Far Ultraviolet Imaging from the Image Spacecraft: 1. System Design

Abstract

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.

A superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures

“…[7] In this study we use a subset of substorms identified by Frey et al [2004] from images of the northern hemispheric auroral oval made by the far ultraviolet (FUV) instrument on board the IMAGE spacecraft [Mende et al, 2000a[Mende et al, , 2000b. The FUV instrument consisted of a wideband imaging camera (WIC), and two Spectrographic Imagers, SI12 and SI13.…”

“…The poleward edge of auroral oval emission is often used as a proxy for the location of the boundary between the more poleward open magnetic field lines and the more equatorward closed magnetic field lines, the open-closed magnetic field line boundary (OCB) [e.g., Boakes et al, 2008, and references therein]. Global hemispheric auroral imagery from orbiting spacecraft, such as the Imager for Magnetopause-toAurora Global Exploration (IMAGE) mission [Mende et al, 2000a], thus allows the size of the region enclosed by the auroral oval (the polar cap), and hence the hemispheric open magnetic flux content of the magnetosphere (F pc ), to be estimated [e.g., Milan et al, 2003Milan et al, , 2007. Several studies [e.g., Milan et al, 2003Milan et al, , 2007Milan et al, , 2009aCoumans et al, 2007;DeJong et al, 2007;Hubert et al, 2008;Boakes et al, 2009;Huang et al, 2009] have employed such methods to show that F pc typically increases by ∼25%-35% during the substorm growth phase, while the average F pc at onset is typically between 0.5 and 0.7 GWb (but can be as low as 0.3-0.45 GWb for very weak events and as high as 0.8-1.0 GWb for sawtooth events).…”

The location of the open-closed magnetic field line boundary in the dawn sector auroral ionosphere

“…In each case, the mag- netic field line footprint has been estimated using the Tsyganenko 1996 (T96) magnetic field model (Tsyganenko, 1995(Tsyganenko, , 1996, parameterised by appropriately lagged solar wind and IMF observations. Global observations of the auroral oval are provided by the Far UltraViolet (FUV) imager on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft (Mende et al, 2000a(Mende et al, , 2000bFrey et al, 2001). The FUV instrument comprises three sensors, each sensor working simultaneously over different wavelength intervals and data from two of which are presented below.…”

Observation of the proton aurora with IMAGE FUV imager and simultaneous ion flux in situ measurements

“…The IMAGE SI12 has a gorill system to reject the geocoronal Ly cx emission at 1215.6 A and allow a fraction of the broad auroral Ly cx line profile [Mende et al, 2000a[Mende et al, , 2000b. Since this emission is emitted by excited fast H atoms, the line profile for a given observation geometry depends on the energy spectrum of the incident auroral protons and their pitch angle distribution.…”