Comparative analysis of UV-B exposure between nimbus 7/TOMS satellite estimates and ground-based measurements

This study describes the patterns of variation in ultraviolet (UV) exposure across time and space, using two continental scale datasets on UV radiation, and conducts a comparative analysis of two sources of noontime UV-B exposure data across the continental U.S. One dataset was collected from 37 ground-based stations equipped with broadband UV-B-1 Pyranometers across North America whereas the other dataset was of synchronous satellite data collected from the Nimbus-7/TOMS sensor. Comparisons of these datasets confirmed agreement between the ground-based measurements and the TOMS satellite estimates with correlation coefficients of 0.87 and 0.95 for daily and monthly Ultraviolet Index (UV-I) time series (i.e., a common metric of UV radiation exposure), respectively. The UV-I value observed by the TOMS sensor is generally greater than that of the USDA ground-based measurements, and the relative error of daily change is, on average, between 5% and 12%. With these two datasets from 1999 to 2005, the trend analyses for daily and monthly UV-I change are statistically summarized at four representative stations distributed across the western U.S as an integral part of the USDA monitoring network. Spatial and temporal features may then be illuminated and retrieved according to UV-I distribution. Overall, the UV-I data acquired by the TOMS sensor can sufficiently detect the effect of spatial variation in topography, whereas continuous measurements through the USDA UV-B ground-based monitoring network can provide better temporal resolution on holistic changes in UV-I within the last few years.