Visiting researchers team up with Clemson to study eclipse effects on GPS
CLEMSON, South Carolina – Researchers will be at Clemson University Monday to find out how the solar eclipse might interfere with GPS capabilities.
GPS, or the Global Positioning System, is a United States-owned technology that uses 24 outer space satellites to transmit signals for positioning and navigation information here on earth. Americans use it primarily to get from point A to B, but few know that GPS controls banking systems, power grids and even stock markets.
The researchers from Embry-Riddle Aeronautical University (ERAU) include Principal investigator Kshitija Deshpande and undergraduate student Nicolas Gachancipa. They will use a GPS antenna on top of Kinard Hall to monitor the ionosphere, the layer of Earth’s atmosphere that is charged by solar and cosmic radiation.
The project stems from Deshpande’s connection with John Meriwether and Gerald Lehmacher, two Clemson University professors who study atmospheric and space physics in the department of physics and astronomy.
“The main goal of our project is to see how the ionosphere behaves with different natural phenomena, like thunderstorms and hurricanes,” Gachancipa said. “Embry-Riddle is in Daytona Beach, Florida, where thunderstorms and hurricanes happen often, so those were the two main interests we had. Then, we saw that the eclipse was coming and realized it was a big opportunity for our study. Solar eclipses don’t happen in the same place very often; usually you’d have to travel to places other than the mainland U.S. to see them. So this is very fortunate for us.”
Gachancipa will track scintillation, or the amount of deflection that occurs when GPS signals try to pass through the ionosphere.
As they are transmitted to receivers on Earth, GPS signals interact with free-floating electrons that were once attached to atoms such as helium. When the sun is shining, its energetic ultraviolet radiation ionizes the helium atoms, forcing electrons to break off and become free, increasing the number the GPS signals have to bypass to reach Earth.
At nighttime the levels of radiation in the ionosphere weaken, causing the free electrons to reattach to the atoms. The number of free electrons decreases and allows GPS signals to pass more easily.
“What we’re studying here is how the atmosphere behaves during an eclipse. Do those scintillation values go up or down depending on the position of the moon and the sun?” Gachancipa said.
The expectation of ionospheric scientists like Gachancipa and Lehmacher is that 60 percent of free electrons in the ionosphere will disappear in the shadow of the moon during the eclipse.
“Normally, free electrons disappear because the Earth is rotating, causing nighttime. But this time it will happen because something – the moon – is in between the Earth and the sun, blocking the radiation that would usually heat up the ionosphere,” Gachancipa said. “It’s basically like a small nighttime during the day, except there will be very rapid and dramatic changes.”
Lehmacher and Gachancipa installed a GPS antenna on the roof of Kinard Hall that connects to a receiver inside the building. The receiver’s job is to measure every satellite in the three main constellations of outer space: GPS, from the United States; GLONASS, from Russia; and Galileo, from the European Union. Not only will it track scintillation values, but the receiver will also collect measurements of electrons in the ionosphere.
“This specific receiver measures frequently to get a much more detailed look at the ionosphere – every satellite, at 50 times per second,” Lehmacher said.
He went on to note the importance of accounting for changes to the ionosphere when calculating GPS coordinates.
“I always find it interesting that, if one did not include the signal delay caused by the ionosphere in the calculation for GPS positions, then every position would be about 40 meters wrong. That means every car, every truck, every destination would be 40 meters off,” Lehmacher said.
“It’s not only a location bias, but also a time bias,” Gachancipa added. “For example, banking systems depend on the exact timing that GPS systems provide to them. If there’s a big change in the ionosphere that could block the signals and send wrong information to banks, that would have huge consequences for them. It won’t provide the exact time of day. So our study wants to see how natural behaviors, like this eclipse, can affect the proper functioning of satellite systems and navigation systems, specifically.”