SPECIAL SENSOR ULTRAVIOLET LIMB IMAGER - AN IONOSPHERIC AND NEUTRAL DENSITY PROFILER FOR THE DEFENSE-METEOROLOGICAL-SATELLITE-PROGRAM SATELLITES

The Naval Research Laboratory is developing a series of far- and extre me-ultraviolet spectrographs (800 to 1700 Angstrom) to measure altitud e profiles of the ionospheric and thermospheric airglow from the U.S. Air Force Defense Meteorological Satellite Program's Block 5D3 satelli tes. These spectrographs, which comprise the Special Sensor Ultraviole t Limb Imager (SSULI), use a near-Wadsworth optical configuration with a mechanical grid collimator, concave grating, and linear array detec tor. To image the limb, SSULI employs a rotating planar SIC mirror tha t sweeps the field of view perpendicular to the limb of the Earth. in the primary operating mode, the mirror sweeps the instrument field of view through 17 deg to view tangent heights from about 50 to 750 km. T he SSULI detectors use microchannel plate intensification and wedge-an d-strip decoding anodes to resolve 256 pixels in wavelength dispersion . The detector is windowless and uses an o-ring sealed door to protect the CsI photocathode from exposure prior to insertion in orbit. The a ltitude distributions of the airglow measured by the SSULI sensors wil l be used to infer the altitude distributions of electrons and neutral species. At night, electron densities will be determined by measureme nt of ion recombination nightglow. Daytime electron densities will be obtained from measurements of multiple resonant scattering of O+ 834-A ngstrom radiation produced primarily by photoionization excitation of atomic oxygen. Dayside neutral densities and temperatures will be infe rred from the measurement of dayglow emissions from N-2 and O produced by photoelectron impact excitation.