Optimizing the precision of infrared measurements using the Eppley Laboratory, Inc. model PIR pyrgeometer

Abstract

The Eppley Precision Infrared Radiometer (PIR) is widely used for broadband (3.5–50 µm), thermal infrared wavelength measurements of the downwelling and upwelling radiation from the atmosphere and surface, respectively. The field of view of the instrument is 2π steradians with a receiver that has an approximate cosine response. In this paper we examine four equations suggested by the literature that have been used to transfer irradiance calibrations from our standard PIRs that are calibrated at the World Radiation Center to field units used for network operations. We first discuss various equations used to convert the resistance measurements of the thermistors to temperatures of the body and dome that are used in the derivation of incoming irradiance. We then use the four related, but distinct, equations for the transfer of the calibration from standard PIRs to field instruments. A clear choice for the preferred equation to use for calibration and transfer of calibration to field PIRs emerges from this study.