Data from millions of phones has helped produce the most complete map ever made of the ionosphere, part of Earth’s upper atmosphere. This could help us understand disturbances caused by geomagnetic storms and perhaps even improve GPS.
“Smartphone-based measurements cover twice as much of the ionosphere as traditional scientific monitoring stations,” says at Google Research. “It’s like there is a scientific monitoring station in every city where there are phones.”
Williams and his colleagues analysed data from 40 million Android phones to calculate how the ionosphere’s charged particles affect the time it takes for radio signals to travel between each phone and GPS satellites in orbit. This was previously considered impractical because phone-based measurements can be 30 times noisier than signal data from dedicated GPS monitoring stations.
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To solve this, the researchers combined measurements from the millions of phones to produce a clearer overall map of ionospheric conditions, while also accounting for the smaller antennae and less sophisticated GPS hardware in each phone.
Google already plans to use this method to improve the accuracy of GPS location-based services for Android phone users – possibly reducing location errors by several metres. Those improvements could also prove beneficial for driverless cars that rely heavily on GPS, says at National Cheng Kung University in Taiwan.
Continuous monitoring of the ionosphere using phone-based data may also help with short-term forecasting for solar storms and similar space weather events, says Williams. A baseline for this was developed in part in May, when the system was used to measure the effects of a geomagnetic storm that struck Earth.
The mapping also revealed ionospheric phenomena called plasma bubbles – which can interfere with radio communication and satellite navigation – over South Asia. These weren’t captured by the few available monitoring stations in the area.
Researchers have previously used ionospheric monitoring to track disturbances caused by major volcanic eruptions, earthquakes, tsunamis and even rocket or missile launches. But Williams cautioned that measuring smaller ionospheric changes from such events would still require the precision of scientific monitoring stations.
The new method currently requires regions with widespread cell phone coverage, which leaves out oceans and certain sparsely inhabited places, says  at NORSAR, a seismic research foundation in Norway. But he welcomed the overall improvement in coverage of ionospheric disturbances. Lin says he hopes such monitoring is extended.
“If researchers can further map the ionosphere using cell phones of the passengers on airlines or ferries, we can even fill the gap of the missing data over oceans,” says Lin.
Nature
