1Physics and Astronomy Department, University of Calgary, Calgary, Canada
2School of Electrical Engineering, Aalto University, Espoo, Finland
3Finnish Meteorological Institute, Helsinki, Finland
4Department of Physics, Lancaster University, Lancaster, UK
5British Antarctic Survey, Cambridge, UK
6Department of Physics and Astronomy, University College London, London, UK
7SRI International, Menlo Park, California, USA
Received: 03 Nov 2013 – Discussion started: 23 Dec 2013
Abstract. Optical aurora can be structured over a wide range of spatial and temporal scales with spectral features that depend on the energy of precipitating particles. Scientific studies typically combine data from multiple instruments that are individually optimized for spatial, spectral, or temporal resolution. One recent addition combines all-sky optics with color mosaic CCD (charge-coupled device) detectors that use a matrix of different wide-band micro-filters to produce an image with several (often three) color channels. These devices provide sequences of two dimensional multispectral luminosity with simultaneous exposure of all color channels allowing interchannel comparison even during periods with rapidly varying aurora. At present color auroral image data are primarily used for qualitative analysis. In this study a quantitative approach based on Backus–Gilbert linear inversion was used to better understand the effective spectral resolution of existing and proposed instruments.
Revised: 28 Apr 2014 – Accepted: 01 May 2014 – Published: 11 Jun 2014
Two spectrally calibrated commercial detectors (Sony ICX285AQ and ICX429AKL) with very different color mosaics (RGB (red, green, blue) vs. CYGM (cyan, yellow, green, magenta)) were found to have very similar spectral resolution: three channels with FWHM (full-width half-maximum) ≈100 nm; a NIR (near infrared) blocking filter is important for stabilizing inversion of both three-channel configurations. Operating the ICX429AKL in a noninterlaced mode would improve spectral resolution and provide an additional near infrared channel. Transformations from arbitrary device channels to RGB are easily obtained through inversion. Simultaneous imaging of multiple auroral emissions may be achieved using a single-color camera with a triple-pass filter. Combinations of multiple cameras with simple filters should provide ~50 nm resolution across most of the visible spectrum. Performance of other instrument designs could be explored and compared using the same quantitative framework.
Jackel, B. J., Unick, C., Syrjäsuo, M. T., Partamies, N., Wild, J. A., Woodfield, E. E., McWhirter, I., Kendall, E., and Spanswick, E.: Auroral spectral estimation with wide-band color mosaic CCDs, Geosci. Instrum. Method. Data Syst., 3, 71-94, doi:10.5194/gi-3-71-2014, 2014.