Colour imaging of the aurora

Partamies, N., Syrjäsuo, M. and Kauristie, K.

Finnish Meteorological Institute, Helsinki, Finland

Most of the auroral imaging nowadays is performed by using either white light imagers or cameras with narrow band-pass filters centered at the most common auroral emission lines: green at 557.7nm, blue at 427.8nm and red at 630.0nm. Imagers utilising the filters provide quantitative information on emissions at each wavelength, but they are also very expensive and replacing worn-out parts can be costly. White light (panchromatic) imagers, on the other hand, lose all the spectral information but can provide high temporal resolution of the evolution of the aurora at a lower cost.

Colour imaging has been investigated as an option by University of Calgary to help the automatic detection of the aurora from the growing amount of imager data. A prototype imager called Rainbow was run during a Finnish optical and EISCAT campaign at the auroral station on Svalbard in February, 2004. In our preliminary study of these colour data, we show the results of fitting the four Rainbow channels (cyan-magenta, cyan-green, yellow-magenta, yellow-green) to reconstruct the traditionally filtered auroral wavelengths: green (557.7nm), red (630.0nm) and blue (427.8nm) which were simultaneously recorded by the Meridian Scanning Photometer (MSP) at the same station. This fit is qualitatively surprisingly good and almost linear. We show that using colour imagers instead of white light cameras provides us with a possibility to reconstruct some spectral information in addition to the great public outreach component. At the moment, six all-sky colour cameras are operating continuously in the Northern auroral zone, and more are being deployed.