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aircraft and tower eddy covariance flux measurements

aircraft and tower eddy covariance flux measurements. B. Gioli (IBIMET CNR, Italy). SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy). Layout. 1. TOWER FLUX MEASUREMENTS 2. AIRCRAFT FLUX MEASUREMENTS 3. FLUX MANIPULATION EXPERIMENT.

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aircraft and tower eddy covariance flux measurements

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  1. aircraft and tower eddy covariance flux measurements B. Gioli (IBIMET CNR, Italy) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  2. Layout 1. TOWER FLUX MEASUREMENTS 2. AIRCRAFT FLUX MEASUREMENTS 3. FLUX MANIPULATION EXPERIMENT SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  3. 1. TOWER FLUX MEASUREMENTS • - principles of the eddy covariance micrometeorological tecnique; • - how to use turbulence to measure fluxes • tecnique assumptions and limitations SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  4. wind & turbulence SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  5. wind & turbulence air motion is 3D and made by 'fluctuations' SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  6. surface exchange +CO2 -CO2 downdraft (w-) updraft (w+) CO2 sink surface SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  7. surface exchange (one eddy) Flux associated to one eddy = c1w1 + c2w2 c2, w2 c1, w1 downdraft (w-) updraft (w+) CO2 sink surface SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  8. +CO2 -CO2 downdraft (w-) updraft (w+) CO2 sink surface surface exchange (general) Fluctuations of vertical wind and scalars c’ = c - c w’ = w - w

  9. Fluxes from a typical EC tower (at typically 30 min resolution) Net Ecosystem Exchange Sensible heat flux Latent heat flux = evapotransp. Momentum flux = friction velocity SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  10. NEE H, LE SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  11. EC hypothesis1. ~Flat terrain 2. Homogeneity3. Stationarity4. 'enough' turbulence SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  12. Technology: 3D wind (fast) measurement SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  13. Technology: CO2 & H2O (fast) measurements Open Path IRGA (Infra Red Gas Analyzer) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  14. Installations Norunda, Svezia Isola di Pianosa SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  15. FluxNet SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  16. Vaccari et al 2003 Complicating factors: 1. frequency response:do we measure ALL the flux by eddy covariance ? Rn = SW↓ +LW ↓ - SW↑ -LW↑ (net radiation) H + LE + G = Rn H: sensible heat flux (EC measured) LE: latent heat flux = evapotranspiration (EC measured) G = soil heat flux (measured) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  17. Complicating factors: 1. frequency response:do we measure ALL the flux by eddy covariance ? cospectra of CO2 and W low freq. ~ minutes high freq. ~ parts of a second SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  18. Complicating factors: 2. footprint estimationwhere the measured flux comes from ? • Footprint area = area contributing to the observed flux • Footprint area extends upwind the observation point, and is a function of: • Atmospheric stability • Wind speed and direction • Surface roughness • Footprint area is estimated trough models (analytic, stochastic, lagrangian back-trajectory) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  19. Complicating factors: 3. CO2 flux partioning NEE = GPP – Reco NEE = Net Ecosystem Exchange GPP = Gross Primary Productivity Reco = Ecosystem respiration • approaches exist to partition NEE into GPP and Reco, based on night time fluxes to dirve a respiration response to temperature and soil water content (Reichstein et al 2003) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  20. 2. AIRCRAFT FLUX MEASUREMENTS SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  21. Net Radiation PAR Radiation Attitude GPS Novatel GPS GPS Electronics Switch BOX IRGA Pressure Sphere T Fast Response T Low Response Surface T Dew Point T Videocamera Sky Arrow ERA

  22. Mobile Flux Platform (MFP) Measurement of 3D winds @ 50 Hz CO2, H2O, T fast sensors SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  23. Dynamic pressure differential & static pressures (relative) wind measurement SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  24. SkyArrow ERA: wind measurement principle SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  25. Attitude 3D GPS a 4 antenne (10 Hz) accelerometri (50 Hz) Aircraft motion measurement Sistema alternativo (NOAA, IATA): Attitude GPS + accelerometri SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  26. GPS Position Velocity 10Hz Ground GPS Position Velocity Attitude 50Hz Actual 3D wind 50Hz Attitude 10Hz Actual 3D wind retrieval Pressures 50 Hz Attitude GPS Accelerometers 50Hz SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  27. IRGA Gas Analyzer Pressure Ports System calibration SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  28. The products 3D wind + scalar (T, H2O, CO2) fast measurements (50 Hz) (eddy covariance tecnique) Surface fluxes along flight track (u*, H, LE, fCO2) Flux transect over NL (Gioli et al 2006) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  29. Data characteristics Tower data – 30 min continuous data Aircraft data – ‘Spatial’ Fluxes SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  30. Footprint concept & aircraft fluxes SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  31. Validation of aircraft flux measurements SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  32. Vellinga et al 2010 Regional C-budgets SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  33. Validation of RS-based surface schemes at regional scale SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  34. Some conclusions part 1 & 2 • eddy covariance widely used to measure surface fluxes across biomes, at high temporal resolution • limitations arise from potential flux loss, & not perfect conditions (orography, inhomogeneities, low turbulence at night...) • EC measures NEE, while GPP needs to be retrieved trough Reco estimation at nigh time (difficult...) • EC can be succefully applied from aircraft platform and regional scale fluxes measured SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  35. 3. FLUX MANIPULATION EXPERIMENT SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  36. Surface energy balance Rn = SW↓ +LW ↓ - SW↑ -LW↑ (net radiation) Rn = H + LE + G H: sensible heat flux (EC measured) LE: latent heat flux = evapotranspiration (EC measured) G = soil heat flux (measured) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  37. Study area

  38. FLUX MANIPULATION EXPERIMENT Rn LE H? H LE ? G G CONTROL TREATMENT (antitranspirant) Measurements: H, LE, G (eddy towers) Ts (IR camera on aircraft) VIS-NIR (ground + aircraft) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  39. Can we observe change in energy partioning by eddy covariance & remote sensing ? can we observe a decrease in LE ? can we observe an increase in H ? can we observe an increase in Ts ? how is VIS-NIR reflectance affected ? how is photosynthesis affected ? SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  40. Measuring Ts with thermal remote sensing Stefan–Boltzmann law Wien's displacement law • IR camera detects 7.5 – 12 micron • emissivity needed to estimate Ts SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

  41. Using Ts to assess surface energy balance H = Cp (Ts – Ta) / Rtot Rtot = Rsto + Rnsto (total resistance) Rsto = resistance for water to be transpired trough stomata Rnsto = other resistance (aerodynamic) Eddy covariance can be used to measure both resistances: H, LE  Penman Monteith equation  rc (stomatal resistance) u, u*  aerodynamic resistance

  42. why is surface energy balance important ? Feedbacks in the coupled land-atmosphere system van Heerwaarden et al, 2009 at plot scale: atmosphere  surface (plot) at larger scale: atmosphere  surface (region) positive feedback negative feedback

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