Measuring terrestrial radiation

In reading up about infrared light in www.wikipedia.org I ran into this device, a precision infrared radiometer. It is used to measure changes in the atmosphere due to incoming solar rays and outgoing due to reflections (mostly in the infrared wavelength). They are constructed with a Eppley thermopile which has built in error that can be handled using these procedures provided by Gayle Dana. Well, after reading all that and knowing that they calculated radiation flux, I still needed to turn back to wikipedia to find out that a thermopile takes radiation and turns it into an electrical current. The infrared radiometer is used in measuring global warming effects, which is a rather complicated problem. It can be used on land, water or in the air, with a variety of differences in error.