An instrument for detecting and, usually, measuring radiant energy Compare bolometer See actinometer, photometer
An instrument that quantitatively measures electromagnetic radiation Weather satellites carry radiometers to measure radiation from snow, ice, clouds, bodies of water, the Earth's surface, and the sun
An instrument for quantitatively measuring the intensity of electromagnetic radiation in some band of wavelengths in any part of the electromagnetic spectrum Usually used with a modifier, such as an infrared radiometer or a microwave radiometer