Monochromatic all-sky scanner: a quantitative imager of faint atmospheric emissions

Many ground-based studies of the dynamics of the lower thermosphere and ionosphere have been performed using meridian scanning photometers and all-sky cameras. The two instruments strike different balances between quality and quantity or sensitivity versus large field of view. A large divergence angle in a wide-angle system requires large bandwidth filters that limit detectability of faint atmospheric emissions that are due to low signal-to-background ratio. All-sky imaging to as low as 80-deg zenith angle is important in addressing issues such as horizontal wavelength of individual waves and size of wave packets in the neutral atmosphere, and size and dynamics of red arcs and F-layer patches. A new instrument for remote sensing of the Earth's upper atmosphere and its near-space environment from the ground is described. It affords true all-sky imaging at near-monochromatic wavelengths for faint airglow and auroral emissions by combining a two-mirror scanner with a zenith-looking photometer.