Column Integrated Water Vapor and Aerosol Load Characterization with the New ZEN-R52 Radiometer

Round 1

Reviewer 1 Report

The work presented in this paper is very important and fits the agenda of this journal. The ZEN-R52 radiometer is a very ambitious move forward and the specifications and results are presented for the for the first time. A robust work has been performed in order to validate retrievals and the methods are described in a clear way. Hence, I suggest accepting the manuscript for publishing after minor changes.

 

My main concern is the use of Libradtran for retrieving water vapor at 940 nm. Default libraries in the package are to be used up to 850 nm (where detailed cross section for gases are included) and the suggestion is to use line by line model at longer wavelengths.  Emde et al., 2016, provide an overview of the package and they explain that in paragraphs 4.2 and 4.3. My own experience is the attached figure, which shows MODTRAN and Libradtran calculations in that spectral region for 0.5 and 3.5 cm of PWV. This shows that libradtran is not sufficiently “sensitive” at PWV changes at this bandwidth. The method presented seems to provide retrievals with an uncertainty in acceptable limits. Thus I would not suggest to recalculate all LUT with different package, but at least, I expect some discussion on this matter.I guess the wide FWHM could play some role on the sensitivity also.

 

 

L58 I think that radiosondes, which actually measure water vapor in situ while ascending is the most trustworthy measurement. It lacks in temporal and spatial resolution, but this should be the reference measurement. Thus, I suggest to restate this sentence in order not to underestimate this type of measurement.

 

L91, It should be restated , because it seems that PWV and AOD are inversion products, which is not true.

 

L139 There is some literature about steady biases for aeronet PWV, I suggest to add some discussion and references here.

 

2.2.1 First Paragraph: It is important to explicitly state the software and hardware improvements of R52. Also, it should be clearly stated that the measurements are of incoming irradiance at the zenithial column.

 

L173, Since there is a 5% calibration uncertainty, the total uncertainty of any retrieval cannot be lower than that.  Hence, this should be clear when uncertainties of retrievals are calculated at other sections.

 

L216 Is there any estimation or references for the uncertainty of FTIR retrieval?

 

L234 It is not clear how the aerosol profiles used in model calculations are fitted to actual data. Also, does the aerosol profile used add some uncertainty?

 

L310. Does the selection of the midlatitude summer atmosphere affect the estimations of aerosol profiles?

L498 It is crucial to discuss the uncertainty budget of IWV. How AOD and instrumental uncertainties are propagated this product. Are the differences from the other retrievals explained by those errors?

 

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Reviewer 2 Report

This paper is in general well written.  In Section 1: Introduction, it needs more relevant references and provides sufficient background based on the related work of other researchers.

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Reviewer 3 Report

The manuscript "Column integrated water vapour and aerosol load characterization with the new ZEN-R52 radiometer" by Almansa et al. is a very well written paper and is very much suitable for publication in this journal. I have 2 minor comment:

1. Please include a section​/paragraph in the conclusion that talks about the limitations/disadvantages of ZenR52
2. Include some text to provide more information on how the band width for each spectral band is chosen, and how accurate they are?

I recommend this paper for publication in this journal.

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