  Radio remote sensing of the heliosphere using spacecraft radio signals has
been used to study the near-sun plasma in and out of the ecliptic, close to the
sun, and on spatial and temporal scales not accessible with other techniques.
Studies of space-time variations in the inner solar wind are particularly
timely because of the desire to understand and predict space weather, which can
disturb satellites and systems at 1AU and affect human space exploration. Here
we demonstrate proof-of-concept of a new radio science application for
spacecraft radio science links. The differing transfer functions of plasma
irregularities to spacecraft radio up- and downlinks can be exploited to
localize plasma scattering along the line of sight. We demonstrate the utility
of this idea using Cassini radio data taken in 2001-2002. Under favorable
circumstances we demonstrate how this technique, unlike other remote sensing
methods, can determine center-of-scattering position to within a few
thousandths of an AU and thickness of scattering region to less than about 0.02
AU. This method, applied to large data sets and used in conjunction with other
solar remote sensing data such as white light data, has space weather
application in studies of inhomogeneity and nonstationarity in the near-sun
solar wind.
