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

[Kevin Wolz]

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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