Click to read the full Innovation article, “Recent GPS jamming in regions of geospatial conflict.”
Innovation Insights with Richard Langley
“Hey, let’s be careful out there.”
Some of us will remember that was how Sgt. Phil Esterhaus ended the morning roll call on the classic TV show “Hill Street Blues.” Although this warning was directed at police officers in carrying out their sometimes dangerous duties, it is good advice to anyone relying on GPS or any of the global navigation satellite systems (GNSS). Why? Although GPS and the other systems work very well in many environments, there are situations where the surroundings, such as those in natural and urban canyons, can block and reflect signals degrading or even denying positioning and navigation capabilities. And that’s not all. Space weather can also occasionally affect GPS and the other systems, limiting their use.
On top of such environmental concerns, we must worry about accidental and intentional disruptions of GNSS by radio frequency interference (RFI). GNSS signals received on or near Earth’s surface are fairly weak — much weaker than, say, cell phone signals — and so can be easily overpowered by nearby stronger radio signals. This is commonly referred to as jamming and there have been many instances of deliberate interference with GPS signal reception in North America and elsewhere. In fact, although its use by civilians is illegal, GPS jamming equipment is available that can stop a GPS-based tracking system from working.
On the other hand, GNSS signal jamming has become a common military tactic and its use is now widespread across the globe. While users might be aware that their navigation equipment is not working due to jamming, there is also the more insidious technique of spoofing, in which false GPS-like signals attempt to trick a receiver into using them rather than the true signals, resulting in an erroneous position report perhaps hundreds of kilometers away from the receiver’s true position.
While the use of GNSS jamming and spoofing can be detected on the ground and by aircraft overflying locations where the activity is taking place, these signals can be more comprehensively studied from space using satellites carrying receivers with appropriate spectrum coverage. In this quarter’s “Innovation” column, a researcher with NASA’s Goddard Space Flight Center reports on studies of GPS signal interference he has conducted using observations from a constellation of low-Earth orbiting (LEO) satellites that use onboard GNSS receivers to provide data for use in operational meteorology and the study of space weather and climate. However, the receivers also intercept jamming and spoofing signals as the satellites pass over conflict zones multiple times per day. It is in these zones and surrounding areas that all users relying on GNSS must be extra careful out there.