HR: 14:25h
AN: B43F-04    [Abstracts]
TI: Linking the Seasonal Variation of Vegetation Indices to Tower Flux Measurements in an Oak-Savanna Ecosystem in California: Comparing the Performance of Ground Based Sensors to Remotely Sensed Products from MODIS, AVIRIS and IKONOS.
AU: * Falk, M
EM: mfalk@nature.berkeley.edu
AF: Departement of Environmetal Science, Policy and Management, University of California, 107 Mulford Hall #3110, Berkeley, CA 947203110
AU: Baldocchi, D D
EM: baldocchi@nature.berkeley.edu
AF: Departement of Environmetal Science, Policy and Management, University of California, 107 Mulford Hall #3110, Berkeley, CA 947203110
AU: Mercado, I R
EM: ilse@berkeley.edu
AF: Department of Civil and Environmental Engineering, University of California, 760 Davis Hall, Berkeley, CA 947201710
AU: Ma, S
EM: sma@nature.berkeley
AF: Departement of Environmetal Science, Policy and Management, University of California, 107 Mulford Hall #3110, Berkeley, CA 947203110
AU: Hehn, T
EM: thehn@nature.berkeley.edu
AF: Departement of Environmetal Science, Policy and Management, University of California, 107 Mulford Hall #3110, Berkeley, CA 947203110
AB: Across the globe, there are now over 200 FLUXNET sites sampling tower fluxes over many vegetation types. However the spatial resolution of the tower sites is limited and additional information is needed to provide the Global Change Research community with an accurate way to identify and quantify carbon sources and sinks on regional, continental and global scales. Remote sensing is a major tool capable of providing information about the dynamics of the terrestrial biosphere with continuous spatial and temporal coverage on a global scale. For this purpose vegetation indices are chosen specifically to enhance the contribution of vegetation properties to surface reflectances. Remote sensing products generally produce information on GPP (or net primary productivity, NPP), in terms of a light use efficiency (ε) and the amount of absorbed visible sunlight (fPAR). Linking remote sensing with FLUXNET sites is crucial in providing reliable estimates of the magnitude and dynamics of the terrestrial carbon budget. An important issue is the spatial mismatch between the NASA Moderate Resolution Imaging Spectrometer (MODIS) and the footprint of tower observations. In this study we have conducted seasonal observations of VI's using three different ground based sensors: a high resolution spectrometer on a weekly basis, and a spectrally-selective light emitting diode spectrometer and a broadband radiometer providing continuous measurements for a highly dynamic oak-savanna ecosystem. We investigate seasonal changes in ε, drought induced changes in carbon uptake (NEE) and their link to different VI's like the Normalized Differential Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and the Photochemical Reaction Index (PRI). Using a combination of spatially coarse MODIS data with high resolution snapshots from IKONOS and AVIRIS platforms together with the ground based spectral observations, we expand the tower site results to regional scale. We find that NDVI is an overall poor correlator with NEE for the dynamic grassland with pronounced winter time photosythesis and extensive drought stress. EVI and especially PRI provide better linkage of spectral reflectance data to the actual photosynthetic activity of the grassland ecosystem.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0452 Instruments and techniques
DE: 0480 Remote sensing
SC: Biogeosciences [B]
MN: Fall Meeting 2005