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Abstract

Direct imaging of the magnetosphere by the IMAGE spacecraft will be supplemented by observation of the global aurora, the footprint of magnetospheric regions. To assure the simultaneity of these observations and the measurement of the magnetospheric background neutral gas density, the IMAGE satellite instrument complement includes three Far Ultraviolet (FUV) instruments. In the wavelength region 120-190 nm, a downward-viewing auroral imager is only minimally contaminated by sunlight, scattered from clouds and ground, and radiance of the aurora observed in a nadir viewing geometry can be observed in the presence of the high-latitude dayglow. The Wideband Imaging Camera (WIC) will provide broad band ultraviolet images of the aurora for maximum spatial and temporal resolution by imaging the LBH N 2 bands of the aurora. The Spectrographic Imager (SI), a monochromatic imager, will image different types of aurora, filtered by wavelength. By measuring the Doppler-shifted Ly-α, the proton-induced component of the aurora will be imaged separately. Finally, the GEO instrument will observe the distribution of the geocoronal emission, which is a measure of the neutral background density source for charge exchange in the magnetosphere. The FUV instrument complement looks radially outward from the rotating IMAGE satellite and, therefore, it spends only a short time observing the aurora and the Earth during each spin. Detailed descriptions of the WIC, SI, GEO, and their individual performance validations are discussed in companion papers. This paper summarizes the system requirements and system design approach taken to satisfy the science requirements. One primary requirement is to maximize photon collection efficiency and use efficiently the short time available for exposures. The FUV auroral imagers WIC and SI both have wide fields of view and take data continuously as the auroral region proceeds through the field of view. To minimize data volume, multiple images are taken and electronically coadded by suitably shifting each image to compensate for the spacecraft rotation. In order to minimize resolution loss, the images have to be distortion-corrected in real time for both WIC and SI prior to co-adding. The distortion correction is accomplished using high speed look up tables that are pregenerated by least square fitting to polynomial functions by the on-orbit processor. The instruments were calibrated individually while on stationery platforms, mostly in vacuum chambers as described in the companion papers. Extensive ground-based testing was performed with visible and near UV simulators mounted on a rotating platform to estimate their on-orbit performance. The predicted instrument system performance is summarized and some of the preliminary data formats are shown.

The THEMIS Array of Ground-based Observatories for the Study of Auroral Substorms

“…Although each exposure is only a 10-second integration, the 2 minute rotation period of the IMAGE satellite restricted the time resolution to about 2 minutes. THEMIS ground-based observatories need to make quasi-global images at a much higher repetition rate (Mende et al 2000) (Fig. 2).…”

On ULF Signatures of Lightning Discharges

“…It should, however, be stressed that the local resonances in the mesosphere and ionosphere above lightning discharges may have far reaching consequences in the entire complex of atmosphere-ionosphere-magnetosphere coupling especially in view of thousands of thunderstorms world-wide at any time. It would be nowadays possible to check on lightning induced energetic proton precipitation in analogy to LEP by means of the Far UltraViolet imager onboard the IMAGE spacecraft which provides a global display of proton precipitation regions detached form the main auroral oval (Mende et al 2000). This method has been successfully applied to the detection of energetic proton precipitation in association with ion-cyclotron waves ).…”

Auroral imaging from a spinning satellite

“…2,3 Later auroral imagers of increasingly greater sophistication used proper imaging cameras on missions like Viking, 4-6 Freja, 7 Polar, 8,9 and Imager for Magnetopause to Aurora Global Exploration (IMAGE). [10][11][12] It should be noted that the auroral imagers on Defense Meteorological Satellite Program (DMSP) and the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellites were nonrotating satellites and they also carried auroral scanning photometers, which produced a single map image of the aurora during each overpass. Viking, Freja, and IMAGE were rotating satellites and their imagers were mounted to look radially outwards, which allowed relatively simple rotation compensation, but it necessitated a low duty cycle and cadence due to the fact that the imagers looked at their target only for a short period during each spin cycle.…”