Eddy Covariance QC Workshop

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AmeriFlux Intercomparison system
Hollinger, D., Loescher, H., Evans, R., and
members of AmeriFlux
Eddy - Covariance  QC -Workshop
Castle Thurnau, November 15 17, 2002
CARBOEUROPE /CARBOEUROFLUX  afo-2000 / VERTIKO
DEKLIM / EVA_GRIPS
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Objectives

• Reduce uncertainty in estimates of CO2, H and LE
  exchange within and among AmeriFlux sites and
  among different networks,
• deliver better science through intercalibration
  and team-wide QA/QC,
• software processing of standardized flux data
  files Gold Files
• comparison of flux system response to a roving
  standard

This system does not determine the suitability of
the site for making eddy covariance
measurements. It is up to researchers at each
site to insure that fetch, energy balance,
spectral corrections, and other issues are fully
addressed.
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AmeriFlux Portable System

• Temperature
• OMEGA 4-wire PT-100, OM5-IP4-N100C signal
  conditioner, Campbell 21X Datalogger (0.05 oC)
• 3 primary standards, H20 (ice/boiling
  point), Gallium m.p.,
• 10 secondary standards, aluminum block in
  water bath,
• Vapor Pressure
• LiCOR LI-610 dew pt generator, General Eastern
  dew point mirror (0.2 oC)
• CO2
• LiCOR Li-6262 analyzer
• (temperature, pressure, and flow controlled) 4
  CMDL CO2 stds, 4 secondary stds (0.4 umol CO2
  mol-1)
• PPFD
• LiCor Model LI-190SA , Campbell 21X ( 5)

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AmeriFlux Portable System (cont)

• Net Radiation
• REBS Model Q7.1 with ventilator (5, wind
  correction 0.25), Campbell 21X
• Windspeed
• Applied Technologies Model SAT1-3K Sonic
  anemometer (0.01 m s-1)
• Flux system
• Temperature flow (6.5 l min-1) controlled
  LI-6262, HDPE tubing, rotary vane pump, LiCor
  pressure sensor, DAQBOOK (16 bit, 0-5V) data
  acquisition system, 4-di-pole Butterworth filter,
  30 Hz corner frequency,10 Hz data rate

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• Calibration
• IRGA - WMO gas stds.
• Temperature
• Net Radiation
• PPFD
• Intercomparisons
• Fluxes H, LE, CO2
• Met T, Rn, PPFD
• 41 sites, 10 countries

Temp aspirators
Net Radiometers Quantum sensors
ATI vs. Gill
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Comparison Methodology

• AmeriFlux System transported to site, setup
  adjacent to site system
• Systems operated for 3-5 days
• Comparisons made for met sensors fluxes on
  half-hourly data
• Slope, intercept, r2 (RMA)
• Report to site
• Changes made

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Environmental Variables

• Summary
• Rn little bias
• PPFD low bias outliers
• Tair outliers

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Fluxes

• Summary
• No bias
• Outliers depend on equipment in use
• Not consistent spectral corrections

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Recommendations based on AmeriFlux calibration
results to date

• Ventilators for net radiometers
• Calibrated PT-100 in an aspirated shield, signal
  conditioner for Tair
• WMO CO2 standards for all sites (NIGEC bulk
  purchase)
• Analysis of gold files prior to visit

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