Abstract
The SSULI (Special Sensor Ultraviolet Limb Imager) is a low-resolution hyperspectral far- and extreme-ultraviolet
limb-scanning imager designed to monitor ionospheric and thermospheric airglow. SSULI has a spectral range from 80
to 170 nm, and a nominal resolution of 2.1 nm (at 147 nm). The instrument is scheduled to fly aboard all DMSP Block
5D3 weather satellites. The first SSULI instrument was launched in fall 2003, aboard DMSP F16, and has been
collecting data since December 2003. The second SSULI flight aboard DMSP F17 began in fall 2006. On the ground,
the SSULI instruments are calibrated using a monochromator to isolate single emission features of interest produced by
a gas discharge lamp, whereas the flight spectra consists of numerous overlapping emissions. The determination of
individual emission feature contribution against the entire airglow spectrum is determined using the multiple linear
regression technique with basis functions defining each observable emission. The accuracy of the emission extraction
depends primarily on the ability to model the characteristics of the instrument line-shape, encompassing both optical
and electronic effects. In the course of developing the ground calibration algorithms, we are now able to produce line-shapes
much more faithful to the observed calibration features, as well as model instrument characteristics such as
scattered light and detector background components. This improved instrument characterization can then be passed to
the operational orbital emission extraction software to increase the fidelity of retrieved altitude profiles for observed
ultraviolet emissions. In addition, the techniques used with the ground calibration can monitor deviations in line-shape
and instrument sensitivity as a function of observed count rate, and these modified line-shapes can also be passed to the
ground analysis software. Validation of this method using SSULI 003 and 004 ground calibration data will be
presented.
