Comparing the Seasonal Dynamics in Vegetation Function, Biophysical and Spectral Properties, Using Orbital Observations at Globally Distributed Flux Sites

Abstract:

Climate change and anthropogenic activities have significantly altered agricultural and forest productivity by imposing combinations of multiple stresses. Consistent observations at appropriate temporal, spectral and spatial resolution are required to capture the dynamics in vegetation function to be able to detect the transient responses to stress factors, as the ecosystems cycle through phenology and respond to variable environmental conditions. Currently, observations from multiple sources (e.g., field, airborne and orbital) are required to monitor vegetation function and canopy bio-physical and spectral properties at the relevant time steps, and at a spatial resolution suitable for forestry and agricultural management. We will present the analysis of reflectance time series for monitoring the seasonal dynamics in canopy photosynthesis for a range of vegetation types at globally distributed flux sites, in preparation for work with large scale spectroscopy time series, which will be available from the forthcoming Surface Biology and Geology (SBG/NASA) global hyperspectral mission. We utilized NASA’s EO-1 Hyperion, DESIS (ISS) and the Harmonized Landsat Sentinel (HLS) archives, to generate dense time series for a set of eddy covariance sites, representing a broad range of vegetation functional types. Field measurements and eddy covariance data were used to characterize canopy photosynthetic function, derive canopy chlorophyll estimates and calculate gross primary productivity (GPP). Using the reflectance spectra, for each flux site we implemented the integrated bio-physical and radiative transfer model ‘Soil Canopy Observation, Photochemistry and Energy fluxes’ (SCOPE), to obtain vegetation biophysical traits. We tested spectroscopic, statistical and modeling approaches for estimating ecosystem productivity (GPP) and canopy chlorophyll content. Comparisons among the seasonal dynamics in vegetation function at the flux sites, and the associated canopy bio-physical and spectral properties revealed differences, indicative of the factors limiting vegetation function. The work contributes to extend the timeline for future SBG products, and to demonstrate their value for science, and supports research within NASAs SBG, MuSLI and Terrestrial Ecology programs.