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.
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