Mapping surface‐cover parameters using aggregation rules and remotely sensed cover classes
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AbstractA coupled model, which combines the Biosphere—Atmosphere Transfer Scheme (BATS) with an advanced atmospheric boundary‐layer model, is used to validate hypothetical aggregation rules for BATS‐specific surfacecover parameters. the model is initialized and tested with observations from the Anglo—Brazilian Amazonian Climate Observational Study and is used to simulate surface fluxes for rain forest and pasture mixes at a site near Manaus in Brazil. the aggregation rules are shown to estimate parameters which give area‐average surface fluxes similar to those calculated, with explicit representation of forest and pasture patches for a range of meteorological and surface conditions relevant to this site, but the agreement deteriorates somewhat when there are large patchto‐patch differences in soil moisture. the aggregation rules, validated as above, are then applied to a remotely sensed 1 km land‐cover data set to obtain grid‐average values of BATS vegetation parameters for 2.8° x 2.8° and 1° x 1° grids within the conterminous United States. There are significant differences in key vegetation parameters (aerodynamic roughness length, albedo, leaf‐area index, and stomatal resistance) when aggregate parameters are compared with parameters for the single, dominant cover within the grid. However, the surface energy fluxes calculated by stand‐alone BATS with the 2‐year forcing data from the International Satellite Land Surface Climatology Pogramme CD‐ROM are reasonably similar using aggregate‐vegetation parameters and dominant‐cover parameters, but there are some significant differences, particularly in the western USA.
