Space-time localization of inner heliospheric plasma turbulence using multiple spacecraft radio links

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 1 AU 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 uplinks 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.