Comment If you are on a large rigid vehicle... (Score 2) 108
... there are actually multiple way to spot simple spoofing.
Essentially you put multiple GPS receivers on the extreme ends of your vehicle. If spoofing is done by a single transmitter, they will all get the same position, but different times. You can detect this. If spoofing is done by multiple transmitters, each one simulating a satellite, the distances between your GPS receivers will vary widely.
So essentially you can either use timing-grade GPS receivers and compare their "PPS"-signal, or you can just take the position information from each GPS-receiver and, for example, calculate the distances of them. Those should, within error margins, never change. If there is a simple spoof, those distances will all be zero.
Since aeroplanes often have wingsspans of 10 meters or more, the precision of the GPS position signal should be good enough to determine if it is "correct" or "zero".