Radiative Transfer in Shrub Savanna Sites in Niger: Preliminary Results fromHapex-Sahel. Part 1: Modelling Surface Reflectance Using a Geometric-Optical Approach

摘要

To use optical remote sensing to monitor land surface-climate interactions overlarge areas, algorithms must be developed to relate multispectral measurements to key variables controlling the exchange of matter (water, carbon dioxide) and energy between the land surface and the atmosphere. An areal-proportion model of the multispectral reflectance of shrub savanna, composed of scattered shrubs with a grass, forest, or soil understory, predicted the reflectance of two 0.5 sq km sites as the area-weighted average of the shrub and understory or 'background' reflectances. A submodel predicted the reflectance of the shrub crown as a function of the foliage reflectance and amount of plant material within the crown, and the background reflectance scattered or transmitted through canopy gaps (referred to as a soil-plant 'spectral interaction' term). One may be able to combine these two models to estimate both the fraction of vegetation cover and interception of PAR by green vegetation in a shrub savanna.