Description
The hyperspectral camera for auroral imaging (HySCAI), which can provide a two-dimensional (2D) aurora image with full-spectrum coverage, was developed to explore a new frontier in auroral optical observation. HySCAI consists of an all-sky lens, a monitor camera, a galvanometer scanner that scans a slit image of the spectrograph onto the all-sky image plane, a grating spectrograph, and an electron-multiplying charge-coupled device (EM-CCD). HySCAI has two gratings: one with 500 grooves/mm for a wide spectral coverage of 400–800 nm and a spectral resolution (FWHM) of 2.1 nm, and the other with 1500 grooves/mm for a higher spectral resolution of 0.73 nm and a narrower spectral coverage of 123 nm. This system was installed at the KEOPS (Kiruna Esrange Optical Platform Site) of the SSC (Swedish Space Corporation) in Kiruna, Sweden, in 2023 [1]. Unlike conventional filter-based cameras, HySCAI captures more than 25 monochromatic images simultaneously, enabling quantitative auroral measurements even under twilight conditions by accounting for background emission. It also provides the spectral shapes of molecular bands. Three key results have been obtained: 1) The two-dimensional distribution of precipitating electron energy, derived from intensity ratios I(427.8nm)/I(630.0nm) and I(557.7nm)/I(630.0nm), shows a sudden increase to 1–2 keV during auroral breakup [2]. 2) The altitude profile of N₂⁺ density, determined from the 427.8 nm resonance scattering emission, peaks at 200 km [3], significantly higher than the 130 km predicted by the GLOW model. 3) The rotational temperature of nitrogen, obtained from N₂ 1PG and Meinel band spectra, is higher on the north (polar) side and increases with time during red auroral expansion. Data and related resources are available at the Data Repository Aurora Imaging Spectroscopy (DRAIS) in the National Institute for Fusion Science (NIFS) [4]. A second system, HySCAI-2, is under development for installation at Showa Station, Antarctica. It will offer higher spectral resolution for proton aurora velocity measurements and polarization-resolved measurements to investigate electron anisotropy.
[1] Aurora Observation Project https://projects.nifs.ac.jp/aurora/en/
[2] M.Yoshinuma, K.Ida, Y.Ebihara, Earth, Planets and Space 76 (2024) 96.
[3] K.Ida, Y.Ebihara, M.Yoshinuma, K.Shiokawa, Geophys. Res. Lett. 52 (2025) e2025GL118375.
[4] Data Repository Aurora Imaging Spectroscopy (DRAIS) https://doi.org/10.57451/nifs.aurora‐project