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Ann. Geophys., 25, 519-532, 2007
www.ann-geophys.net/25/519/2007/
© European Geosciences Union 2007
A Wide Field Auroral Imager (WFAI) for low Earth orbit missions
N. P. Bannister1, E. J. Bunce1, S. W. H. Cowley1, R. Fairbend2, G. W. Fraser1, F. J. Hamilton1, J. S. Lapington1, J. E. Lees1, M. Lester1, S. E. Milan1, J. F. Pearson1, G. J. Price1, and R. Willingale1
1Department of Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
2Photonis SAS, Avenue Roger Roncier, Brive, 19410 Cedex, France
Abstract. A comprehensive understanding of the solar wind interaction with Earth's
coupled magnetosphere-ionosphere system requires an ability to observe the
charged particle environment and auroral activity from the same platform,
generating particle and photon image data which are matched in time and
location. While unambiguous identification of the particles giving rise to
the aurora requires a Low Earth Orbit satellite, obtaining adequate spatial
coverage of aurorae with the relatively limited field of view of current
space bourne auroral imaging systems requires much higher orbits. A goal for
future satellite missions, therefore, is the development of compact, wide
field-of-view optics permitting high spatial and temporal resolution
ultraviolet imaging of the aurora from small spacecraft in low polar orbit.
Microchannel plate optics offer a method of achieving the required
performance. We describe a new, compact instrument design which can observe
a wide field-of-view with the required spatial resolution. We report the
focusing of 121.6 nm radiation using a spherically-slumped, square-pore
microchannel plate with a focal length of 32 mm and an F number of 0.7.
Measurements are compared with detailed ray-trace simulations of imaging
performance. The angular resolution is 2.7±0.2° for the prototype,
corresponding to a footprint ~33 km in diameter for an aurora altitude
of 110 km and a spacecraft altitude of 800 km. In preliminary analysis, a
more recent optic has demonstrated a full width at half maximum of 5.0±0.3
arcminutes, corresponding to a footprint of ~1 km from the same
spacecraft altitude. We further report the imaging properties of a convex
microchannel plate detector with planar resistive anode readout; this
detector, whose active surface has a radius of curvature of only 100 mm, is
shown to meet the spatial resolution and sensitivity requirements of the new
wide field auroral imager (WFAI).
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