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Scaling GPP at Flux Tower Sites in the Context of EOS/MODIS Validation

Scaling GPP at Flux Tower Sites in the Context of EOS/MODIS Validation. David P. Turner Oregon State University. Validating MODIS Terrestrial Ecology Products with Satellite and In-situ Measurements Warren Cohen USDA Forest Service David Turner Oregon State University Tom Gower

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Scaling GPP at Flux Tower Sites in the Context of EOS/MODIS Validation

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  1. Scaling GPP at Flux Tower Sites in the Context of EOS/MODIS Validation David P. Turner Oregon State University

  2. Validating MODIS Terrestrial Ecology Products with Satellite and In-situ Measurements Warren Cohen USDA Forest Service David Turner Oregon State University Tom Gower University of Wisconsin Peter Reich University of Minnesota Steve Running University of Montana

  3. BigFoot Objectives Develop and validate data layers (25 km2) for land cover, leaf area index (LAI), and net primary production (NPP) at high spatial resolution (25 m) at sites representing the major biomes Use these data layers for validation of MODIS land cover, LAI and NPP products Study scaling issues related to monitoring of global NPP

  4. HARV Capturing seasonality With ETM+ is important to both land cover and LAI mapping HARV Leaf-off Leaf-on KONZ April July September

  5. Field-Based Sampling Design 100 25m2 plots 80 in a nested spatial series 20 plots broadly distributed Plot measurements Vegetation cover LAI, fPAR Aboveground biomass Aboveground productivity Belowground productivity

  6. GPP =  (NEE – Re) For daylight period GPP = gross primary production (gC m-2 d-1) NEE = net ecosystem exchange (half hourly) Re = ecosystem respiration (half hourly)

  7. MODIS GPP Product GPP (gC m-2 d-1) = PAR * fAPAR * g Where: PAR = from DAO climate model fAPAR= from MODIS reflectances g ( gC MJ-1) = GPP / APAR MODIS g from lookup table Spatial Resolution is 1 km Temporal Res. is 8-day mean

  8. 27 July 99 AGRO (29 July 99) 98 % accurate (cross validation) LAI P vs. O r^2 = 0.72

  9. * * Data courtesy of S. Wofsy and Ameriflux

  10. * * Data courtesy of S. Wofsy and Ameriflux

  11. * Data courtesy of D. Bremmer, A. Knapp, J. Ham

  12. * * Data courtesy of T. Meyers and FLUXNET

  13. NPP and GPP at the Northern Boreas Site (units are gC m-2 yr-1) Old Black Spruce (1994) ANPP (measured ) 148 BNPP (estimated) 135 TNPP 285 GPP (flux tower) ~800 NPP/GPP 0.36 TNPP (measured) 285 Plant Respiration (scaled) 880 GPP 1165 NPP/GPP 0.25

  14. NPP and GPP at the Konza Site (units are gC m-2 yr-1) tallgrass prairie (1997) ANPP (measured ) 128 BNPP (estimated) 256 TNPP 384 GPP (flux tower) 1453 NPP/GPP 0.26 TNPP (simulated) 731 GPP (simulated) 1349 NPP/GPP (simulated) 0.54

  15. * Konza Prairie false color composite TM imagery * Images courtesy of Konza LTER web site

  16. NPP and GPP at the Bondville Site (units are gC m-2 yr-1) corn (1999) soybean (1999) ANPP (measured ) 874 478 BNPP (estimated) 97 36 TNPP 971 514 GPP (flux tower) 1453 (1999) NPP/GPP 0.67 TNPP (simulated) 953 527 GPP (simulated) 1606 896 NPP/GPP 0.59 0.60

  17. * * Derived from tower PAR data courtesy of S. Wofsy and Ameriflux

  18. Conclusions Still lots to be done reconciling tower-based GPP and the sum of measured NPP and scaled plant respiration At some tower sites, spatial heterogeneity matters in linking tower NEE to field measurements and modeling A scaling approach using high resolution remote sensing and NPP models permits indirect linkage of flux tower measurements to MODIS GPP products at the 1 km spatial resolution and 8 day temporal resolution

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