Performance of the FMI cosine error correction method for the Brewer spectral UV measurements

Lakkala, Kaisa; Arola, Antti; Gröbner, Julian; León-Luis, Sergio Fabian; Redondas, Alberto; Kazadzis, Stelios; Karppinen, Tomi; Karhu, Juha Matti; Egli, Luca; Heikkilä, Anu; Koskela, Tapani; Serrano, Antonio; Vilaplana, José Manuel

doi:https://doi.org/10.5194/amt-11-5167-2018

Articles | Volume 11, issue 9

https://doi.org/10.5194/amt-11-5167-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-11-5167-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 11, issue 9

Research article

|

11 Sep 2018

Research article |

| 11 Sep 2018

Performance of the FMI cosine error correction method for the Brewer spectral UV measurements

Kaisa Lakkala, Antti Arola, Julian Gröbner, Sergio Fabian León-Luis, Alberto Redondas, Stelios Kazadzis, Tomi Karppinen, Juha Matti Karhu, Luca Egli, Anu Heikkilä, Tapani Koskela, Antonio Serrano, and José Manuel Vilaplana

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Final revised paper (published on 11 Sep 2018)
Preprint (discussion started on 20 Dec 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Reviewer commnets', Anonymous Referee #1, 11 Jan 2018
- AC1: 'Response to comments of Referee #1', Kaisa Lakkala, 30 Apr 2018
RC2: 'Artifacts of the cosine error correction method should be addressed before publication', Anonymous Referee #2, 13 Jan 2018
- AC2: 'Response to comments of Referee #2', Kaisa Lakkala, 30 Apr 2018

Peer-review completion

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

AR by Kaisa Lakkala on behalf of the Authors (08 May 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 May 2018) by Andreas Hofzumahaus

RR by Anonymous Referee #1 (26 May 2018)

Suggestions for revision or reasons for rejection

The revised manuscript has been substantially improved with respect to the original. The authors have responded adequately to the comments of both reviewers, and they have revised the text accordingly. There are still a couple of points that should be addressed before the manuscript is published.

Lookup tables:
As far as it concerns the cloud optical depth, the lookup tables have been constructed assuming increments of 5 in COD. This might be also a source of uncertainty particularly for COD between 0 and 5, where the largest effect on the direct component occurs. For COD=5 the direct component is almost zero while for COD=0 there is no effect. I think that the interpolation between these two extreme cases will lead to significant uncertainties. I suggest to the authors to consider in the future to update the LUT with more frequent increments of COD between 0 and 5. Maybe this can be mentioned in the Discussions section.

Last paragraph of section 3:
The discussion using the papers by Webb and Kylling is a bit confusing because the diffuse actinic flux is mentioned for the first time without providing the context of the discussion. The discussion of the Appendix helps but since it will not be included in the paper, the readers will have difficulties to understand this paragraph. I am not suggesting to include the appendix, but to rephrase the paragraph in order to convey clearly the message to the reader. To my understanding, the main point is that the assumption of isotropy leads to uncertainties that may explain part of the difference between the QASUME and the cosine corrected Brewer data.
By the way, the constancy of the ratio diffuse actinic to diffuse global irradiance of about 1.75 is published in Kazadzis et al 2004 (their Fig. 1 and Table 2). https://www.atmos-chem-phys.net/4/2215/2004/

Comment General 2 of Reviewer #2:
The wavelength structure seen in figure 5 cannot be attributed to systematic biases between model and measurements unless this refers to systematic structures due to differences in spectral resolution. I am suspecting (a) spectral resolution problems which may arise from the imperfect knowledge of the slit functions that were used in the convolution and (b) random spectral features in the measured spectra. Structures consistent for all instruments at a specific wavelength could possibly be explained by (a) above, while those appearing solely for a specific instrument to (b).

Technical comments:
I suggest to move the text starting at P2, l 34 “Even if the above …..was obvious.” before the text starting at P2, l28 “The Finish meteorological …. measured data.” These sentences refer to methods other than the FMI’s so it is better to be placed before the FMI’s method.

P5, L11: Delete “previous dark”
P6, L13: Delete “dark room”
P7, L2: Delete “global cosine correction”
P8, L7: Replace “As the azimuth is integrated over all directions, i.e. 2π” with “As C(θ,λ) is assumed independent of azimuth angle”
P12, L6: Replace “impact” with “contribution”
Figures 7 and 8: Please pair the panels appropriately (side by side) so that each pair corresponds to one instrument.

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RR by Anonymous Referee #3 (28 May 2018)

ED: Publish subject to minor revisions (review by editor) (04 Jun 2018) by Andreas Hofzumahaus

AR by Kaisa Lakkala on behalf of the Authors (14 Jun 2018) Author's response Manuscript

ED: Publish as is (19 Jun 2018) by Andreas Hofzumahaus

AR by Kaisa Lakkala on behalf of the Authors (29 Jun 2018) Author's response Manuscript

Short summary

The performance of the cosine error correction method for correcting spectral UV measurements of the Brewer spectroradiometer was studied. The correction depends on the sky radiation distribution, which can change during one spectral scan. The results showed that the correction varied between 4 and 14 %, and that the relative differences between the reference and the Brewer diminished by 10 %. The method is applicable to other instruments as long as the required input parameters are available.