Investigations in Pyranometer Design

Abstract

Three approaches to the design of total (global) solar pyranometers that employ new technologies and materials of manufacture are described. The pyranometers are designed to meet or exceed the requirements for high quality instruments as classified by the World Meteorological Organization?s Guide to Meteorological Instruments and Methods of Observation. A pyranometer employing linear thin-film platinum resistance thermometers to measure the temperature rise of an optically black metal surface is presented; a second design utilizes a bismuth telluride thermopile to measure the temperature rise of an optically black silver disc, and a third design uses an optically black, fast-response thin film bismuth antimony thermopile with diffusing foreoptic for determining the solar irradiance level. All three designs employ optically black radiation receiving surfaces. The structure of the radiation detection schemes are presented and electronic circuitry, when required, is described. For each of the instrument types, the measured time responses, ambient temperature response, cosine response, and azimuth asymmetry response are presented. Special-purpose apparatus used for determining cosine response and azimuth response is presented in the appendix.