A New Method for Calibrating Reference and Field Pyranometers

Abstract

A simple method for calibrating reference pyranometers is described. Called the alternate method, it requires monitoring of direct irradiance and diffuse and global irradiance voltages without the need for a calibrated diffuse pyranometer. The method involves alternately using each of the pyranometers for monitoring diffuse and global irradiance voltages and then solving pairs of simultaneous equations for each available zenith angle, where the only unknowns are the directional responses of the pyranometers being calibrated. Results from models and field calibrations show that the uncertainties of the alternate method are less than 1% for solar zenith angles less than 75° and are equal to or better than those determined from the composite method under identical conditions. The new method calibrations am also in good agreement with sun-disk method calibrations. It is argued that by using the alternate method for on-site field calibrations the uncertainties in network measurements can be reduced.