Physics doctoral student Panagiotis Vergados (MSc '06) has found a new technique for improving the precision of global positioning systems (GPS) dual-frequency signals – and won four national and international awards in three 
years for papers detailing how.
Vergados developed this technique to get more accurate readings of the Earth’s thermal structure.
It was designed for satellite-to-satellite GPS signals but works just as well in ground-to-satellite GPS used by the average driver.
Left: Panagiotis Vergados
Atmospheric scientists like Vergados estimate atmospheric parameters – pressure, density and temperature – by analyzing GPS signals received by low Earth-orbiting (LEO) satellites orbiting inside the Earth’s ionosphere.
As GPS signals enter the ionosphere – the Earth’s uppermost layer – on their way to the LEO satellite, the signals bend and accelerate. Scientists routinely correct for this effect when analyzing the signals for atmospheric parameters.
But they don’t bother correcting the second-order ionospheric effect – that of the Earth’s magnetic field on the GPS signal traversing the Earth's ionosphere. “It is a bit cumbersome to trace the signal and have knowledge both of the magnetic field and electron content at every point along its trajectory,” says Vergados.
No longer. The 28-year-old Vergados has found a simpler way to factor in this second-order ionospheric correction that results in more accurate atmospheric readings.
He applied the Faraday rotation phenomenon, a radio-astronomical technique used to calculate magnetic signals coming from galaxies, to resolving the second-order ionospheric correction in the GPS signals. “I said to myself, why not give it a try and maybe the Faraday would work better.” It did.
To make the Faraday technique work in retrieving more accurate atmospheric data from GPS signals, Vergados had to design three algorithms. He has presented each one in three separate and award-winning research papers, two of which have already been published in scientific journals.
“One would be good, but three is very good” for a doctoral student, says a proud Vergados, who hopes to graduate this coming academic year.
The first paper was "Bending angle retrieval algorithms using COSMIC mission observations". It won the national Best Student Paper Award in Geodesy at the Canadian Geophysical Union (CGU) conference in Banff, Alta., in 2008.
The second was “Studying the effect of GPS radio occultation bending angle variations on the retrieval process of dry atmospheric temperature profiles: A sensitivity analysis”. It won third place in the international Best Student Research Paper competition at the fourth FORMOSAT-3/COSMIC Data Users Workshop in Boulder, Colorado in 2009. (COSMIC is a constellation of six micro-satellites orbiting the Earth at about 800 kilometres)
The third was titled “A new technique in retrieving Total Electron Content and second-order ionospheric delays in radio occultation experiments using GPS”. It won two awards – CGU Best Student Paper and Best Student Paper in Geodesy – presented earlier this month in Ottawa at the 2010 Canadian Meteorological and Oceanographic Society-Canadian Geophysical Union Congress (CMOS-CGU). The congress had over 1,000 registrants, and Vergados was competing against 10 to 15 students across Canada.
Judges must have been not only impressed with the groundbreaking content but with his easy-to-understand presentation, says Vergados.
Left: Panagiotis Vergados (right) accepts his 2010 CMOS-CGU prizes, with Spiros Pagiatakis, his PhD supervisor and CGU president
“The topic is completely new and I am one of the few students in Canada who works in this kind of research.”
Not bad for a PhD student in physics who grew up in Greece and only came to Canada seven years ago.
Vergados earned a bachelor of science in physics from the University of Ioannina in Greece in 2003. At a wine and cheese reception at the university, the Canadian ambassador approached him and his friends and suggested they attend a workshop on graduate studies in Canada. For a lark, he applied to York. Meanwhile, he found a graduate position in Germany’s Max Planck Institute for Plasma Physics and planned to go to school there – until York accepted him. Before he could say no, his Canadian-born mother had packed his bags and bought him a ticket to Toronto. He could speak English and had family here.
By 2006, Vergados had a master of science. For the past four years, under the supervision of Spiros Pagiatakis, a professor of geomatics engineering in York’s Faculty of Science & Engineering, he has been working on his PhD. He expects to graduate next year and is already scouting around for a post-doc fellowship at national research centres and universities in Canada.
Vergados has no intention of returning to Greece. “I’m glad I came to York.”