Pyrgeometer is a device that measures the atmospheric infra-red radiation spectrum that extends approximately from 4.5 µm to 100 µm. Pyrgeometers are designed for IR (infrared) radiation measurement, for both atmospheric and material testing research applications. Pyrgeometers are frequently used in meteorology, climatology studies. The atmospheric long-wave downward radiation is of interest for research into long term climate changes. The signals are generally detected using a data logging system, capable of taking high resolution samples in the millivolt range.

Infrared radiation generally refers to long wavelength radiation of more than 3.0ƒÊm. Long wave radiation is emitted by all objects that exist on the earth. However, the principal purpose for pyrgeometers is meteorological observation of atmospheric radiation (radiation from clouds, vapor, CO2 etc.), and the net radiation from between the earth and atmosphere. The measurement of long wave radiation is more difficult technically than the measurement of solar radiation. For this reason, International Standards for the measurement of long wave radiation have not been developed.

Pyrgeometer Operating Principle

pyrgeometer uses a thermopile to detect thermal gradients caused by incoming radiant energy. The detecting element is a black painted disk, which absorbs the incoming radiation, and the heat flows through to the heatsink, which is the instrument body. The thermal gradient across the thermopile produces a voltage which is proportional to the net radiation. (ie the difference between the radiation received at the detector, and the radiation emitted by the pyrgeometer itself). The spectral range of the incoming radiation is restricted by a specially coated silicon window, which filters out unwanted solar radiation below wavelengths of 4.5mm. The silicon window is also required to protect the instrument from environmental effects, such as wind and rain.