The RPI instrument is a low-power
radar which operates in the radio frequency bands which
contain the plasma resonance frequencies characteristic
of the Earth's magnetosphere (3 kHz to 3 MHz). RPI can
locate regions of various plasma densities by observing
radar echoes from the plasma that are reflected where
the radio frequency is equal to the plasma frequency.
By stepping through various frequencies for the transmitted
signal, features of various plasma densities can be
observed and, by fitting contours and/or magnetospheric
models to the features, a 3-D specification of the shape
of the magnetosphere can be created.
The RPI instrument consists of an
electronics enclosure, four 250 m wire antennae with
deployers (including switches and couplers), and a z-axis
boom canister containing two 10 m lattice boom antennae
and two preamplifiers.