Laboratory calibration of pyrgeometers with known spectral responsivities

A methodology is presented to calibrate pyrgeometers measuring atmospheric long-wave radiation, if their spectral dome transmission is known. The new calibration procedure is based on a black-body cavity to retrieve the sensitivity of the pyrgeometer, combined with calculated atmospheric long-wave spectra to determine a correction function in dependence of the integrated atmospheric water vapor to convert Planck radiation spectra to atmospheric long-wave spectra. The methodology was validated with two custom CG4 pyrgeometers with known dome transmissions by a comparison to the World Infrared Standard Group of Pyrgeometers at the World Radiation Center-Infrared Radiometry Section. The responsivities retrieved using the new laboratory calibration agree to within 1% with the responsivities determined by a comparison to the WISG, which is well within the uncertainties of both methodologies. (c) 2007 Optical Society of America