The effect of navigation apps drifting off course may be caused by a region 50-200 miles overhead called the ionosphere, which is a region of the Earth’s atmosphere that is responsible for such drifts. There are various levels of free electrons in this layer that, under certain conditions, can be extremely concentrated, thereby slowing down the processing of GPS signals when they are travelling between satellites and devices.
A delay, like a delay that would occur from navigating through a crowded city street without being able to get to your place of work on time, is a major contributor to navigation system errors.
As reported in Nature this week, a team of Google researchers demonstrated they had been able to use GPS signal measurements collected from millions of anonymous Android mobile devices to map the ionosphere by using GPS data from those devices.
There are several reasons why a single mobile device signal cannot tell researchers so much about the ionosphere with only one device, but this problem is minimized when there are many other devices to compare with. Finally, the researchers have been able to use the vast network of Android phones to map out the ionosphere in an extremely precise way, matching or exceeding the accuracy of monitoring stations, using the huge network of Android phones. This technique was far more accurate in areas like India and Central Africa, compared to the accuracy of listening stations alone, where the Android technique was used.
The total electron content (TEC) referred to as ionospheric traffic is a measure of the number of electrons in the ionosphere used within a cellular telephone network. Satellites and ground stations are used to measure this amount of electrons in the ionosphere. These detection tools are indeed effective, but they are also relatively expensive and difficult to build and maintain, which means that they are not used as commonly in developing regions of the world.
The fact that monitoring stations are not accessible equally leads to disparities in the accuracy of the global ionospheric maps.
However, Google researchers did not address one issue. They chose to use something that more than half of the world's population already possessed: mobile phones.
In an interview with Popular Science, Google researcher Brian Williams discussed how changes in the ionosphere have been hindering GPS capabilities when working on Android products.
If the ionosphere were to change shortly, this may undermine GPS capabilities. Aside from contributing to scientific advances, he sees this project as an opportunity to improve accuracy and provide a more useful service to mobile device users regularly.
Rather than considering ionosphere interference with GPS positioning as an obstacle, the right thing to do is to flip the idea and imagine that GPS receiver is an instrument to measure the ionosphere, not as an obstacle," Williams commented.
The ionosphere can be seen in a completely different light by combining the measurements made by millions of phones, as compared to what would otherwise be possible."
Thousands of Android phones, already known as 'distributed sensor networks', have become a part of the internet.
GPS receivers are integrated into most smartphones to measure radio signals beamed from satellites orbiting approximately 1,200 miles above us in medium Earth orbit (MEO).
A receiver determines your location by calculating the distance from yourself to the satellite and then using the distance to locate you, with an accuracy of approximately 15 feet. The ionosphere acts as a barrier that prevents these signals from travelling normally through space until they reach the Earth. In terms of GPS accuracy errors, many factors contribute to the GPS measurement error, including variables like the season, time of day, and distance from the equator, all of which can affect the quality of the GPS measurement.
There is usually a correctional model built into most phone receivers that can be used to reduce the estimated error by around half, usually because these receivers provide a correctional model.
Google researchers wanted to see if measurements taken from receivers that are built into Android smartphones could replicate the ionosphere mapping process that takes place in more advanced monitoring stations by combining measurements taken directly from the phone.
There is no doubt that monitoring stations have a clear advantage over mobile phones in terms of value per pound. The first difference between mobile phones and cellular phones is that cellular phones have much larger antennas. Also, the fact that they sit under clear open skies makes them a much better choice than mobile phones, which are often obscured by urban buildings or the pockets of the user's jeans.
In addition, every single phone has a customized measurement bias that can be off by several microseconds depending on the phone. Even so, there is no denying the fact that the sheer number of phones makes up for what they are lacking in individual complexity.
As well as these very immediate benefits, the Android ionosphere maps are also able to provide other less immediate benefits. According to the researchers, analyzing Android receiving measurements revealed that they could detect a signal of electromagnetic activity that matched a pair of powerful solar storms that had occurred earlier this year.
According to the researchers, one storm occurred in North America between May 10 and 11, 2024. During the time of the peak activity, the ionosphere of that area was measured by smartphones and it showed a clear spike in activity followed by a quick depletion once again.
The study highlights that while monitoring stations detected the storm, phone-based measurements of the ionosphere in regions lacking such stations could provide critical insights into solar storms and geomagnetic activity that might otherwise go unnoticed. This additional data offers a valuable opportunity for scientists to enhance their understanding of these atmospheric phenomena and improve preparation and response strategies for potentially hazardous events.
According to Williams, the ionosphere maps generated using phone-based measurements reveal dynamics in certain locations with a level of detail previously unattainable. This advanced perspective could significantly aid scientific efforts to understand the impact of geomagnetic storms on the ionosphere.
By integrating data from mobile devices, researchers can bridge gaps left by traditional monitoring methods, offering a more comprehensive understanding of the ionosphere’s behaviour. This approach not only paves the way for advancements in atmospheric science but also strengthens humanity’s ability to anticipate and mitigate the effects of geomagnetic disturbances, fostering greater resilience against these natural occurrences.
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