FROM THE GROUND TO SPACE AND BACK – REMOTE SENSING OF HELIOSPHERIC STRUCTURES
The ground-based interplanetary scintillation (IPS) technique used to explore the interplanetary medium began in the early 1960’s with the advent of a large radio array constructed in Cambridge England. Within a few years, several groups around the world began studies using the IPS technique and built their own radio systems, and this included the University of California, San Diego (UCSD). However, many questions about the shapes of heliospheric structures remained from these early observations. Partly as practice for a space-based technique that could supplant IPS for heliospheric measurements, my colleagues and I began work on the Solar Mass Ejection Imager (SMEI), a space-based instrument that could view the whole sky around Earth like a coronagraph. The work to provide the best heliospheric information from this system culminated in an iterative 3-D tomographic reconstruction technique. With no space instrument to practice on before SMEI was launched, IPS data from Japanese scientists from Nagoya University ISEE (formerly STELab), Japan were available to be used in a similar way. Both SMEI, launched into space in 2003, and the Heliospheric Imagers on the STEREO spacecraft, launched in 2006, provided fine imagery of heliospheric structures in white-light. A variety of different tomographic techniques were developed to determine information from these data sets, and for SMEI this included a 3-D reconstruction analysis similar to that used for the IPS data. SMEI stopped operating in 2011. Since then, those involved in IPS have organized around a World Interplanetary Scintillation Systems (WIPSS) group to provide better ground-based analyses. The tomographic 3-D analysis, can now incorporate IPS data from different radio arrays around the world. When employing a world network of IPS data systems, not only can IPS predictions be made without observation dead times due to poor longitude coverage or system outages, but the program can itself be used to standardize IPS observations for use in other studies. These analyses promise great future advances in heliospheric research that includes world coverage from IPS, and from advanced radio arrays (LOFAR and MWA), new types of heliospheric IPS analyses, and potentially Faraday rotation measurements of interplanetary magnetic fields as they move outward from the Sun.