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

Abstract. The Eppley Model PIR is widely used for thermal infrared wavelength (3.5–50 μm) 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 in the literature that have been used to transfer calibration from standards to field units that are used for network operations. After the introduction we discuss various equations used to convert the resistance of the YSI 44031 thermistors used in PIRs for temperature measurements of the body, aka case, 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 standards 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.