Global Ultraviolet Imager (GUVI) for the NASA Thermosphere-Ionsphere-Mesosphere Energetics and Dynamics (TIMED) mission

Abstract
The global ultraviolet imager (GUVI) investigation is designed to provide quantitative observations and interpretation of the Earth's airglow and auroral emissions in support of the NASA thermosphere, ionosphere, mesosphere, energy and dynamics (TIMED) mission. It addresses TIMED objectives dealing with energetics, dynamics, and the specification of state variables. The instrument provides multiple-wavelength, simultaneous `monochromatic' images of the far-ultraviolet emission (115 to 180 nm) using a scan mirror to sweep the instantaneous field of view of a spectrographic imager through an arc of up to 140 degree(s) aligned perpendicular to the orbit plane of the spacecraft. The instantaneous field of view is 11.8 degree(s) by 0.37 degree(s) (adjustable) along the slit and perpendicular to the slit, respectively. The field of view is mapped to a two-dimensional image plane with up to 64 spatial pixels by 160 spectral pixels of spectral width 0.4 nm per pixel. Binning of pixels can be performed along both the spatial and spectral axes of the array to reduce the demands on the downlink telemetry. The f/3 Rowland circle scanning spectrographic imager is outfitted with a toroidal grating ruled at 1200 grooves per millimeter. The fore-optics consists of a plane scanning mirror and an off-axis parabolic telescope. The detector is a photon-counting microchannel plate with a wedge and strip anode mounted in a sealed tube.

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