Table 2 Key properties of the NIRAS, both the spectrometer and the detector are manufactured by HORIBA Scientific. Typical operational parameters are also shown
| Specifications of the NIRAS | ||
|---|---|---|
| Spectrometer | Czerny-Turner | |
| Focal length | 320 mm | |
| \(\textit{F}\) number | 4.1 | |
| Slit width | 0.10 mm (0–2 mm, electrically controlled) | |
| Etendue | 0.014–\(0.017\,\text {cm}^2\)*sr | |
| Field-of-view | \(0.019^{\circ }\times 0.19^{\circ }\) | |
| Detector | InGaAs 1-D array | |
| Pixel size | 25 μm × 250 μm (\(\text {W} \times \text {H}\)) | |
| Number of pixel | 1024 | |
| Operation temperature | \(-52.0 \pm 0.2\,^{\circ }\text {C}\), thermoelectric cooling | |
| Grating | 600 lpmm | 150 lpmm |
| Blaze wavelength | 1500 nm | 1200 nm |
| Spectral sampling | 0.11 nm/pixel | 0.50 nm/pixel |
| Spectral resolution | \(\ge 0.42 \,\text {nm}\) | \(\ge 1.9 \,\text {nm}\) |
| Spectral range | 119 nm | 510 nm |
| Observation setting of the NIRAS | ||
|---|---|---|
| Observation condition | Syowa: SZA \(\ge 100^{\circ }\), Kiruna: SZA \(\ge 96^{\circ }\) | |
| Center of field-of-view | Syowa: local magnetic zenith (\(63.4^{\circ }\)), Kiruna: local zenith | |
| Temporal resolution | 30 s (exposure 29 s) | |
| Data acquisition cycle | 3 min: 1 dark frame and 5 sky frames | |
| Airglow target | OH Meinel (3,1) band with the 600-lpmm grating | |
| Aurora target | \(\text {N}^+_2\) Meinel band and \(\text {N}_2\) 1st positive band with the 150-lpmm grating | |