Assessment of inputs to Land Surface Processes Models derived from hyperspectral multi-angular data

Computer Science – Performance

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Global Models of the Earth-Atmosphere System describe the role of the terrestrial biosphere using increasingly complex Land Surface Models (LSM). These models mimic the exchange of energy, water and carbon between the land and the atmosphere, with emphasis on the role of terrestrial vegetation. Literature shows a clear trend towards fully interactive LSM-s, i.e. accounting for the dynamic response of vegetation to weather and climate. The latter may not be limited to biomass accumulation and address slower changes in vegetation type and composition. Improving the performance of such models require addressing two broad questions: 1. Can we measure vegetation properties with the accuracy required by model sensitivity? 2. How do we measure vegetation properties over the grid size of Global Models and are we able to incorporate the inherent spatial heterogeneity of terrestrial vegetation? The role of terrestrial vegetation in the land-atmosphere exchanges of energy, water and carbon is determined by properties, such as albedo, fAPAR, LAI and chlorophyll, related to spectro-directional radiances in the range 0.4 μm-14 μm. These variables and their spatial patterns can, therefore, be determined with accurate observations of spectrodirectional radiances at selected view-angles and wavelengths. The paper summarizes results of several field experiments and airborne campaigns in Spain, France and Germany dedicated to these scientific objectives during the period 1998-2000. Examples are presented of the use of multiangular hyperspectral measurements to determine LAI, fAPAR, chlorophyll and heat fluxes with both field and airborne measurements. Particular attention is dedicated to illustrate the need for multiangular observations in the entire spectral range 0.4μm-14μm. See [1] and other papers in these proceedings for more information on background activities. Multi-angular hyperspectral observations provide measurements of variables directly related to the exchange of energy, water and carbon: A. Evaporative fraction (see paper by Jia et al. [2] in this volume) energy B. Water Index (see papers by Leone et al. [3] and by Moreno et al. [4] in this volume) water C. Chlorophyll (see paper by Leone et al. [3] and by Moreno et al. [4] in this volume) carbon In all cases multiangular observations are necessary, as demonstrated in previous papers in these proceedings. When estimating hemispherical variables such as albedo and emissivity, the angular distribution of radiance must be properly sampled. When estimating biophysical variables, such chlorophyll and water content from spectral measurements, the ambiguity of observed radiance due to angular anisotropy has to be corrected using multiangular measurements.

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