Abstract
From routine hourly observations reported during 5 years at one site in Denmark, empirical relations for net radiation over green grass are found. These relations give an estimate of the net radiation for the measuring site from the geographical position, local time, representative surface albedo, measured global radiation and/or total cloud cover in oktas. Cloud types are taken into account, if the reported clouds are mainly cirrus forms. This is a result of a classification of the net radiation according to cloud cover and type, i.e. a total of 90 classes. Different relations are found for different cloud covers.
The derived procedure is used on another site in Denmark with another representative surface albedo. From 10 years of data, consistency is found for net radiation measurements at the two sites, allowing extrapolation of the derived net radiation procedure to other sites in Denmark. Data from the Wangara experiment (Clarke, 1971), covering 40 days, showed a similar relation for clear sky conditions, but revealed another general dependency of net radtation upon cloud cover than that found in Denmark. Therefore, relations of the kind found in this study are related to the weather and climate of the measuring site. Comparisons between net radiation estimated from the models and measurements from different sites is r^2^ β 0.9.