Satellite Mapping of Solar Ultraviolet Radiation at the Earth’s Surface

It is often assumed that any anthropogenic trend in stratospheric ozone abundance must inevitably bring about an ecologically significant inverse trend in surface solar ultraviolet radiation (UVR) at the earth’s surface. In reality, the spatial and temporal distribution of surface UVR is governed primarily by variability in stratospheric ozone abundance, cloud opacity, and solar elevation, and is also influenced by tropospheric ozone, aerosol, and surface albedo. In many parts of the world the natural variability in cloud cover alone can result in a large enough interannual variability in surface UVR that the ecological significance of an ozone-related UVR trend may be questionable (Lubin and Jensen, 1995). The best way to address the issue of anthropogenic trends versus natural variability in surface UVR is to make continuous in situ measurements of UVR flux at as many locations as possible using modern spectral radiometric equipment. As discussed in this volume, many nations have established such UVR monitoring programs within the past five years, and by the end of the century the scientific community may have a robust database with which to place ozone depletion in proper environmental perspective. In the meantime, we can begin to understand the global climatology of surface UVR by using various satellite data as input to radiative transfer models. Even with a network of spectroradiometers, satellite data can be useful to generalize their measurements to larger geographic areas, and to interpolate between surface measuring stations.