A short explanation of why we need to get on with providing a terrestrial alternative to the GPS system by Dennis L. Bryant, Capt. USCG (retired).
Reportedly GPS can be spoofed for as little as $300.
With the Coast Guard’s increasing use of drones that use GPS navigation, its not unlikely drug smugglers will start spoofing GPS. We should be ready to detect such efforts and perhaps home in on them. Maybe need an inertial navigation alternative on our UAVs? (Not really sure what we are using right now.)
Chuck Hill's CG Blog 