USDA UV-B monitoring system: An application of centralized architecture

In order to determine the spatial and temporal variations of solar ultraviolet-B (UV-B) radiation reaching the Earth's surface and their effects on agriculture and environment due to the depletion of atmospheric ozone, the U.S. Department of Agriculture (USDA) UV-B monitoring system has been established to provide essential information of ground UV-B levels, along with other variables, to research communities, decision makers, and the public. This monitoring network of 39 sites was designed as a centralized system covering the U.S. domain with collaborating sites in Canada and New Zealand. Programmed data loggers and a central data server are employed to automate the work. The centralized architecture allows centrally processing the data from all sites on a 3 min basis and making daily updates available for the users. The system architecture, algorithms for data collection and data flow in the data processing procedures are presented in this article. Statistics show that the system is rather reliable with an overall data completeness of 98.14% since it began running in 1994. Main damages to the instruments are caused by the static electricity associated with severe thunderstorms, which result in a lower data completeness in summer months than in the others. The drawbacks of the centralized architecture, the possible remedies for the network failures, and our experiences with the system are discussed.