Gap Filling Comparison Workshop, September 18-20, 2006, Jena, Germany
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Transcript of Gap Filling Comparison Workshop, September 18-20, 2006, Jena, Germany
Gap Filling Comparison Workshop, September 18-20, 2006, Jena, Germany
Corinna RebmannOlaf Kolle
Max-Planck-Institute for BiogeochemistryJena, Germany
Eddy covariance measurements and their shortcomings for the
determination of the net ecosystem exchange of carbon dioxide
Outline
• Introduction of measurement site and advection experiment
• Reasons for data gapsSpecial features of open path analyser
• Consequences for final flux data
• Summary
Measurement Site:
Wetzstein, Thuringia, Germany,
flux measurements established end of 2001
main towertower C tower B
tower D
tower A
measuring heights: Main tower: 30.0mTower C: 29.4m
ADVEX’06 (April 11– June 19, 2006)flux measurements for , H, E, CO2
CO2, wind and temperature profiles
The ADVEX Experiment
Advection experiment CarboEurope-IP:4 towers around the main tower:A, B, C, D: profiles of [CO2], T, u‘, v‘, w‘, T‘,tower B with CO2-fluxes below canopy,tower C and main tower with CO2-fluxes above canopy
60m
Why care about advection?
Eddy covariance theory is derived from tracer conservation equation with many simplifications which are only valid under homogeneous conditions
Data gaps are due to
• Maintenance interruptions, power failures, ice coating
• Instrumental problems• Non-turbulent conditions• Unfavoured wind directions (tower effects,
heterogeneous terrain)• Precipitation, fog events (open path
analyser)• high wind speeds
Wetzstein, main towerdata gaps (closed-path analyser)
Jan 1 – Aug 24, 2006
00:00
12:00
00:00
Tim
e
1.1. 1.3. 1.5. 1.7.
caused by maintainance, power failure, ice coating
1.9% gaps
00:00
12:00
00:00
1.1. 1.3. 1.5. 1.7.
after pre-selection ( high-frequency data)
3.5% gaps
00:00
12:00
00:00
Tim
e
1.1. 1.3. 1.5. 1.7.
Date
after stationarity test 1 ( diff >50%)
25.9% gaps
00:00
12:00
00:00
1.1. 1.3. 1.5. 1.7.
Date
after stationarity test 2 ( 30%<diff<50%)
42.1% gaps
data available
no data
Wetzstein, main tower and tower CApr 11 – Jun 19, 2006
data gaps caused by maintenance, power failures etc.
-100
-80
-60
-40
-20
0
20
40
60
FC
O(µ
mol
ms
)2
-2-1
0.0
1.0
2.0
3.0
4.0
prec
ipita
tion
(mm
)
15.4. 22.4. 29.4.1.5. 8.5. 15.5. 22.5. 29.5. 1.6. 8.6. 15.6.
Date
FCO2 TM
FCO2 TC
precip (mm)
Wetzstein, main tower and tower CApr 11 – Jun 19, 2006
data gaps caused by maintenance, power failures etc.
step Main tower (TM)
Tower C (TC)
1(maintenance etc)
3.6% 4.8%
2(after pre-selection)
3(after stationarity test 1)
Wetzstein, main tower and tower CApr 11 – Jun 19, 2006
time series of CO2-fluxes after pre-selection(eg Vickers & Mahrt 1997, JAOT14)
-40
-30
-20
-10
0
10
20
FC
O(µ
mol
ms
)2
-2-1
0.0
1.0
2.0
3.0
4.0
rain
(mm
)
15.4. 22.4. 29.4.1.5. 8.5. 15.5. 22.5. 29.5. 1.6. 8.6. 15.6.
Date
FCO2 TM
FCO2 TC
rain (mm)
Wetzstein, main tower and tower CApr 11 – Jun 19, 2006
data gaps after pre-selection
step Main tower (TM)
Tower C (TC)
1(maintenance etc)
3.6% 4.8%
2(after pre-selection)
4.5% 30.2%
3(after stationarity test 1)
30.2%
Wetzstein, main tower and tower C
which data are rejected in case of open path-analyser?
-40
-30
-20
-10
0
10
20
FC
O(µ
mol
ms
)2
-2-1
0.0
1.0
2.0
3.0
4.0
rain
(mm
)
1.5. 8.5. 15.5. 22.5. 29.5. 1.6. 8.6.
Date
FCO2 TM
FCO2 TC
rain (mm)
-40
-30
-20
-10
0
10
20
FC
O(µ
mol
ms
)2
-2-1
0.0
1.0
2.0
3.0
4.0
rain
(mm
)
1.5. 2.5. 3.5. 4.5. 5.5. 6.5. 7.5. 8.5. 9.5. 10.5. 11.5. 12.5. 13.5.
