How satellites help us navigate

”Have you ever encountered a situation where you did not know exactly where you are? Somewhere in the middle of nowhere and with no idea where to go? Fortunately, there was your mobile phone nearby, your small, precious device. Soon you were able to find your way out, fix yourself some decent transport, get some food, and more. And all because of the Global Navigation Satellite System, a system which we use on a daily basis and for many different purposes.”

With these words begins a new animated video that Grzegorz Klopotek, Ph.D. student at Onsala Space Observatory, has created. 

Grzegorz works with radio telescopes and space geodesy, and among other things, technology for Onsala Space Observatory's Twin Telescopes. On April 17 he defends his doctoral dissertation. In the video he explains how satellites in space help us with navigation and positioning in everyday life. How can you use your cellphone to find your way home when you get lost? ​


Why did you produce this video? 


- All Ph.D. students at Chalmers have to give a popular science presentation, before they can defend their thesis. Due to the Covid-19 outbreak, there was no possibility to prepare a normal presentation with an audience. So making a film that could reach the public sounded like a good alternative.


Who should watch the video and how can it be of use to them? 


– In principle it’s for anyone who uses smartphones and who would like to know a bit more about how global navigation satellite systems work. It’s true that these systems are used most often for navigation, but they also have other applications, for example in land surveying or in Earth sciences. With the help of GNSS satellites in space, one can measure long-term changes in climate and environment, and their variation in time and space. 


At Onsala Space Observatory, Grzegorz and his colleagues study the shape, orientation and size of the Earth using space geodetic techniques such as GNSS. They also use geodetic very-long-baseline interferometry (VLBI), which involves observing radio waves from distant galaxies (so-called quasars) with networks of radio telescopes. Together with observations of geodetic satellites, these measurements can be used to study the Earth, and how its atmosphere, sea level and climate change over different timescales.


– Space-geodetic techniques, such as GNSS and geodetic VLBI, provide us also with accurate and stable global reference frames. Those reference frames are needed in order to be able to measure, describe and quantify long-term changes in climate and the environment. You can say that with space-geodetic techniques we look deep into the sky in order to find out what’s beneath our feet.


Besides navigation, the global satellite systems have many scientific applications, Grzegorz explains.


– GNSS is used for instance to examine one of the Earth’s orientation parameters – so-called ’polar motion’ - and how the Earth’s shape is changing, for example movement of tectonic plates or land uplift. In Scandinavia, the biggest contribution to the land uplift comes from the phenomenon referred to as the post-glacial rebound. This effect is caused by the Earth’s crust returning to a mechanical resting state after being released from pressure from ice sheets during the last glacial period. With GNSS we can also study the atmosphere, particularly the troposphere and ionosphere. 


– At Onsala Space Observatory the technique called GNSS-R (GNSS-Reflectometry) is also used to determine sea-level height with few-centimeter-level precision. 


In the video you mention that there will be even more applications for GNSS in the future. Which do you think will be the next applications we can expect? 


– Autonomous driving could be the first and most obvious example. And in the near future, we can expect even better performance from GNSS for navigation purposes. 


You will defend your Ph.D. thesis on April 17. What’s next for you? 


– Probably research related not only to geodetic VLBI, but to space-geodetic techniques in general. A project concerning GNSS, satellite/lunar laser ranging and geodetic VLBI would sound good to me...


Read Grzegorz’s thesis: Observations of Artificial Radio Sources within the Framework of Geodetic Very Long Baseline Interferometry here


See Grzegorz’s film Navigation in your hand on YouTube, (subtitles are available in English and Swedish).


Published: Thu 16 Apr 2020.