NOAA Operational Microwave Sounding Radiometer Data Quality Monitoring and Anomaly Assessment Using COSMIC GNSS Radio-Occultation Soundings

Round 1

Reviewer 1 Report

The authors did a decent job describing their work and presenting their results. I have no comments. 

Author Response

Reviewer #1

The authors did a decent job describing their work and presenting their results. I have no comments.

AUTHOR STATEMENT: The authors would like to thank the Reviewer for taking the time to review our manuscript, and the positive feedback about our work.

Reviewer 2 Report

The paper by Iacovazzi  et al. assesses the data quality of NOAA microwave sounders using GNSS Radio Occultation profiles from the COSMIC constellation. The results appear sound and clear, although I found the paper maybe too technical, as one might expect from a technical report. 

GNSS-RO have been found to be an important data source for meteorological analyses, where they are assimilated with strong constraints, as in 4D-VAR. Its direct use as in the current paper carries some problems. On one hand the raw GNSS data (the delay) does not require calibration and has no instrumental drift, on the other hand the inverted data (temperature and humidity) requires significant computation and by itself can lead to relevant uncertainty. This is somewhat acknowledged in the text when commenting the behavior of bias in some channels, and it appears to be the reason of less than clear results in the paper. A more clear discussion of the quality of GNSS-RO as used here might help. A discussion of possible complementary data to get a better benchmark would also be interesting for researchers willing tom pursue similar studies.

Most of the paper discussion, in a technical report style, may be relevant for users of these datasets, although I found it could be written in a more concise style. The conclusions mostly stress the relevance of the quality control methodology presented, list back some bias numbers for different channels, but fail to give relevant general guidance for data users that might come out of the exercise. 

Finally the English is fine and I don'y have specific minor changes to suggest. 

Author Response

Reviewer #2

AUTHOR STATEMENT: The authors would to thank the Reviewer for their review of our manuscript. It is very helpful to our work to hear the perspective of other professionals.

The paper by Iacovazzi et al. assesses the data quality of NOAA microwave sounders using GNSS Radio Occultation profiles from the COSMIC constellation.

1) The results appear sound and clear, although I found the paper maybe too technical, as one might expect from a technical report.

RESPONSE:  The authors adopted a certain belief about the readers. If a reader is sufficiently learned in the subject of satellite product quality integrity monitoring, operational satellite data, and GNSS-RO measurements, then they probably can skip the “Introduction” and “Instruments and Observations” sections and start reading from the “Results and Discussion” section. With the wide distribution of this journal to readers that are not familiar with these topics, the authors are trying to give the reader enough background information and sufficient technical rigor so they don’t have to divert their attention to the provided references.

2) GNSS-RO have been found to be an important data source for meteorological analyses, where they are assimilated with strong constraints, as in 4D-VAR. Its direct use as in the current paper carries some problems. On one hand the raw GNSS data (the delay) does not require calibration and has no instrumental drift, on the other hand the inverted data (temperature and humidity) requires significant computation and by itself can lead to relevant uncertainty.

2.A) This is somewhat acknowledged in the text when commenting the behavior of bias in some channels, and it appears to be the reason of less than clear results in the paper. A more clear discussion of the quality of GNSS-RO as used here might help.

RESPONSE: The authors greatly appreciate this comment, which has led us to dig further to find data on the quality of the COSMIC RO wetPrf soundings. We came across a paper by Wang et. al. (2013) that compared COSMIC RO wetPrf data versus radiosonde data. We find these comparison show similar character to the comparison with operational microwave sounding instruments. We have incorporated these findings into our paper in Line 385-390, Line 399-404, Line 619-620, and Line 627-630.

2.B) A discussion of possible complementary data to get a better benchmark would also be interesting for researchers willing tom pursue similar studies.

RESPONSE: In the Introduction, several reference are given regarding 1) the Simultaneous Nadir Overpass method to detect inter-satellite Ta biases, as well as 2) the use of Numerical Weather Prediction output parameters coupled with the Community Radiative Transfer Model to generate O-B Ta statistics. At the same time, this thread was not revisited anywhere else in the paper. The authors have now added a short paragraph at the end of the conclusions (Line 661 to 665) to acknowledge future work to be undertaken to examine the relative strengths and weaknesses of the legacy methods compared to the method described in this paper.   

3) Most of the paper discussion, in a technical report style, may be relevant for users of these datasets, although I found it could be written in a more concise style. The conclusions mostly stress the relevance of the quality control methodology presented, list back some bias numbers for different channels, but fail to give relevant general guidance for data users that might come out of the exercise.

RESPONSE: This is an astute observation by the Reviewer that needs to be communicated by this study. The authors have created a new Section 4.4 (Lines 571-595) that contains a brief statement to users regarding the lessons learned in this study about using the COSMIC GNSS RO data. The most important lesson learned is also reaffirmed in the Conclusion in Lines 658-660.

4) Finally the English is fine and I don't have specific minor changes to suggest.

RESPONSE: Thank you for checking this.