Observations of the biophysical environment are essential in agricultural research, including forestry and livestock. The physical elements of climate are observed in order to assist in the evaluation of actual and future land use potentials and of such constraints in agriculture as are caused by the environment. To meet these requirements, agricultural meteorology needs reliable, quantitative data on the relevant climatic elements. 1.12 Indispensable climatic elements in agricultural meteorology include those pertaining to geographical climatology and especially those permitting interpretation of physical processes in the lower layers of the atmosphere and the upper soil layers. Elements pertaining to energy and water balance are thus very important, as well as other related phenomena, such as humidity, temperature, wind and precipitation. 1.1.3 In agricultural meteorology, macro and micro scale observations are required. While macro-scale observations provide information on the climatic background, most of the agricultural planning and research activities require data on the meso- or micro -climatic scales. Standard instrumentation and standard exposure conditions in agricultural meteorology, are important as far as comparability is concerned. However, in research work, instruments and exposure conditions are not always standard.