Uncertainty analysis of eddy covariance CO<sub>2</sub> flux measurements for different EC tower distances using an extended two-tower approach

Post, H.; Hendricks Franssen, H. J.; Graf, A.; Schmidt, M.; Vereecken, H.

doi:https://doi.org/10.5194/bg-12-1205-2015

Articles | Volume 12, issue 4

https://doi.org/10.5194/bg-12-1205-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

9th International Carbon Dioxide Conference (ICDC9) (ESD/ACP/AMT/BG...

https://doi.org/10.5194/bg-12-1205-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 4

Research article

|

25 Feb 2015

Research article |

| 25 Feb 2015

Uncertainty analysis of eddy covariance CO₂ flux measurements for different EC tower distances using an extended two-tower approach

H. Post, H. J. Hendricks Franssen, A. Graf, M. Schmidt, and H. Vereecken

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Final revised paper (published on 25 Feb 2015)
Preprint (discussion started on 06 Aug 2014)

Interactive discussion

Status: closed

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

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RC C5042: 'referee comment on Post et al.', Anonymous Referee #2, 10 Sep 2014
- AC C5500: 'Reply to interactive comment by anonymous referee #2 (RC C5042)', Hanna Post, 28 Sep 2014
RC C5257: 'Review of BG manuscript', Ankur Desai, 21 Sep 2014

Peer-review completion

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

AR by Hanna Post on behalf of the Authors (31 Oct 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (03 Dec 2014) by Anna Michalak

RR by Ankur Desai (10 Dec 2014)

RR by Anonymous Referee #2 (10 Jan 2015)

Suggestions for revision or reasons for rejection

Review on the manuscript by H.Post et al. titled ‘Uncertainty analysis of eddy covariance CO2 flux measurements for different EC tower distances using an extended two-tower approach’, re-submitted in a revised version for publication to Biogeosciences in Nov 2014.

The presented manuscript has been significantly improved compared to the previous version, and most of the referee’s comments have been implemented well. The text is clearly structured and well written, and besides for a few minor passages it is of adequate length. While all scientific glitches have been straightened out, the one major issue that remains is the relevance/applicability of this approach. This is a nice study overall, but it could have been strengthened with some more convincing arguments why one would prefer this approach over the one based on raw data statistics (used as a reference herein). However, overall I recommend accepting this manuscript for publication after considering the few minor issues listed below.

Detailed comments

i) the new approach to determine footprint overlap is a good solution for this metric; however, the current concept (lines 344ff) of using the minimum footprint value for each grid cell is a bit complicated to follow. It’s certainly not incorrect, but in my opinion it would be a bit more intuitive if you used the maximum value instead – in this case, for total overlap you would still end up with a sum of 1, while for totally independent footprints that sum would be 2.

ii) Some sections in the introduction are still a bit lengthy. E.g., it’s a good thing to explain the sign convention you used for uptake/release of CO2 by the ecosystem (though this doesn’t need to be provided in the intro), but there’s no need to explain that ER dominates fluxes at nighttime. In the discussion section, you sometime refer to statements already given further above (which is OK), but you repeat these statements (which should be avoided).

iii) I noticed that at least one reference (Foken et al., 2004) is used in the text, but not given in the reference list. So please have a close look again at your citations (also the format used it the text is not always ‘clean’). Btw, Foken et al. (2004) would be the better reference for their quality flagging scheme, since some aspects given in the original paper by Foken and Wichura (1996) have been revised.

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ED: Publish subject to technical corrections (29 Jan 2015) by Anna Michalak

AR by Hanna Post on behalf of the Authors (06 Feb 2015) Manuscript

Short summary

This study introduces an extension of the classical two-tower approach for uncertainty estimation of measured net CO2 fluxes (NEE). Because land surface properties cannot be assumed identical at two eddy covariance towers, a correction for systematic flux differences is proposed to be added to the classical weather filter. With this extension, the overestimation of NEE uncertainty due to systematic flux differences (which are assumed to increase with tower distance) can considerably be reduced.