Development of hyperspectral camera for auroral imaging (HySCAI)

Abstract

The hyperspectral camera for auroral imaging (HySCAI), which can provide a two-dimensional (2D) aurora image with full spectrum, was developed to study auroral physics. HySCAI consists of an all-sky lens, monitor camera, galvanometer scanner, grating spectrograph, and electron multiplying charge coupled device (EM-CCD). The galvanometer scanner can scan a slit image of the spectrograph on the all-sky image plane in the direction perpendicular to the slit. HySCAI has two gratings; one is 500 grooves/mm for a wide spectral coverage of 400–800 nm with a spectral resolution (FWHM) of 2.1 nm, and the other is 1500 grooves/mm for a higher spectral resolution of 0.73 nm with a narrower spectral coverage of 123 nm. The absolute sensitivity is 2.1 count/s/R with 4 × 4 binning (256 × 340 image) at 557.7 nm. The exposure time depends on the brightness of the aurora emission and is typically 64 s for a 2D image (0.2 s per line scan). This system has been installed at the KEOPS (Kiruna Esrange Optical Platform Site) of the SSC (Swedish Space Corporation) in Kiruna, Sweden. All-sky images with a liquid crystal filter and a sky color camera have also been installed to compensate for the poor time resolution of HySCAI. 2D aurora monochromatic images for given wavelength are obtained by reconstructing the EM-CCD image over the scan period. HySCAI has the advantage of providing a 2D image of intensity for a weak emission line, which appears on top of a high background emission without the contamination from other emissions, which is usually difficult in a system with a bandpass filter. As the first light results, monochromatic images of N⁺[₂] 1NG (0, 1) (427.8 nm), N⁺[₂]1NG (0, 2) (470.9 nm), H[β] (486.1 nm), N II (500.1 nm), NI (²D) (520.0 nm), OI (¹S) (557.7 nm, ), NaD (589.3 nm), O I (¹D) (630.0 nm), and N⁺[₂] 1NG (670.5 nm) emission intensity were measured. We estimated the precipitating electron energy from a ratio of I(630.0 nm)/I(427.8 nm) to be 1.6 keV.