Uncertainties in satellite-derived estimates of surface UV doses

Satellite‐derived maps of surface UV irradiance are currently limited by their poorly assessed accuracy. Here we use an extensive data set of ground‐based spectral measurements from two Alpine sites to examine the level of uncertainty expected in model results due to the time‐limited nature of some satellite data. When the ozone column, cloud optical depth, and aerosol optical depth supplied to a radiative transfer model are fixed to a single noontime value, the root‐mean‐square difference between calculations and measurements of the erythemal daily dose is about 20%. The corresponding uncertainty in the monthly dose is less than 5%. The modeled results also show a systematic error that depends on cloud optical depth. The results suggest that satellite‐derived maps of UV irradiance cannot be expected to produce accurate values of the daily dose if they rely on a single estimate of the cloud conditions but may be able to provide reasonable estimates of the monthly dose.