A simple retrieval of ground albedo and vegetation absorptance from MODIS satellite data for parameterisation of global Land-Surface Models

摘要

The task of parameterising global Land-Surface Models (LSMs) is rendered difficult by both the limited number of parameters that can be retrieved from eddy-covariance fluxes and the requirement for some physical processes to be modelled in a spatially explicit manner. Fortunately, some of the important biophysical parameters influencing energy exchange can be usefully constrained by satellite measurements of surface reflectance. In this study, we retrieve ground (soil) albedo and vegetation absorptance from the Moderate Resolution Imaging Spectroradiometer (MODIS) 1-arcdegree albedo product. This information is used to parameterise a revised global simulation of carbon, water and energy exchange at the land-surface. The new biophysical parameters produce significant modifications (5-30%) to predicted net radiation and sensible heat exchange, particularly for the northern sub-tropics and the boreal and northern tundra zones. We infer systematic differences in vegetation absorptance between 5 plant functional types (broadleaf forest, needleleaf forest, C grass, C grass and shrubland). The dispersion in values is fairly moderate within any given plant functional type (PFT), suggesting that a small number of PFTs is sufficient for setting albedo parameters within a global LSM.