Visualization and Analysis of Spectrograph-mode Data Products from Far Ultraviolet Scanning Imaging Sensors

Far Ultraviolet Scanning Imaging Sensors such as GUVI (one of four instruments on NASA's TIMED spacecraft) and the SSUSI instruments (on the newer DMSP satellites) typically operate in "imaging mode", wherein they gather data from a large spatial area, using a scanning mirror to image locations from the top of the limb down and across the disk. In this mode, the instruments generate only limited spectral information, which is compressed on board into five spectral "colors" that capture the most aeronomically relevant emissions. Telemetry bandwidth limitations preclude the transmission of complete spectral information at each observed spatial position (>2000 spatial positions per scan, 3-4 scans per minute). These instruments can also operate in a "spectrograph mode", wherein the full spectrum observed by the instrument is preserved, but observations are made at only a single mirror scan position. Spectrograph mode operation essentially trades spatial coverage for spectral coverage within the given bandwidth constraints. Spectrograph mode data is used for calibration purposes (e.g., stellar observations on the limb, analysis of instrument performance on the disk), but also presents some unique new scientific opportunities. The recent demise of the scan motor mechanism in the GUVI instrument (still operating long after the completion of the standard mission) means that GUVI is now operating continuously in spectrograph mode. To use these data effectively, we must generate products that distill vast quantities of data into useful and usable knowledge. We examine the state of data products associated with spectrograph mode observations, their use as a replacement for earlier imaging mode products, and potential new uses for both current and future products with enhanced spectral resolution.