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Appendix C. EasyFlux
®
DL CR6KH20
C-36
TABLE C-22. Data Fields in the Flux_Notes Output Table
Data Field Name
Units
Description
Data Field
Included
shfp_cal_fail_x_1_1
none
Result of TRUE indicates HFP01SC
returned an invalid number or the
calibrated sensitivity was not within
80%-105% of the original sensitivity
If HFP01SC
used
process_time
ms
Average processing time for each scan
Always
process_time_Max
Ms
Maximum processing time for a scan
Always
buff_depth_Max
Number
Maximum number of records stored in
the buffer
Always
C.4.5 Program Sequence of Measurement and Corrections
The following are the main correction procedures and algorithms implemented
in the program. The oxygen correction is unique to the KH20; see Appendix
Equations and Algorithms of Water Vapor Density and Water Flux in KH20
(p. D-1)
. For the other corrections, more details about
the theory and implementation may be found in the appendices of the
EasyFlux
DL CR6OP
manual.
1.
Despike and filter 10 Hz data using sonic and KH20 diagnostic codes.
2.
Coordinate rotations with an option to use the double rotation method
(Tanner and Thurtell 1969), or planar fit method (Wilczak et al.
2001).
3.
Lag CO
2
and H
2
O measurements against sonic wind measurements for
maximization of CO
2
and H
2
O fluxes (Horst and Lenschow 2009,
Foken et al. 2012), with additional constraints to ensure lags are
physically possible.
4.
Apply oxygen correction to covariances with water density from the
KH20. (See Appendix
Equations and Algorithms of Water Vapor
Density and Water Flux in KH20 Eddy-Covariance Systems
.)
5.
Frequency corrections using commonly used cospectra (Moore 1986,
van Dijk 2002a, Moncrieff et al. 1997) and transfer functions of block
averaging (Kaimal et al. 1989), line/volume averaging (Moore 1986,
Moncrieff et al. 1997, Foken et al. 2012, van Dijk 2002a), time
constants (Montgomery 1947, Shapland et al. 2014, Geankoplis
1993), and sensor separation (Horst and Lenschow 2009, Foken et al.
2012).
6.
A modified SND correction (Schotanus et al. 1983) to derive sensible
heat flux from sonic sensible heat flux following the implementation
as outlined in van Dijk 2002b. Additionally, fully corrected real
sensible heat flux computed from fine-wire thermometry may be
provided.
7.
Correction for air density changes using WPL equations (Webb et al.
1980).