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The design of a multi-mode instrument known as the Auroral Ionospheric Remote Sensor, AIRS, is described. The design criteria are enumerated. The goal of the AIRS instrument is to produce data on the global imaging of the auroral display in both dark and sunlit hemispheres with the remote sensing of ionospheric airglows to deduce ionospheric parameters such as electron density profiles and atmospheric background emissions. The AIRS will fly on the POLAR BEAR spacecraft in a near polar circular orbit at an altitude of 1,000 km with a scheduled launch in the fall of 1986. The AIRS instrument is designed as a multi-mode system with four (4) channels of data to yield simultaneous operation in the vacuum ultraviolet (VUV), near ultraviolet (UV) and visible spectral bands. Two of the data channels are designed to operate in the VUV with 30A windows having a 240Å separation. These two channels utilize an Ebert-Fastie spectrometer which can provide total coverage for each of these channels from 1150Å to 1800Å. The other two channels utilize a filter selector system to provide preselected, 10Å bandwidth spectral channels at 3371Å, 3914Å and 6300Å, and a 200Å wide channel centered at 2250Å. These spectral bands are paired to provide simultaneous pair coverage of 2250Å and 3371Å and simultaneous pair coverage of 3914Å and 6300Å. All four channels view the auroral scene of the north polar cap via appropriate optics and a scan mirror system. In effect a line scan image of the auroral scene is produced via the scan mirror operating in the orbit cross plane with the longitudinal direction provided by the forward motion of the spacecraft. All four channels can also operate in the photometer mode by locking of the scan mirror in the nadir viewing position. The two VUV channels can also operate in a spectrometer mode with the scan mirror locked in the nadir viewing position and the Ebert-Fastie spectrometer performing a spectral scan. The basic ground level spatial resolution at nadir of the four (4) spectral channels is 6.5 km x 26.7 km for the VUV channels and 26 km x 39.26 km for the near UV, visible channels. All four channels are spatially aligned to view the same scene pixel area simultaneously. The instrument sensitivity is designed to result in 50 Rayleigh detection levels for the VUV channels and approximately 1K Rayleigh detection levels for the near UV, visible channels. The total system operates at a maximum average power level of 9.3 watts in the imaging mode with a data rate of 0.884 K bits per second per channel. The total instrument weight is 23.0 lbs.
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