The available energy over a Scots Pine plantation: What's up for partitioning?

Errors influencing the calculation of the available energy above a forest are discussed. The main emphasis is put on the investigation of the problems affecting the measurement of net radiation. This is done by utilizing the data set of a surface energy balance experiment which was conducted in and above a Scots Pine plantation from May 11 to 22, 1992. During that Hartheimer Experiment (HartX) there were redundant measurements of net radiation using five different radiometers of three different designs. The initially fair agreement between the net radiometer readings was considerably improved by introducing different responsivities for the shortand longwave range. The mean deviations to the relative net radiation after correction vary between — 1.4 and 1.2 Wm−2 with standard deviations between ± 5.4 and 6.6 Wm−2. The total error referring to the available energy is estimated to be up to ± 36 Wm−2 (± 6%) around midday decreasing to 10 Wm−2 during nighttime.