Over the past few years, the US Coast Guard has reported multiple episodes of GPS jamming at non-US ports, including an incident reported to the Coast Guard's Navigation Center this June that occurred on the Black Sea. South Korea has claimed on several occasions that North Korea has jammed GPS near the border, interfering with aircraft and fishing fleet navigation. And in the event of a war, it's possible that an adversary could take out GPS satellites with anti-satellite weapons or some sort of cyber-attack on a satellite network.
The risk to GPS has caused a number of countries to take a second look at terrestrial radio navigation. Today there's broad support worldwide for a new radio navigation network based on more modern technology—and the system taking the early lead for that role is eLoran. As Reuters reports, South Korea is preparing to bring back radio navigation with eLoran as a backup system for GPS, and the United States is planning to do the same.
Because it uses low-frequency radio waves (in the 90 to 110 kHz range), it's not likely that you'll see eLoran integrated into your smartphone. While the antenna required for receiving eLoran signals is relatively small (about two inches square), that's a fairly massive amount of real estate for a smartphone to dedicate to a backup navigation system. But that size could be reduced with some investment in antenna miniaturization. And while eLoran only works in two dimensions (it doesn't provide altitude data) and only works regionally (with a range of 800 miles), it has one major advantage over GPS: its powerful low-frequency signals are far less susceptible to jamming or spoofing. The signal from eLoran beacons is 1.3 million times stronger than GPS signals. A 2006 MITRE study found that attempts to jam or spoof eLoran would be highly unlikely to work.
Old school is good school!