FUV airglow and aurora observation on STSAT-1

Abstract

In this study, Far Ultraviolet (FUV) observations and studies of airglow and aurora measured on STSAT-1 are presented. Traveling in a sun-synchronous orbit at 680 km altitude, STSAT-1, the first Korean scientific satellite, is equipped with a main instrumental spectrograph FIMS and a plasma detector assembly SPP. The observations were made from November 2003 to May 2005 for astronomical targets such as the interstellar medium from supernova remnants and FUV emissions from Earth`s upper atmosphere. Airglow observations have been made with several modes depending on the specific scientific purposes. Early airglow observation was used for spectral calibration and background line identification. The spectral accuracy was improved by more than 10 % by a line calibration task. Limb scanning observation for dayglow showed altitudinal line variation of dayglow emission, and the finding was compared to modeling results from AURIC. The variation trend is similar but the maximum altitude is slightly different, attributable to geometric differences. A nightglow analysis was performed for the latitudinal distribution about the equatorial and mid-latitude regions. Equatorial nightglow is comprised of atomic oxygen recombination lines. Total intensity variation of the equatorial nightglow shows that the equatorial trough structure strongly depends on the longitudinal location. The mid-latitudinal analysis exhibits high level background near the southern middle latitude region and only a mixture of 1026 $\Aring$ and OI 1356 $\Aring$ are detected. STSAT-1 also observed simultaneous FUV spectra of diffuse and discrete auroras, as well as the energy and flux of precipitating electrons measured on the same spacecraft. An FUV spectrograph image with $2km \times 3km$ resolution shows detailed small-scale features embedded in the auroral arcs. The peak energies of the inverted-V events were compared with the corresponding FUV spectra. It was found that the long band $N_2$ LBH emi...