Auroral spectral estimation with wide-band color mosaic CCDs

Optical aurora can be structured over a wide range of spatial and temporal scales with spectral features that de- pend on the energy of precipitating particles. Scientific stud- ies 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 de- vices provide sequences of two dimensional multispectral lu- minosity 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 inver- sion was used to better understand the effective spectral res- olution of existing and proposed instruments. Two spectrally calibrated commercial detectors (Sony ICX285AQ and ICX429AKL) with very different color mo- saics (RGB (red, green, blue) vs. CYGM (cyan, yellow, green, magenta)) were found to have very similar spec- tral 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 con- figurations. Operating the ICX429AKL in a noninterlaced mode would improve spectral resolution and provide an addi- tional near infrared channel. Transformations from arbitrary device channels to RGB are easily obtained through inver- sion. 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.