in measurements 10 hz data of 3d wind speed t sonic h 2 o co 2 pressure out fluxes 0.000556 hz data...
DESCRIPTION
Theoretical assumptions (D. Baldocchi, J. Finnigan et al.) Conservation of mass, i.e. input+output+storage=0 Reynolds’ decomposition Averaging done over long enough period (accommodate larger eddies), and over short enough periods (not be affected by diurnal patterns)TRANSCRIPT
Methods for processing eddy covariance Methods for processing eddy covariance data: (re-)inventing the wheel. data: (re-)inventing the wheel.
Asko NoormetsAsko Noormets
IN
Measurements10 Hz data of • 3D wind speed• Tsonic
• H2O
• CO2
• Pressure
OUT
Fluxes0.000556 Hz data of • Fc (carbon flux)• LE (water flux)• Hs (sensible heat flux)
Proc
essi
ng
Theoretical assumptions (D. Baldocchi, J. Finnigan et al.)
• Conservation of mass, i.e. input+output+storage=0
• Reynolds’ decomposition• Averaging done over long enough period (accommodate larger
eddies), and over short enough periods (not be affected by diurnal patterns)
uuu
Flux = change in mixing ratio (I)+ advection (II)+ flux divergence (vertical, lateral & longitudinal) (III)+ biological source/sink strength (IV)
Ideally:I=0, II=0, III=0
In reality:I II III 0Measured covariance = true covariance + sensor bias
),,( zyxSyF
xF
zF
tcw
tcv
tcu
tc
dtcd
B
yxz
I II III IV
'' cwF
Processing steps (D. Billesbach)
1. Replace spikes (>6) with the moving window mean. 2. Correct sonic temperature (CSAT) for humidity & pressure (IRGA). 3. Calculate deviations of each measurement from a 30-minute block average. 4. Calculate rotation angles using the block means (vmean = 0; wmean = 0).
5. Calculate all possible covariance pairs and rotated covariances. 6. Calculate density correction terms for LE and Fc (WPL). 7. Calculate the frequency correction factor for the sonic anemometer. 8. Calculate the frequency correction factor for the sonic anemometer and IRGA
combination. 9. Adjust the WPL H term by the sonic frequency correction factor. 10. Adjust Fc and the WPL LE terms by the sonic-IRGA frequency correction factor. 11. Calculate final LE and Fc, that are rotated, adjusted for density and frequency bias.
******
*
Data processing
`
Coordinate rotation
u
vw
Rotation:
0''
0
0
wv
w
v
Fc+wpl+storage, July - w/o rotation
- rotated
s i t e=mhw
f c_ sum
- 1. 2
- 1. 1
- 1. 0
- 0. 9
- 0. 8
- 0. 7
- 0. 6
- 0. 5
- 0. 4
- 0. 3
- 0. 2
- 0. 1
0. 0
0. 1
0. 2
0. 3
0. 4
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
s i t e=mr p
f c_ sum
- 1. 5
- 1. 4
- 1. 3
- 1. 2
- 1. 1
- 1. 0
- 0. 9
- 0. 8
- 0. 7
- 0. 6
- 0. 5
- 0. 4
- 0. 3
- 0. 2
- 0. 1
0. 0
0. 1
0. 2
0. 3
0. 4
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0s i t e=pb
f c_ sum
- 0. 8
- 0. 7
- 0. 6
- 0. 5
- 0. 4
- 0. 3
- 0. 2
- 0. 1
0. 0
0. 1
0. 2
0. 3
0. 4
0. 5
0. 6
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0s i t e=yhw
f c_ sum
- 0. 8
- 0. 7
- 0. 6
- 0. 5
- 0. 4
- 0. 3
- 0. 2
- 0. 1
0. 0
0. 1
0. 2
0. 3
0. 4
0. 5
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
s i t e=yr p
f c_ sum
- 0. 9
- 0. 8
- 0. 7
- 0. 6
- 0. 5
- 0. 4
- 0. 3
- 0. 2
- 0. 1
0. 0
0. 1
0. 2
0. 3
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
Fc+wpl+storage, November - w/o rotation
- rotated
s i t e=mhw
f c_ sum
- 0. 30
- 0. 28
- 0. 26
- 0. 24
- 0. 22
- 0. 20
- 0. 18
- 0. 16
- 0. 14
- 0. 12
- 0. 10
- 0. 08
- 0. 06
- 0. 04
- 0. 02
