A GLOBAL SURFACE REFLECTIVITY DATA SET FOR THE 2.2-2.35 MU-M REGION

The lack of surface reflectivity data in the near-infrared region and the need of this information for an on-going project on remote soundin g of atmospheric pollution motivated a search for a scientific, yet pr actical approach to creating a global data set of surface reflectivity with seasonality at 2.2-2.35 mu m region. Since the surface reflectiv ity varies significantly with the type of unvegetated ground and the e xtent of surface vegetation coverage, attempts were first made to dete rmine the surface reflectivity of each of the major 'components' of th e Earth's surface in the spectrum region of interest. The Landsat TM b and 7 data were used to derive the reflectivity values for those compo nents. Furthermore, the global Leaf Area Index (LAI) data set from the International Satellite Land Surface Climatology Project (ISLSCP) was used to calculate the seasonal variation of the fraction of vegetatio n coverage of any given surface areas. A global map of reflectivity in the 2.3 mu m region is then derived by taking a weighted average of t he reflectivity values of several basic components of the underlying s urface. The weight of each characteristic surface component comes from its fractional area. A brief description is presented on how to calcu late the fraction of vegetation coverage characterized by the green Le af Area Fraction (LAF) from widely available Normalized Difference Veg etation Index (NDVI) data sets. Also presented is the comparison of th e derived surface reflectivity by this approach with independently cal culated reflectivity values from the Landsat data for some selected ar eas. The overall methodology can be extended to achieve a higher-resol ution mapping when the required data sets become available.