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 sounding of atmospheric pollution motivated a search for a scientific, yet practical approach to creating a global data set of surface reflectivity with seasonality at 2.2-2.35 mu m region. Since the surface reflectivity varies significantly with the type of unvegetated ground and the extent of surface vegetation coverage, attempts were first made to determine the surface reflectivity of each of the major 'components' of the Earth's surface in the spectrum region of interest. The Landsat TM band 7 data were used to derive the reflectivity values for those components. 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 vegetation 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 the reflectivity values of several basic components of the underlying surface. The weight of each characteristic surface component comes from its fractional area. A brief description is presented on how to calculate the fraction of vegetation coverage characterized by the green Leaf Area Fraction (LAF) from widely available Normalized Difference Vegetation Index (NDVI) data sets. Also presented is the comparison of the derived surface reflectivity by this approach with independently calculated reflectivity values from the Landsat data for some selected areas. The overall methodology can be extended to achieve a higher-resolution mapping when the required data sets become available.