Recording Hydroxyl spectra

The workhorse of measurements of the temperature at the height of the Hydroxyl layer has been 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

Spectra of parts of the Hydroxyl airglow emission have been measured above Davis station, Antarctica, (68.6°S, 78.0°E) with a Czerny-Turner spectrometer since 1990.

The element that splits the incoming light into its component parts is called a diffraction grating. This consists of 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.