Pyrgeometer

A pyrgeometer is the instrument used to measure the Infrared thermal radiation (FIR) emitted by the artmosphere. In effect, a pyrgeometer provides a voltage that is proportional to the radiation exchange between the instrument and the sky (or ground) in its field of view. The detector signal output can be positive or negative.

For example, if the sky is colder than the pyrgeometer, the instrument radiates energy to the sky and the output is negative.
In order to calculate the incoming or outgoing FIR it is necessary to know the temperature of the instrument housing close to the detector and the data must be recorded simultaneously with the detector signal.

The typical wavelenght range cover the relevant part of radiation emitted by Earth atmosphere:
4.0 µm till about 50 µm. This range is very different from solar radiatrion since the atmosphere is much cooler of sun surface. The dome is made in silicon to cover this spectral range, and its shape is usually realized in such a way to reduce solar influence if the instrument dome is not shaded.

Technical specifications reported here are those of a top class instrument. The 3D model is based on the Kipp & Zonen CGR4 pyrgeometer.