowest penetration height for Spire is similar to those for COSMIC-2. And the retrieval accuracy from Spire is very compatible with those from COSMIC-2. In addition, their results showed that the COSMIC-2 estimated error covariance values are more significant over the oceans at the mid-latitudes. It is well known, and the authors also mentioned the importance of RO observation and its higher impact on initializing numerical weather prediction and data assimilation. In addition, RO observation plays a significant role, and the observation impact is very high in any regional or global data assimilation (DA) system. The results and the study are important and interesting. The manuscript is well written and is ready for publication after minor revision.

 

• Thanks for the comments. Here we respond to each of the comment below.

  

General comments:

 

1. Line 57 and Line 163-164. Change the font style to maintain a uniform manner.

 

• We checked the font style of line 57 and 163-164 and change the font style to ensure the consistent font style is used.

 

2. Line 165, “… Spire BA….”. What is the meaning of BA? Is it a Bending angle? Specify the complete form.

 

• Yes, “BA” is “Bending angle” and we mentioned that in Line 107.
•  

3. Line 93-107 and line 115, why are there multiple green highlighted points? Remove those green highlighters.

 

• All highlights from line 93 to 107 and line 115 are removed.

4. In Figure 3a, I can not see any spire observations over the region approximately. 30N-60N and 5E-45E, and in Figure 3c, KOMPSAT-5 observations gap over many regions, particularly the region approx. 30S-60N and 30E-95E. What are the many scientific reasons for those data gaps? 

 

 

• I assume you are talking about Figure 2a. Please see the attached news at https://bnr.bg/en/post/101763096/because-of-the-war-in-ukraine-there-are-problems-with-the-gps-signal-along-bulgarian-black-sea-coast. The news indicates that GPS not working well in this region because of war. 

 

• In line 358, we add “. Please note that the less Spire observation number over Eastern Europe, particularly in the region bounded by 60°N-30°N and 30°E and 45°E as shown in Figure 2a, is primarily attributed to the adverse conditions resulting from Russo-Ukrainian conflict, which have led to poor performance of GPS/GALILEO signals in this area.”

 

• KOMPSAT-5started operation in 2013 in a sun-synchronous orbitof altitude 550 km, inclination 98.1°, and LST (Local Solar Time) of 0600 hours (dawn-dusk orbit). Our RO occurrence prediction for KOMPSAT-5 and GPS (Figure 1) shows a more uniform distribution of the RO sounding opportunities than the actual occurrence map shown in Figure 2b of the paper. Our speculation of the less RO occurrence over the 30S-60N and 30E-95E region is due to the aging of the RO/GPS receiver of KOMSAT-5. The small-scale irregularities of ionospheric electron density (plasma bubbles) can cause GNSS signal scintillation. The GNSS signal can be diffracted and refracted in the ionospheric irregularities, leading to GPS signal amplitude, phase scintillations, and increased noise. The dawn and dusk terminator regions are a moving boundary between day and night on the Earth, a substantial source of perturbations and irregularities in the ionosphere. During geomagnetic storms, these ionospheric irregularities and perturbations occur more frequently, which can trigger GNSS signal scintillation. Figure 2 shows the GNSS scintillation occurrence map during a geomagnetic storm. The region over 30S-60N and 30E-95E falls into the frequent GNSS scintillation occurrence region in the Eastern globe. The frequent GNSS scintillation occurrence region moves to South America in the western globe due to the geomagnetic minimum in the South Atlantic region.

 

On the other hand, the retrieval of RO profiles is also challenged by multi-path due to sharp gradients in the moisture-rich lower troposphere. The occurrence of moisture-rich lower troposphere is within the Inter-Tropical Convergence Zone (ICTZ) near the Equator. The aging KOMPSAT-5 receiver, i.e., degraded low-noise amplifier (LNA), has degraded signal gain, making it challenging to receive good quality GPS signal under dawn-dusk ionospheric perturbations and multi-path problems in moisture-rich regions. Therefore, we speculate that the degraded KOMSAT-5 receiver performance over the interception of ionosphere perturbation/irregularity map and equatorial moisture-rich region map can result in much less RO data over the 30S-60N and 30E-95E region.

 

Figure 1: Predicted KOMPSAT-5 and GPS RO limb sounding opportunities over four months (2023-01 to 2023-04).

• Figure 2. Example of GPS error map due to ionospheric scintillation during a geomagnetic storm. (https://www.swpc.noaa.gov/sites/default/files/images/u33/%281100%29%20Equatorial%20Scintillation%20Impact%20on%20GNSS%20services%20%28YM_20170504%29.pdf)

 

5. Figure 3b and over the equatorial region shows uniform ups and downs in the number of COSMIC-2 observations. Why such kind of patterns for this kind of observation? 

