PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = "2001-08-31" NOTE = "Experiment description for the Satellite Occultation Experiment conducted starting in 1996 through 1999 (DOY 354 through DOY 259). Formatted for display or printing with up to 78 constant width characters per line." END_OBJECT = TEXT END Satellite Occultation Measurement Experiment The Radio Propagation Team (part of the Radio Science Team) conducted occultation experiments during closest approach of the orbit. The occultation experiments were done at Callisto. In general, an occultation of the Earth occurs when the spacecraft travels behind a body from the Earth's point of view (or, from the space- craft's point of view, the body "occults" the Earth). Ingress occurs when the spacecraft disappears behind the body, and egress occurs when the spacecraft reappears on the other side. Right before ingress and right after egress, the signal travels from the spacecraft to the Earth through the body's atmosphere (or ionosphere). These are the periods in which Radio Science is interested. The signal path through the atmosphere (or ionosphere) actually "bends", and a phase change is observed on the Earth. Since the spacecraft position is known, the amount of refraction caused by the atmosphere (or ionosphere) can be deduced. The amount of refractivity is plotted versus atmospheric (ionospheric) depth in a refractivity profile. The current model of the atmospheric composition (ionospheric density) of the body, which takes into account the types and behavior of the gases (electrons) is then altered to account for this refractivity profile. Vertical profiles of temperature and pressure in the atmosphere, and of electron density in the ionosphere, can be derived from the refractivity data. For the Satellite Occultation Experiment, the observation begins at 10,000 km above the Satellite and continues until ingress. The observation resumes at egress and continues until 10,000 km above the Satellite.