Northern Lights threat to Sat-Nav signals
Research lead by a team at the University of Bath has shown for the first time that Sat-Nav signals can be broken up when they pass though aurora. The result is important for safety-critical systems, for example for people relying on Sat-Nav to provide accurate navigation information to automatically land aircraft. This research is published in a paper entitled ‘GPS scintillation in the high arctic associated with an auroral arc’ which appeared in the American Geophysical Union journal ‘Space Weather’ in March 2008.
Team leader Professor Cathryn Mitchell says ‘For successful research these days you can’t always follow traditional subject boundaries. The problems that we study do not always fit into neat little boxes called physics, environmental science or engineering'. This multi-disciplinary paper is a good example: Meggs, Mitchell and Smith from Bath were all involved with the deployment of specialist Sat-Nav equipment at EISCAT in Northern Scandinavia. Mitchell discovered the anomaly in the signal strength by setting up her computer to display the signals in movie form. Watson and Smith performed ray-tracing simulations to rule out the cause being local reflections from rock outcrops on the local Norwegian mountains. Mitchell then met Kintner from Cornell University at a conference and he suggested that the cause of signal loss might be the aurora. He had long been expecting that this could affect Sat-Nav signals. The other team members, Honary (Lancaster University) and Kristie (Finnish Meteorological Institute), were able to provide coincident auroral measurements over northern Scandinavia to support the hypothesis. The most compelling evidence came from the correlation between the velocity of the auroral arcs seen from the optical cameras and that measured from the spaced Sat-Nav receivers at EISCAT.
The overall project came about from an EPSRC fellowship to Mitchell to study environmental threats to Sat-Nav signals. It is that project that funded the purchase and deployment of the specialist
Sat-Nav scintillation equipment at the site of the EISCAT radars. The research council PPARC (now STFC) have played a key role here too - they funded the Lancaster University part of the research. Cathryn Mitchell says ‘ without the solar-terrestrial facilities supported by STFC and PPARC over the last few years this type of work would not be possible as we work in a complex and multidisciplinary subject. Team work is absolutely critical and so is international cooperation. Gone are the days when one big instrument answered all of our questions. The future of near-Earth space physics will continue to require many instruments and a willingness to share data internationally. This necessity to collaborate is one aspect that makes solar-terrestrial physics so enjoyable.’