The operational cloud retrieval algorithms from TROPOMI on board Sentinel-5 Precursor

Loyola, Diego G.; Gimeno García, Sebastián; Lutz, Ronny; Argyrouli, Athina; Romahn, Fabian; Spurr, Robert J. D.; Pedergnana, Mattia; Doicu, Adrian; Molina García, Víctor; Schüssler, Olena

doi:https://doi.org/10.5194/amt-11-409-2018

Articles | Volume 11, issue 1

https://doi.org/10.5194/amt-11-409-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

TROPOMI on Sentinel-5 Precursor: data products and...

https://doi.org/10.5194/amt-11-409-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 11, issue 1

Research article

|

18 Jan 2018

Research article |

| 18 Jan 2018

The operational cloud retrieval algorithms from TROPOMI on board Sentinel-5 Precursor

Diego G. Loyola, Sebastián Gimeno García, Ronny Lutz, Athina Argyrouli, Fabian Romahn, Robert J. D. Spurr, Mattia Pedergnana, Adrian Doicu, Víctor Molina García, and Olena Schüssler

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Final revised paper (published on 18 Jan 2018)
Preprint (discussion started on 15 May 2017)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'review', Anonymous Referee #2, 30 Jun 2017
- AC1: 'Reply to Referee #2', Diego Loyola, 07 Aug 2017
RC2: 'Review of amt-2017-128', Anonymous Referee #1, 30 Jun 2017
- AC2: 'Reply to Referee #1', Diego Loyola, 07 Aug 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Diego Loyola on behalf of the Authors (30 Sep 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (06 Oct 2017) by Joanna Joiner

RR by Anonymous Referee #2 (20 Oct 2017)

Suggestions for revision or reasons for rejection

Review of the revised manuscript by Loyola et al.

I think that the authors did not adequately address, at least, two comments which are important for evaluation of the algorithm error budget.

1. The authors state that the GB model was tested against the full RGB OCRA model and they found “only a small mean bias of 0.07” in the retrieved cloud fractions. No figure that illustrates the cloud fraction differences is provided. The cloud product is intended for the use in trace gas retrievals. For this purpose, the low cloud fraction range is most important. The mean bias of 0.07 is not small for low cloud fractions; it is quite large. The authors should compare cloud fractions from RGB and GB in more details and provide corresponding illustration. For example, they should look at the dependence of the mean bias on the RGB cloud fraction. The GB model may appear not to be appropriate for TROPOMI. Moreover, the red channel (675-775 nm) is available in TROPOMI; that is why the implementation of the RGB model has no problem for TROPOMI.

2. The authors removed the unsupported statement that “the use of water or ice properties has a relatively small impact on the O2 A-band spectral region”. However, they ignored my suggestion to compare the simulated TOA radiances and provide an estimate of cloud pressure errors due to the use of a single scattering phase function for water clouds. The authors answered “Mie theory is not sufficient to describe the scattering from ice crystals”. This is true. However the radiative transfer simulations do not necessarily require the Mie theory. The simulations do need a scattering phase function. Scattering phase function for ice clouds are available, e.g. at http://www.ssec.wisc.edu/∼baum/Cirrus/IceCloudModels.html.

I recommend the manuscript for publication after the authors address these comments.

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RR by Anonymous Referee #3 (23 Oct 2017)

ED: Publish subject to minor revisions (review by editor) (23 Oct 2017) by Joanna Joiner

AR by Diego Loyola on behalf of the Authors (02 Nov 2017) Author's response Manuscript

ED: Publish as is (05 Nov 2017) by Joanna Joiner

AR by Diego Loyola on behalf of the Authors (14 Nov 2017)

Short summary

In this paper we present the operational cloud retrieval algorithms for the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5 Precursor (S5P) mission: OCRA (Optical Cloud Recognition Algorithm) retrieves the cloud fraction using measurements in the UV–VIS spectral regions, and ROCINN (Retrieval of Cloud Information using Neural Networks) retrieves the cloud top height and optical thickness using measurements in and around the oxygen A-band in the NIR.