Radiometer is a device for measuring the radiant flux power of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength. A microwave radiometer operates in the microwave wavelengths. The radiometer contains argon gas to enable it to rotate. The MEMS radiometer can operate over a wide spectrum of wavelength and particle energy levels.

In optics, radiometry is the field that studies the measurement of electromagnetic radiation, including visible light. Note that light is also measured using the techniques of photometry, which deal with brightness as perceived by the human eye, rather than absolute power. Radiometry is important in astronomy, especially radio astronomy, and is important for Earth remote sensing. The measurement techniques categorized as radiometry in optics are called photometry in some astronomical applications, contrary to the optics usage of the term. Spectroradiometry is the measurement of absolute radiometric quantities in narrow bands of wavelength.

Microwave Radiometers

Microwave radiometer (MWR) is a radiometer that measures energy emitted at sub-millimetre-to-centimetre wavelengths (at frequencies of 1-1000 GHz) known as microwaves. Their primary application has been onboard spacecraft measuring atmospheric and terrestrial radiation, and they are mostly used for meteorological or oceanographic remote-sensing. Their secondary application is also meteorological, as zenith-pointing surface instruments that view the Earth’s atmosphere in a region above the stationary instrument.

Ultraviolet (UV) Radiometers

Narrowband and broadband scientific Ultraviolet (UV) Radiometers are used for measuring the spectral response that is adapted to the erythemal (sunburn) action spectrum of the human skin. UV radiometers have an analogue voltage output which is proportional to the measured UV irradiance. Measuring solar UV radiation is difficult because the spectral distribution of atmospheric UV irradiance is very variable, mainly depending on sun elevation and stratospheric ozone.