 

• This is a very good question, and it is not easy to answer. Figure 1 below shows the predicted COSMIC-2 vs. 31 GPS satellites RO limb sounding occurrence map over six months. The highest RO occurrences are located at four discrete locations along the longitude for each GPS satellite. This is mainly because the orbital period of GPS is 12 hours. There are four equator crossings at the same four longitudes each day for each GPS satellite (See Figure 2). COSMIC-2 orbital period is about 97 minutes. Near the equatorial region, GPS moves much slower than COSMIC-2. When a GPS satellite is near the tropical region around one longitude, the RO occultation will be dominantly located around this longitude. The asymmetric distribution of the occurrences around the Equator is due to the 55-degree versus 24-degree orbital plane inclination angle of GPS and COSMIC-2 satellites, respectively. Summing the RO occurrence maps between COSMIC-2 versus all GPS satellites, i.e., panels in Figure 1, the combined occurrence map thus shows the zigzag pattern near the Equator.

 

Figure 1: Predicted COSMIC-2 vs. 31 GPS satellites RO limb sounding occurrence map over six months. The GPS satellite IDs (NORAD Catalog Number) are listed in the top left corner of each panel.

Figure 2: The ground locations of GPS satellite orbits over one month. The last satellite (sat55268) is a backup GPS satellite whose orbit drifts.

 

 

6. More accurate observation error is essential for any data assimilation community and needs to be known correctly. The results and the study are significant and interesting. The author should mention the mean observation error for the spire data horizontally and vertically and for each parameter in a separate table. In particle observation, error range for Spire bending angle and reflectivity.

 

• The best comparisons for the Spire-COSMIC-2 SRO pairs relative to the same references are shown in Fig. 15. The mean fractional BA difference and the standard deviation for the Spire-ERA5 and COSMIC-2-ERA5 are summarized in each panel. Although we did not provide a Table, one can see that the Spire-ERA5 mean biases and STDs are very consistent with those from COSMIC-2 – ERA5. Because we already have seven Tables, we do not provide another Table (for Figure 15) to summarize the mean difference and STDs for the Spire-ERA5 and COSMIC-2-ERA5 comparisons.

 

7. Finally, what specific improvements should the authors consider regarding the STAR spire data processing methodology?

 

• In line 281, we specifically mentioned the reason to compare UCAR Spire data products with those from STAR “ [23-25] suggested the best approach to quantify the retrieval accuracy and uncertainty of one RO mission is to compare it with independent retrievals from another RO mission and compare the RO-RO pairs with other references.” Although it is not explicitly mentioned in this paper, we are considering using the UMD-processed Spire excess phases as inputs for testing the STAR FSI inversion package. That is for a future study and is not further mentioned in this paper.

 

 

Reviewer 3 Report

See attached pdf file.

Comments for author File: Comments.pdf

Requires a professional editing

Author Response

I attach my responses in a word file.

Author Response File: Author Response.docx

Reviewer 4 Report

This paper studied the neutral atmosphere for climate and weather prediction. Good results were achieved. The following issues must be addressed before publication: The manuscript may be considered for publication after a minor revision.

 

1.      The format of Table 1 is inconsistent with the others, please check. Also, the table head should be above the table.

2.      Page 2: line 93 to 107: there are some green highlighting, please check it.

3.      Equation (1) should be mentioned in the main text and given the references.

4.      The clarity of Figures should be improved, and vector graphics are recommended.

5.      Minor editing of English language required.

 

 

Minor editing of English language required

Author Response

Response to Reviewer#4’s Comments

 

Comments and Suggestions for Authors

This paper studied the neutral atmosphere for climate and weather prediction. Good results were achieved. The following issues must be addressed before publication: The manuscript may be considered for publication after a minor revision.

 

• Thanks for the comments. Here we respond to each of the comment below.

 

1. The format of Table 1 is inconsistent with the others, please check. Also, the table head should be above the table.

• We put caption of Table 1 on top. To make Table 1 consistent with other Tables, we also add the unit “km” behind each value.

2. Page 2: line 93 to 107: there are some green highlighting, please check it.

• All highlights from line 93 to 107 are removed.

 

3. Equation (1)should be mentioned in the main text and given the 

• In line 742 (nrew line 1285), we add “Equation (1) shows that under the assumption”

4. Theclarity of Figures should be improved, and vector graphics are 

• We re-generate Figure 6 and add “Latitude” and “Longitude” in the Figures. We also add a new figure in the section 3. Figures 8-12 are in height. To be consistent, we revised the caption for Figures 8 and 9 as “Height (km).” We also re-generate Figures 14 and 18.

5. Minor editing of English language required.

• We check the writing carefully and made several minor revisions. Dr. Miller (one of the co-authors), who is a native English speaker, also helped checking the English writing to ensure the writing quality of this paper.

Round 2

Reviewer 3 Report

The authors have addressed my concerns in their revised manuscript.

Minor editing of English language required