Standard Meteorological Measurements

Instruments that measure weather variables have been invented and tested since the time of Leonardo de Vinci. The earliest instruments were crude by today’s standards and required manual observation and notation of the weather variable of interest. In recent years, the miniaturization of circuits–sensors and the use of electronic processors have made it possible to collect ever-increasing numbers of observations on scales not previously considered. In many agricultural applications, the primary portion of the atmosphere that is of interest is the lower planetary boundary layer, or that layer affected by the earth’s surface. Accurate measurement of weather variables in the lower planetary boundary layer requires an understanding of the interactions among the atmosphere, plant communities, and soils. Temperature and pressure are often measured because of their role in air movement and energy exchange between the earth’s surface and the atmosphere. Temperature is perhaps of greater interest in agricultural applications because it is a driving variable that determines the rate of growth and development of an organism, and thus determines what species can grow in a region. Wind speed and direction are measured because of their role in convective energy exchange and the movement of spores, pollen, odors, and chemicals as they drift in the atmosphere. Precipitation amount, intensity, frequency, and form are important in determining the availability of water for crops and play an important role in soil erosion by water and in water quality issues. Solar radiation and relative humidity are additional weather variables, important to agriculture, that are often measured by appropriate sensors at automated weather stations. These variables will be discussed by Klassen and Bugbee (2005, this volume) and Campbell and Diak (2005, this volume)