Interplanetary scintillation (IPS) is a phenomenon that has been known of and used as a measuring technique for nearly four decades. The aim of this thesis is to explore the practical capacity of IPS as a tool for probing the solar wind. The radio waves from distant sources (radio galaxies, quasars, etc.) must pass through the turbulent interplanetary medium (IPM) before being detected on Earth. Plasma density variations in the IPS cause scintillation of these radio waves. By careful analysis of the signal, the scintillating component can be extracted, and the amount of scintillation quantified. This relates to variations in the density of the plasma through which the radio waves have passed. The velocity of the solar wind can also be determined from IPS. By observing thousands of scintillating sources across the whole sky, an all-sky image of the solar wind can be created. Of course, scintillation can occur at any point along the line of sight to the source. Careful modeling can calculate where the dominant contribution to scintillation takes place, enabling a 3-dimensional image of plasma density to be inferred. In this thesis, a large IPS data set has been examined and evaluated, to reveal large scale structure in the inner heliosphere over a 5-year period. Chapter 1 introduces the history and theory of IPS, and the different applications to which it can be applied. The theory is first presented as a simplified approximation, and then developed to a more complex form, closer to reality. The solar wind itself is also discussed, as well as the different phenomena on the Sun that affect the properties of the solar wind. The areas of solar-terrestrial relationships and geomagnetic storms are explored. Chapter 2 focuses on the gathering of IPS information for the Cambridge 1990-94 IPS survey. The 3.6 hectare Cambridge IPS array is described, along with the observing procedure for the survey. The new computer software that processed the raw data is described and the algorithms discussed. Chapter 3 begins the task of quantifying the scintillation of each source. It examines the algorithm written to fit a template over the scintillating flux recorded for each source for every day of the survey. The density and velocity parameters computed for the whole survey are then thoroughly checked and analyzed. Finally, all sky maps are made to display the computed parameters for one day at a time. The verification of the Cambridge data set by comparison with other experimental data is the main theme of chapter 4. Measurements of plasma density and velocity taken by in- situ spacecraft are available on the Internet. Data from the IMP-8, SAMPEX and GOES satellites, from the Ulysses spacecraft and from ground-based facilities are correlated with the Cambridge data set. Though it is difficult to make direct comparisons of two different observing systems, some satisfying correlation is found. After verification of the data set, chapter 5 begins to apply this data to a number of different situations. Initially, the issue of 3-dimensional interpretation of the 2-dimensional maps is explored and modelled carefully. The trends observable over the solar cycle are then investigated, particularly those trends that depend on heliographic latitude. The ability of IPS to track large-scale structure in the IPM, and therefore to predict geomagnetic storms is also investigated in chapter 5, with some specific examples being researched. Lastly, IPS data is used to help verify the existence of a pulsar planet. Chapter 6 draws some conclusions about the research that has taken place, and the successes achieved, before giving some suggestions for improvements and future work.
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