Evaluating land surface parameters in the Biosphere-Atmosphere Transfer Scheme using remotely sensed data sets

Remotely sensed data sets were used to evaluate the spatial/temporal specif ication of albedo (alpha), roughness length (Z(0)), and green leaf area ind ex (L-g) in the Biosphere-Atmosphere Transfer Scheme (BATS). These paramete rs were evaluated for 1988 and 1993 in the Upper Mississippi River Basin (U MRB) using data from the International Satellite Land Surface Climatology P roject Initiative 1 (ISLSCP 1) and by applying the ISLSCP 1 algorithms to h igh spatial resolution satellite data (Pathfinder advanced very high resolu tion radiometer (AVHRR) land(PAL)). ISLSCP 1 L-g was more variable spatiall y than BATS, particularly in midsummer months. ISLSCP 1 alpha was generally lower than BATS at BATS and ISLSCP 1 generally showed small spatial variab ility in alpha for a given cover type. ISLSCP 1 Z(0) were up to 100% larger than BATS. Spatial/temporal variability in ISLSCP 1 and BATS Z(0) was prim arily restricted to the spring. Comparisons between the ISLSCP 1 and PAL da ta indicated substantial differences in estimates of L-g and Z(0) because o f differences in the transformation of the vegetation index to L-g and grid cell heterogeneity. PAL L-g and Z(0) were extremely variable spatially. La rge differences between years in the PAL Lg were found, particularly in cli mate-affected regions. The remotely sensed data indicate that improved para meterizations in BATS are needed to account for spatial variability in L-g and Z(0), as well as interannual variability in L-g. However, the compariso ns also demonstrate that assumptions inherent in remote sensing algorithms and the impact of these on parameter estimates must be carefully examined.