Date
FCO2 TM
FCO2 TC
rain (mm)
24 of 624 half-hours (3.8%) rejected
April 30 – May 12, 2006, dry period
Wetzstein, main tower and tower C
which data are rejected in case of open path-analyser?
-40
-30
-20
-10
0
10
20
FC
O(µ
mol
ms
)2
-2-1
0.0
1.0
2.0
3.0
4.0
rain
(mm
)
1.5. 8.5. 15.5. 22.5. 29.5. 1.6. 8.6.
Date
FCO2 TM
FCO2 TC
rain (mm)
-40
-30
-20
-10
0
10
20
FC
O(µ
mol
ms
)2
-2-1
0.0
1.0
2.0
3.0
4.0
rain
(mm
)
14.5. 15.5. 16.5. 17.5. 18.5. 19.5. 20.5. 21.5. 22.5. 23.5. 24.5. 25.5. 26.5. 27.5. 28.5.
Date
FCO2 TM
FCO2 TC
rain (mm)
263 of 630 half-hours (41.7%) rejected!!!
May 13 – 28, 2006, rainy period
Wetzstein, main tower and tower C Apr 11 – Jun 19, 2006
consequences for dependencies on meteorological variables
GGsatGPP
GsatGPPday R
RaF
RFaNEE
,
,Michalis-Menten-relationship:see Falge et al. 2001, AFM107
NEE: net ecosystem exchange (µmol CO2 m−2 s−1)
PPFD: photosynthetic photon flux density (µmol quantum m−2 s−1)
a: ecosystem quantum yield (µmol CO2) / (µmol quantum)
FGPP,sat: gross primary productivity at saturating light (µmol CO2 m−2 s−1)
Rday: ecosystem respiration during the day (µmol CO2 m−2 s−1)
-30
-20
-10
0
10
NE
E(µ
mo
lms
)-2
-1
0 200 400 600 800 1000 1200 1400 1600 1800 2000
PPFD (µmol m s )-2 -1
day-time NEE, TM
day-time NEE, TC TM TC
a 0.057 0.061
FGPP,sat 24.6 27.6
Rday 5.4 4.1
r2 0.66 0.58
Wetzstein, main tower and tower C Apr 11 – Jun 19, 2006
consequences for dependencies on meteorological variables
GGsatGPP
GsatGPPday R
RaF
RFaNEE
,
,Michalis-Menten-relationship:see Falge et al. 2001, AFM107
NEE: net ecosystem exchange (µmol CO2 m−2 s−1)
PPFD: photosynthetic photon flux density (µmol quantum m−2 s−1)
a: ecosystem quantum yield (µmol CO2) / (µmol quantum)
FGPP,sat: gross primary productivity at saturating light (µmol CO2 m−2 s−1)
Rday: ecosystem respiration during the day (µmol CO2 m−2 s−1)
-30
-20
-10
0
10
NE
E(µ
mol
ms
)-2
-1
0 200 400 600 800 1000 1200 1400 1600 1800 2000
PPFD (µmol m s )-2 -1
day-time NEE, TM, if CT av.
day-time NEE, TMTM TM,
TC avTC
a 0.057 0.063 0.061
FGPP,sat 24.6 23.2 27.6
Rday 5.4 5.1 4.1
r2 0.66 0.59 0.58
Wetzstein, main tower and tower C
time series of CO2-fluxes with stationarity tests
-40
-30
-20
-10
0
10
20
FC
O(µ
mo
lms
)2
-2-1
1.5. 3.5. 5.5. 7.5. 9.5. 11.5. 13.5. 15.5. 17.5. 19.5.
Date & Time
FCO2 TM
FCO2 TC
FCO2 TM if stat2
FCO2 TC if stat2
-30
-20
-10
0
10
20
FC
O(µ
mol
ms
)2
-2-1
0
100
200
300
400
500
600
700
800
900
1000
R(W
m)
G-2
9.5. 10.5. 10.5. 11.5. 11.5. 12.5. 12.5. 13.5. 13.5. 14.5. 14.5. 15.5.
Date
FCO2 TM
FCO2 TC
FCO2 TM if stat2
FCO2 TC if stat2
global radiation RG
May 8 – 14, 2006
Wetzstein, main tower and tower CApr 11 – Jun 19, 2006
When do instationaries occur?
0
5
10
15
num
ber
ofin
stat
ion
ary
dat
a(%
)
10 50 90 130
170
210
250
290
330
370
410
450
490
530
570
610
650
690
730
770
810
850
R (W m )G-2
TM
TC
Instationarities occur mainly atlow or zero radiation conditions
Wetzstein, main tower and tower CApr 11 – Jun 19, 2006data gaps summary
step Main tower (TM)
Tower C (TC)
1 3.6% 4.8%
2(after pre-selection)
4.5% 30.2%rainy, moist conditions
3(after stationarity test 1)
9.8% 33.2%
Low radiation conditions
Do we have perfect data now?
