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

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Presentation on theme: "Aircraft and tower eddy covariance flux measurements SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy) B. Gioli (IBIMET CNR, Italy)"— Presentation transcript:

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

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

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

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

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

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

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 hypothesis 1. ~Flat terrain 2. Homogeneity 3. Stationarity 4. '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: CO 2 & H 2 O (fast) measurements Open Path IRGA (Infra Red Gas Analyzer) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

14 Isola di Pianosa Installations Norunda, Svezia 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 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) Vaccari et al 2003

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

18 Complicating factors: 2. footprint estimation where the measured flux comes from ? SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy) 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)

19 Complicating factors: 3. CO2 flux partioning SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy) 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) NEE = GPP – Reco NEE = Net Ecosystem Exchange GPP = Gross Primary Productivity Reco = Ecosystem respiration

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

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

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

23 (relative) wind measurement differential & static pressures Dynamic pressure 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 Aircraft motion measurement Sistema alternativo (NOAA, IATA): Attitude GPS + accelerometri Attitude 3D GPS a 4 antenne (10 Hz) accelerometri (50 Hz) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

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

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

28 The products 3D wind + scalar (T, H 2 O, CO 2 ) fast measurements (50 Hz) (eddy covariance tecnique) Surface fluxes along flight track (u *, H, LE, fCO 2 ) SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy) Flux transect over NL (Gioli et al 2006)

29 Tower data – 30 min continuous data Aircraft data – ‘Spatial’ Fluxes Data characteristics 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 H LE G H? LE ? G CONTROLTREATMENT (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 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 ? Can we observe change in energy partioning by eddy covariance & remote sensing ? SSOS- Summer School on Optical Sampling (7-13 July 2011, Trento, Italy)

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

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

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


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