cavity radiometer
From Glossary of Meteorology
A modern, self-calibrating pyrheliometer or device for measuring direct solar radiation.
The receiver (cavity) is typically conical in shape with precision temperature sensors and heaters. Operating at an equilibrium temperature, direct electrical power to the heater is decreased if solar radiation is added to the receiver (or added if solar radiation is removed). The electrical power necessary to maintain equilibrium is equivalent to the change in incident solar radiation.
