Comparisons of corrected daily integrated erythemal UVR from the U.S. EPA/UGA network of Brewer spectroradiometers with model and satellite data

A network of 21 Brewer spectroradiometers, owned by the U.S. Environmental Protection Agency and operated by the University of Georgia, is measuring UV spectral irradiances throughout the United States. Corrections to the raw data have now been implemented. These corrections include (1) stray light rejection, (2) the cosine errors associated with the full sky diffuser, (3) the temperature dependence of the response of the instruments and (4) the temporal variation in the instrument response due to optical changes in the characteristics of the instruments. While for many sites the total corrections amount to less than 10%, for certain sites they are much larger, in some cases amounting to more than 25%. Application of these corrections brings the errors of the absolute irradiance values to approximately ± 5 to 7% for all sources of error. Comparisons of corrected daily integrated erythemal UVR data (DUV) to model and TOMS-inferred values are performed for sites at Acadia National Park, Bigbend National Park, Everglades National Park and the Virgin Islands. All sites show very good agreement with the TUVSPEC model but comparison with TOMS-inferred DUV values indicate a 10-20% overestimate by TOMS for the four sites.