Preflight Evaluation of the Environmental Trace Gases Monitoring Instrument with Nadir and Limb Modes (EMI-NL) Based on Measurements of Standard NO₂ Sample Gas

Round 1

Reviewer 1 Report

Summary:

The authors explain their experimental set up for evaluating the EMI-NL instrument - an instrument designed to go on thee DaQi 02 satellite to measure traces gases in both the nadir and limb profile. They use a laboratory set-up to measure NO₂, using known concentrations in a cylinder to assess their accuracy of their instrument. They find their instrument has errors between 3-8% depending on the experiment. They also find larger inconsistencies with different light sources. 

General Comments:

This is generally a good paper that is well written and clear. The science presented here is well described and they appear to have employed a sound method for analysing the instrument. I believe this paper can contribute to the scientific knowledge in the area with a few improvements that address the comments below. 

Abstract:

The abstract doesn't mention the inconsistencies mentioned in the results, they should be included briefly here as well.

Method:

Although the method is sound, it would be useful to explain certain parameters are used. Why do you choose the concentrations of NO₂? Are they representative of the range you would expect to detect from the satellite?

Results:

Do you expect the changes of performance between these concentrations to be linear? If you had more data points (ie. more NO₂ concentrations) do you expect it to impact results?

The introductory paragraph on the SNR is a bit vague. It would be good to elaborate on the impacts of this metric, in particular what it means for a detection limit. 

Do you know how these results compare to other satellite instrument tests? In particular, TROPOMI, which is a comparable satellite. (I don't know if this data is available)

Conclusions

The conclusion is a little limited. You reiterate your results but it needs more explanation about what this means in the broader picture. What are the impacts of these results? Are you just showing how the method can work? and if so, how could it be improved to reduce errors? Or is the purpose of this paper to show if the EMI-NL is adequate, and if this is the case, can you show that the results presented are within a scientifically acceptable range? Are the errors/inconsistencies presented here within a range that is acceptable for the satellite data?

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

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Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors well addressed the raised questions