An earth-gridded SSM/I data set for cryospheric studies and global change monitoring

The National Snow and Ice Data Center (NSIDC) has distributed DMSP Special Sensor Microwave Imager (SSM/I) brightness temperature grids for the Polar Regions on CD-ROM since 1987. In order to expand this product to include all potential snow covered regions, the area of coverage is now global. The format for the global SSM/I data set is the Equal Area SSM/I Earth Grid (EASE-Grid) developed at NSIDC. The EASE-Grid has been selected as the format for the NASA/NOAA Pathfinder Program Level 3 Products which include both SSM/I and SMMR (Scanning Multichannel Microwave Radiometer) data (1978-1987). Providing both data sets in the EASE-Grid will result in a 15 year time-series of satellite passive microwave data in a common format. The extent and variability of seasonal snow cover is recognized to be an important parameter in climate and hydrologic systems and trends in snow cover serve as an indicator of global climatic changes. Passive microwave data from satellites afford the possibility to monitor temporal and spatial variations in snow cover on the global scale, avoiding the problems of cloud cover and darkness. NSIDC is developing the capability to produce daily snow products from the DMSP-SSM/I satellite with a spatial resolution of 25 km. In order to provide a standard environment in which to validate SSM/I algorithm output, it is necessary to assemble baseline data sets using other, more direct, methods of measurement. NSIDC has compiled a validation data set of surface station measurements for the northern hemisphere with specific focus on the United States, Canada, and the former Soviet Union. Digital image subtraction is applied to compare the surface station and satellite measurements.