TV- and all-sky-cameras (ASC)
To be written. For the time being, see the information of the All Sky Camera chain of the Finnish Meteorological Institute.
Photometers measure the absolute luminous intensity of a light source. Because of the monochromatic nature of the auroral light, photomultiplier tubes with very narrow band filters were used in the measurements. The typical wavelengths that have been measured are:
From these emissions one can make estimates of the characteristic energy and energy flux of the auroral particle precipitation, especially when the measurements are made along the field line the particles (in most cases electrons) are coming down. The photometers are, however, often made to operate in two possible modes, i.e., field aligned or scanning. In the scanning mode a moving mirror is used to scan a larger part of the sky, to get a broader view of the auroral distribution. With typical quiet, slowly drifting east-west aligned auroral arcs this gives good results when the scanning is done along the magnetic meridian. For example Doe et al. (1997) have discussed a tomographic method to utilize this kind of optical data.