Are these data reliable as input for gap filling procedures?
Still missing:advective processesnight flux treatment
reliability check
HainichDrainage/advective fluxes
Data fromW. Kutsch
-20
-10
0
10
FC
O(µ
mo
lms
)2
-2-1 storage flux
turbulent flux
-10
-5
0
5
10
FC
O(µ
mol
ms
)2
-2-1 Horiz.Advection
running mean
0.0
1.0
qual
ityfla
gs
17.8. 18.8. 18.8. 19.8. 19.8. 20.8. 20.8.
Date & Time
physical/technical flag
stationarity flag
nighttime u* flag
12:00 12:00 12:00 12:00
Night-flux problem
• Weak turbulence• Instrumental problems, large footprints,
gravity waves• Turbulent flux is influenced by other
transport/storage processes→Site dependentsee eg: Lee, 1998
Aubinet et al, 2003, 2005Staebler and Fitzjarrald, 2004Feigenwinter et al, 2004
Night-flux corrections
Empirical:
Separate calm and turbulent periods, remove calm periods, fill the gap
u*-criterion mostly used
Aubinet et al. AER30, 2000
NEEnight versus u*
0.0
1.0
2.0
3.0
4.0
norm
aliz
ed
CO
-flu
x2
0
2
4
6
8
10
12
14
16
18
20
freq
uen
cy(%
)
0.0
250.
125
0.2
250.
325
0.4
250.
525
0.6
250.
725
0.8
250.
925
1.0
251.
125
1.2
251.
325
1.4
251.
525
1.6
251.
725
1.8
251.
925
u* (m s )-1
Wetzstein, n=7446
-40
-30
-20
-10
0
10
20
30
FC
O(µ
mol
ms
)2
-2-1
15.9. 17.9. 19.9. 21.9. 23.9. 25.9. 27.9. 29.9.
Date
WetzsteinNEE 2005, unrealistic high night-time fluxes
Wetzsteinwhen do high fluxes occur?
• u*>0.4m s-1• wind direction between 200° and 280° or 30° and 40°• neutral atmospheric conditions:
stability parameter: -0.0625<ζ<0.0625
(determined by M. Zeri)
→ turbulent upwind mixing from the valley
WetzsteinNEE 2005
after application of MZ criteria
-40
-30
-20
-10
0
10
20
30
FC
O(µ
mol
ms
)2
-2-1
15.9. 17.9. 19.9. 21.9. 23.9. 25.9. 27.9. 29.9.
Date
NEE MT, after MZ criteria
NEE MT, before MZ criteria
for 2005:72% data available58% data available
WetzsteinNEE 2005
after application of MZ criteria
0.0
1.0
2.0
3.0
4.0
norm
aliz
ed
CO
-flu
x2
0
2
4
6
8
10
12
14
16
18
20
freq
uen
cy(%
)
0.0
250.
125
0.2
250.
325
0.4
250.
525
0.6
250.
725
0.8
250.
925
1.0
251.
125
1.2
251.
325
1.4
251.
525
1.6
251.
725
1.8
251.
925
u* (m s )-1
Wetzstein, n=7446
0.0
1.0
2.0
3.0
4.0
norm
aliz
edC
O-f
lux
2
0
2
4
6
8
10
12
14
16
18
20
freq
uenc
y(%
)
0.02
50.
125
0.22
50.
325
0.42
50.
525
0.62
50.
725
0.82
50.
925
1.02
51.
125
1.22
51.
325
1.42
51.
525
1.62
51.
725
1.82
51.
925
u* (m s )-1
Wetzstein, n=4991
after selection criteria
Wetzsteinnight-time NEE 2005
after application of MZ criteria
-10
0
10
20
30
FC
O(µ
mo
lms
)2
-2-1
-20 -15 -10 -5 0 5 10 15 20 25 30
T (°C)air, 2m
NEE after pre-selection, stationary
NEE after pre-selection, stationary and MZ criteria
R10=3.9R10=3.0
WetzsteinNEE comparison during advection experiment
after application of MZ criteria
-30
-20
-10
0
10
20
FC
O(µ
mol
ms
)2
-2-1
11.5. 12.5. 13.5. 14.5. 15.5. 16.5. 17.5. 18.5. 19.5. 20.5. 21.5.
Date in 2006
MT, left after MZ criteria
MT, discarded with MZ criteria
TC
TS
SummaryAmount of data gaps strongly depending on:• site• type of quality check
(still no common agreement in CarboEurope-IP!)• type of analyser, weather pattern• threshold criteria for u*
(have to be objective, Gu et al. AFM128, 2005)
Derived dependencies on meteorological variables vary with data left after selection
→biased datasets
Reliability has to be tested against chamber and biometric measurements
Thanks for your attention!
Questions?