Space-Plasma Imaging — Past, Present and Future

In 1986 Austen et al. proposed that a technique from medical imaging, tomography, could be used to image the Earth's ionosphere. Tomography was already very successful in creating images of the inside organs of human bodies by the mathematical manipulation of a series of X-ray measurements taken from multiple viewing angles around the body. The new idea was to use multiple satellite-to-ground radio signals to produce snapshots of the Earth's ionised environment. Tomography has now progressed into a technique for imaging the ionised plasma around the entire Earth. It is now feasible to create real-time movies of the ionised plasma, allowing us to watch the results of our planet's bombardment by the solar wind during events known as storms. The vision of the pioneering scientist Sir Edward V. Appleton for 'Ionospheric Weather' forecasting [1947], now a topical issue under the 'space weather' umbrella, is on the verge of being realised through new imaging-modelling approaches known as assimilation. It is becoming clear that ionospheric forecasting cannot be improved without storm warnings and consequently new research projects to link together models of the entire solar-terrestrial system, including the Sun, solar wind, magnetosphere, ionosphere and thermosphere, are now being proposed. The prospect is on the horizon of assimilating data from not just the ionosphere but the whole solar-terrestrial system to produce a real-time computer model and 'space weather' forecast. The application of tomographic imaging far beyond the ionosphere to include the whole near-Earth space plasma realm and possibly that of other planets is a likely possibility for the future.