The workhorse of measurements of the temperature at the height of the Hydroxyl layer, is the Czerny-Turner scanning spectrometer. The name comes from Czerny and Turner, the designers who first used this combination of lenses, slits and gratings to make a spectrometer.
Czerny-Turner scanning spectrometer
A Czerny-Turner spectrometer Spectra has been measuring parts of the Hydroxyl airglow emission above Davis station since 1990.
The element that splits the incoming light into its component parts is called a diffraction grating. This is a mirror with closely spaced fine lines cut into its surface. By rotating the mirror, the portion of the spectrum being measured can be shifted in wavelength. This scanning action allows a spectrum of the light to be obtained.
A system of mirrors and lenses transfer light from the sky through a hatch in the roof and into the spectrometer. A sensitive detector known as a photomultiplier tube is used to measure the intensity of the faint emissions being measured.