The micrometeorological situation inside a higher vegetation can be characterized by profiles of the relevant meteorological elements. For principal and practical reasons this is impossible when the vegetation is very low. The mean temperature of the outer vegetation surface is considered a useful micrometeorological characteristic in this case. It can be calculated from the heat radiation emitted by the surface. A radiometer is described, which permits measurements of thermal radiation even when high amounts of short-wave radiation are present. A glass shutter and a white thermopile are the characteristic features of the instrument. The great differentiation of low patchy vegetation with respect to surface temperature is illustrated by examples. The radiation method is suitable to measure leaf temperatures as well. Comparative measurements of dry and fresh leaves are given and the physical limits of transpiration cooling discussed.