[Reddyproc-users] Constraining Gap Filling to Certain "Epochs"

[Ladislav Šigut]

Hello Kevin,
I would say that the main problem is with setting the Reco sensitivity (E0 parameter). It needs quite long interval to produce robust results. Now this value should be constant throughout the dataset (Reichstein et al., 2005). Thus if you have it computed (with whole dataset), you could theoretically feed it to the function that is computing Rref. This should theoretically require shorter periods and you would apply it to individual short periods ("epochs"). If I remember, feeding E0 is possible but it really depends on the design of the code if it will anyway let you work with it. I have never tried it myself.
I hope it helps.
Best wishes

Ladislav Šigut, M.Sc.
Department of Matter and Energy Fluxes
Global Change Research Institute CAS
Bělidla 986/4a, CZ-60300 Brno, Czech Republic
+420 511 192 286 / +420 606 641 694
www.czechglobe.cz<http://www.czechglobe.cz/>

From: reddyproc-users-bounces at lists.r-forge.r-project.org [mailto:reddyproc-users-bounces at lists.r-forge.r-project.org] On Behalf Of Kevin Wolz
Sent: Saturday, February 4, 2017 6:07 PM
To: reddyproc-users at lists.r-forge.r-project.org
Cc: Kevin Wolz <wolz1 at illinois.edu>
Subject: [Reddyproc-users] Constraining Gap Filling to Certain "Epochs"

Hello REddyProc Users,
I have an interesting, non-standard requirement for gap filling that I am trying to determine how to implement. Our eddy covariance tower is placed in a grass field that is cut for hay approximately once per month. These cutting events create dramatic, instantaneous shifts in NEE that last for several weeks as the grass recovers. You can see our NEE data for 2016 is the attached file, including the raw data supplied to REddyProcWeb and the gap-filled data after each confidence level of gap filling. Overall, the gap filling works quite well. However, it is clear that the dramatic shifts in the state of the ecosystem that take place during grass cutting do create issues with the algorithm because the algorithm is "blind" to these events. You can see the result of this in the second attachment, which is zoomed in and identifies erroneous gaps that have been filled with data from the wrong "epoch" of pre- versus "post" grass cutting.

While I understand that this type of point shift in NEE is not very common in natural ecosystems, there are now more and more eddy covariance towers in managed ecosystems that do experience management-induced point shifts in NEE. I am wondering if it is somehow possible to deal with this situation using the REddyProcWeb tool. My first thought was to only supply the tool with data from one "epoch" at a time, but the minimum amount of data to pass to the tool is 3 months, whereas some of these "epochs" only last a few weeks. Consequently, I wonder if it might be necessary to consider another possible column input to the tool, similar to the u* season column, that is used to restrict the search windows of the gap filling algorithm to within a certain "epoch".

I would very much appreciate any advice on how to make this possible!

Thank you!
Kevin
--
Kevin Wolz
PhD Candidate, DeLucia Lab
University of Illinois at Urbana-Champaign
Phone: (708) 476-9929
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