Using colour in auroral imaging

The prototype of an auroral colour camera named Rainbow was run at the Auroral Station in Adventdalen, Svalbard, Norway, during a Finnish optical campaign in February, 2004. Instead of narrow band-pass filters and grey-scale images, this imager records colour images of the aurora using four wide-band channels (a colour CCD) with the field-of-view of about 150°. In this study, 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 (557.7 nm), red (630.0 nm), and blue (427.8 nm), which were simultaneously recorded by the meridian scanning photometer (MSP) at the same station. This fit is qualitatively extremely good and almost linear throughout the data. In studying the auroral evolution during substorms, there is no significant difference whether MSP or Rainbow data are used. However, due to wide-band colour channels, the background illumination has a strong effect on the Rainbow data. During low signal levels (only background or faint aurora) the reconstruction errors are larger. The data for this study were captured on 21 February 2004. The time period of interest includes a substorm sequence, which is examined using colour auroral images and data from the MSP. PACS No.: 94.20.Ac