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Evalua&on of the IRGASON Integrated CO2/H2O Gas Analyzer and Sonic Anemometer Steven P Oncley1, Thomas W Horst1, Edward Swiatek2, Ivan Bogoev2 1NaAonal Center for Atmospheric Research/Earth Observing Laboratory 2Campbell ScienAfic, Inc.
Air Flow Distor,on Evalua,on
Laboratory Evalua,on
Scalar Flux Measurement Evalua,on
Results -‐ IRGASON had more temperature driO than LI-‐7500 -‐ IRGASON had large offset (This IRGASON was replaced due to a faulty component, but this lab test of the new sensor was not repeated.)
Results -‐ VerAcal velocity (w) agrees quite well (variance difference <1%), especially for flow from up to +/-‐100 degrees from the front -‐ Horizontal velocity components (u,v) have larger errors: v severely
changed for wind direcAons beyond 80 degrees from front -‐ FricAon velocity (u*) differences of +/-‐15% observed even for
“good” wind direcAons
Method Apply 4 calibraAon gases from tanks to sensor at different temperatures.
Method Operate IRGASON side-‐by-‐side with reference CSAT3 sonic anemometer in the field. Over 500 hours of data with wind speed >2 m/s during 2012 were used. Check variaAon of mean, variance, and turbulence staAsAcs (u* and TKE) with wind direcAon (flow orientaAon with respect to the sensor head).
Conclusions -‐ IRGASON scalar (Tc, H2O, CO2) measurements similar
quality to LI-‐7500. (Tc is derived from speed of sound.) -‐ No spaAal separaAon correcAon needed -‐ Momentum flux measurement significantly compromised
Background Physical separaAon between measurements of verAcal velocity and H2O or CO2 systemaAcally reduces their calculated fluxes and must be corrected. The IRGASON addresses this problem by colocaAng these measurements, but could introduce errors in the velocity measurements. IRGASON data are available at up to 100 samples/s using 5W total of power.
Method Operate IRGASON in the field side-‐by-‐side with CSAT3 sonic anemometer plus LI-‐7500 open-‐path IRGA and krypton hygrometer. Field check calibraAon versus aspirated hygrometer for H2O and Picarro closed-‐path analyzer for CO2. Results -‐ Heat fluxes agree within 3% overall -‐ Both IRGAs must be cleaned! – significant driO in means seen when not done (more in LI-‐7500) -‐ A gain difference is seen between IRGANSON and LI-‐7500 H2O and CO2 fluctuaAon measurements, which explains much of the differences in the fluxes, but is not consistent with the variaAon of means with respect to the aspirated hygrometer and Picarro references -‐ Remaining difference in fluxes is consistent with under-‐correcAon
of LI-‐7500 fluxes due to spaAal separaAon -‐ AOer WPL correcAon for air density fluctuaAons, IRGASON fluxes
are reasonable (CO2 uptake during the day and respiraAon at night)
ICDC9 P194 Beijing, China
Example of nighnme fluxes: The correlaAon coefficient between w and CO2 is 30% lower from the LI-‐7500, presumably due to path separaAon. Our model of this separaAon predicts only a 4% effect, so even corrected fluxes would be underesAmated.
u StaAsAcs v StaAsAcs w/Tc StaAsAcs
mean
varia
nce
flux
CO2 density changes due to changing temperature and to changing CO2 mixing raAo. AOer removing the air density change, fluxes are more realisAc from the IRGASON, with CO2 uptake during the day. This implies that our LI-‐7500 was not well calibrated.
IRGASON (center), LI-‐7500 and krypton with CSAT3 (leO), and reference CSAT3 (right). Only wind direcAons not blocked by adjacent sensors were analyzed.
mean
varia
nce
flux
Tc StaAsAcs H2O StaAsAcs CO2 StaAsAcs
dir CSAT3 (deg)
Norm
alize
d Re
sidua
ls, (%
)−3
0−2
0−1
00
1020
30
−90 −60 −30 0 30 60 90 120 150
spd_IRGASON = 1.02 spd_CSAT3 + 0.09 +/− 0.054 m/s
−30
−20
−10
010
2030
dir CSAT3 (deg)
dir_
IRG
ASO
N −
dir_
CSAT
3 (d
eg)
−4−2
02
46
−90 −60 −30 0 30 60 90 120 150
dir_IRGASON − dir_CSAT3 vs dir_CSAT3
−4−2
02
46
dir CSAT3 (deg)
Norm
alize
d Re
sidua
ls, (%
)−4
0−3
0−2
0−1
00
1020
−90 −60 −30 0 30 60 90 120 150
u’u’_IRGASON = 1.05 u’u’_CSAT3 +/− 0.069 (m/s)^2
−40
−30
−20
−10
010
20
dir CSAT3 (deg)
Norm
alize
d Re
sidua
ls, (%
)−4
0−3
0−2
0−1
00
1020
−90 −60 −30 0 30 60 90 120 150
v’v’_IRGASON = 1.18 v’v’_CSAT3 +/− 0.117 (m/s)^2
−40
−30
−20
−10
010
20
dir CSAT3 (deg)
Norm
alize
d Re
sidua
ls, (%
)−3
0−2
0−1
00
1020
30
−90 −60 −30 0 30 60 90 120 150
w’w’_IRGASON = 1 w’w’_CSAT3 +/− 0.014 (m/s)^2
−30
−20
−10
010
2030
dir CSAT3 (deg)
Norm
alize
d Re
sidua
ls, (%
)−3
0−2
0−1
00
1020
30
−90 −60 −30 0 30 60 90 120 150
u*_IRGASON = 0.96 u*_CSAT3 +/− 0.031 m/s
−30
−20
−10
010
2030
dir CSAT3 (deg)
Norm
alize
d Re
sidua
ls, (%
)−3
0−2
0−1
00
1020
30
−90 −60 −30 0 30 60 90 120 150
TKE_IRGASON = 1.1 TKE_CSAT3 +/− 0.049 (m/s)^2
−30
−20
−10
010
2030
dir CSAT3 (deg)
Resid
uals,
(m/s
deg
C)−0
.03
−0.0
2−0
.01
0.0
0.01
0.02
0.03
0.04
−90 −60 −30 0 30 60 90 120 150
w’tc’_IRGASON = 0.99 w’tc’_CSAT3 +/− 0.009 m/s degC
−0.0
3−0
.02
−0.0
10.
00.
010.
020.
030.
04
dir CSAT3 (deg)
Norm
alize
d Re
sidua
ls, (%
)−3
0−2
0−1
00
1020
30
−90 −60 −30 0 30 60 90 120 150
tc’tc’_IRGASON = 1.02 tc’tc’_CSAT3 +/− 0.042 (degC)^2
−30
−20
−10
010
2030