Pyrgeometer

It measures the resistance/voltage changes in a material that is sensitive to the net energy transfer by radiation that occurs between itself and its surroundings (which can be either in or out).

[1] To derive the absolute downward long wave flux, the temperature of the pyrgeometer has to be taken into account.

As a result, the detected voltage and instrument temperature yield the total global long wave downward radiation.

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.