An Integrated Surface Radiation Measurement System

Abstract

An integrated surface radiation measurement system has been developed to measure the surface radiation exchange flux. The system employs upward- and downward-looking Eppley pyrgeometers and pyranometers to separately measure four components: downwelling and upwelling, as well as short- and longwave atmospheric radiation. Additional thermisters, installed by Eppley Laboratories, give a more accurate measurement of dome temperature, and the analog battery-powered thermopile temperature compensation circuit is replaced with a voltage-standard circuit. This circuit also serves to produce accurate thermisters excitation. All the parameters of the pyrgeometers, including the output of the thermopile, the temperature of the upper surface of thermopile, and the dome and the case temperatures, are monitored directly. This allows corrections to be made for the thermal emission of the thermopile and a realistic Stefan?Boltzmann calculation to correct for the solar heating of the pyrgeometer dome. The signals from the sensors are amplified, digitized, and converted to engineering units. A dedicated microprocessor calculates the required products and transmits them via a serial link. The radiometers are housed in compact assemblies that provide a lamina flow of filtered air over the sensors? domes. The four assemblies are mounted on an adjustable frame capable of being leveled to within a tenth of a degree. The leveling frame, bearing the four radiometers, is mounted on the crossbar of a radiation stand, holding the sensor 4 m above the surface. The system is transportable and can be erected and made operational in 1 h.