ULTRAVIOLET IMAGING SPECTROMETER FOR MONITORING HIGH-LATITUDE PRECIPITATING PATTERNS

Previously flown satellite imaging experiments have demonstrated the s uitability of the VUV region for remote sensing observations of aurora l particle precipitation. In the wavelength region 120 to 145 nm, a do wnward-viewing imager is uncontaminated by Earth albedo, and in most c ases the intensity of auroral emissions is competitive with rescattere d light even during daylit conditions. These features permit quantitat ive imaging of auroral regions during day and night conditions. An ins trument was designed that has adequate wavelength resolution to separa te key spectral features and simultaneously observe the Doppler profil e of the auroral Lyman-alpha line. This instrument consists of an F3.8 Rowland circle spectrograph with a far-UV intensified CCD at the foca l plane. The spectrograph produces a 2-D spectral image where one dime nsion represents luminosity distribution and the other wavelength depe ndence. The UV intensified CCD is programmed to pick up the luminosity distribution of various key spectral regions. The entrance slit is pa rallel to the spin axis and during rotation, a complete luminosity map of the region under the satellite is recorded. The proton velocity di stribution will be studied by Doppler profile measurement of the Lyman -alpha line. A Hadamard grille is superimposed on the spectral slit an d the Lyman-alpha data are deconvolved to obtain the required waveleng th resolution.