0. 00
0. 02
0. 04
0. 06
0. 08
0. 10
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
s i t e=mr p
f c_ sum
- 0. 5
- 0. 4
- 0. 3
- 0. 2
- 0. 1
0. 0
0. 1
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0s i t e=pb
f c_ sum
- 0. 20- 0. 18- 0. 16- 0. 14- 0. 12- 0. 10- 0. 08- 0. 06- 0. 04- 0. 02
0. 000. 020. 040. 060. 080. 100. 120. 140. 160. 180. 200. 220. 240. 260. 280. 300. 32
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0s i t e=yhw
f c_ sum
- 0. 14- 0. 12- 0. 10
- 0. 08- 0. 06- 0. 04- 0. 02
0. 000. 02
0. 040. 060. 080. 100. 12
0. 140. 160. 180. 200. 220. 24
0. 260. 28
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
s i t e=yr p
f c_ sum
- 0. 23- 0. 22- 0. 21- 0. 20- 0. 19- 0. 18- 0. 17- 0. 16- 0. 15- 0. 14- 0. 13- 0. 12- 0. 11- 0. 10- 0. 09- 0. 08- 0. 07- 0. 06- 0. 05- 0. 04- 0. 03- 0. 02- 0. 01
0. 000. 010. 020. 03
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
Respiration, with () and without () coordinate rotation
s i t e=mhw
r espi r
0. 10
0. 11
0. 12
0. 13
0. 14
0. 15
0. 16
0. 17
0. 18
0. 19
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
si t e=mhw
r espi r
0. 0120. 0130. 0140. 0150. 0160. 0170. 0180. 0190. 0200. 0210. 0220. 0230. 0240. 0250. 0260. 0270. 0280. 0290. 0300. 0310. 0320. 0330. 034
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
July
November
Rotation effect (rerel):
- uncorrected flux - wpl-corrected - wpl- & storage-
corrected, gapfilled
mont h=7
r ot eff 4
- 1. 1
- 1. 0
- 0. 9
- 0. 8
- 0. 7
- 0. 6
- 0. 5
- 0. 4
- 0. 3
- 0. 2
- 0. 1
0. 0
0. 1
0. 2
0. 3
0. 4
0. 5
0. 6
0. 7
0. 8
0. 9
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
mont h=11
r ot eff 4
- 3
- 2
- 1
0
1
2
3
t i me
0. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 0
rotated
rawrotated
FcFc-Fc
relre
July
November
AQ parameters, MHW
- w/o rotation - rotated
0
1
2
3
4 6 8 10Month
Pmax
00.0010.0020.0030.004
4 6 8 10Month
Alph
a
-0.3
-0.2
-0.1
0
4 6 8 10Month
Respira
tion
Comparison of three methodsFc, July 21-26, 2002
C-1-rot. vs. C-2-roty = 0.6413x - 0.1867
R2 = 0.4917
-2
-1
0
1
2
-2 -1 0 1 2
SAS-1-rot. vs. C-2-roty = 0.855x - 0.1399
R2 = 0.6819
-2
-1
0
1
2
-2 -1 0 1 2
SAS-1-rot. vs. C-1-rot.y = 0.943x - 0.0164
R2 = 0.6933
-2
-1
0
1
2
-2 -1 0 1 2
Comparison of three methods, July 21-26, 2002
-2
-1
0
1
2
7/21 7/22 7/23 7/24 7/25 7/26 7/27
2 rotations, C+1 rotation, C+1 rotation, SAS
Comparison of three methodsLE, July 21-26, 2002
C-1-rot. vs. C-2-rot.y = 0.6856x + 28.778
R2 = 0.7051
0
100
200
300
400
500
600
0 100 200 300 400 500 600
SAS-1-rot. vs. C-2-rot.y = 0.7248x + 23.361
R2 = 0.728
0
100
200
300
400
500
600
0 100 200 300 400 500 600
SAS-1-rot. vs. C-1-rot.y = 0.9477x + 2.8615
R2 = 0.7988
0
100
200
300
400
500
600
0 100 200 300 400 500 600
Uncertainties remain
Flux = change in concentration (I)+ advection (II)+ flux divergence (vertical, lateral & longitudinal) (III)+ biological source/sink strength (IV)
Ideally:I=0, II=0, III=0
In reality:I II III 0Measured covariance = true covariance + sensor bias
(high- and low-pass filtering spectral correction factors 1.04-1.36 for Fc and LE)
),,( zyxSyF
xF
zF
tcw
tcv
tcu
tc
dtcd
B
yxz
For more comprehensive overview:
Finnigan JJ, Clement R, Malhi Y, Leuning R, Cleugh HA (2003) A re-evaluation of long-term flux measurement techniques - Part I: Averaging and coordinate rotation. Boundary-Layer Meteorology 107, 1-48.