Atmospheric extinction at the Brno and Skalnate PlesoObservatories I. Instrumentation, observations and review ofdata

Two extensive collections of UBV photoelectric measurements of atmospheric extinction obtained at the Skalnate Pleso Observatory and at the Masaryk University Observatory in Brno from 1962 to 1995 were analyzed for the nature of extiction and for seasonal and long-term variations as well. In the present paper (Paper I) the instrumentation used, observations, and general characterizations of the data are discussed. Interpretation of the data is the subject of the Paper II that will occur in 2001, in summer volume of the journal.