The Ionospheric Spectroscopy and Atmospheric Chemistry (ISAAC) experiment on the Advanced Research and Global Observing Satellite (ARGOS):: Quick look results

The Ionospheric Spectroscopy And Atmospheric Chemistry (ISAAC) Experiment is a high resolution mid-ultraviolet Ebert-Fastie spectrograph that is flying on the USAF Advanced Research and Global Observing Satellite (ARGOS, launched 23 February 1999). The instrument is designed to spectrally resolve the rotational structure of the nitric oxide bands, which will be used to infer the temperature in the lower thermosphere (90-200 km altitude range). The instrument is operated as a limb imager with a limb scan occurring every 100 seconds throughout the expected three year mission life. The ARGOS is in a sun-synchronous, near-polar orbit at 833 km altitude with an ascending node crossing time of 2:30 PM. The ISAAC instrument is composed of a 1/8 m focal length Ebert-Fastie spectrograph with an intensified plasma coupled device (PCD) detector. The instrument uses a 3600 l/mm diffraction grating. The ISAAC covers 400 Angstrom overlapping segments of the 1800-3300 Angstrom passband at better than 4 Angstrom spectral resolution. A stepper motor drive with a 4 position cam assembly is used to tilt the grating and select the instantaneous passband. The spectrograph is fed by a 1/8 m focal length off-axis parabola telescope. Its field-of-view is 0.03 degrees x 1.1 degrees, which corresponds to 1.5 km (vertical) x 55 km (along the horizon) projected to the limb. We will present an overview of the instrument and discuss its calibration and in-flight performance.