Method and device for detecting a decoy operation of a GNSS system

A method of detecting an operation to spoof a first satellite signal positioning device carried by a first vehicle moving in a zone in which at least one second vehicle carrying a second satellite signal positioning device is also moving, the method comprising:

• causing at least one first positioning value to be calculated for each vehicle from initial satellite signals received by each satellite signal positioning device;
• in parallel both with receiving initial satellite signals by the second satellite signal positioning device and also with calculating the first positioning value for the second vehicle, causing the second satellite signal positioning device to initiate a latching stage in order to make a new search for satellite signals and using new satellite signals received by the second satellite signal positioning device to calculate a second positioning value for the second vehicle at the same instant as the first value;
• comparing the first and second positioning values relating to the second vehicle;
• and
• issuing a warning when the two positioning values do not coincide;
• at least the second satellite signal positioning device having at least first satellite signal reception channels and second satellite signal reception channels and at least one processor unit arranged:
• during a latching mode to select transmitters of satellite signals on the first channels that are sufficiently powerful to be used, and during an operating mode that lasts for as long as the signals transmitted by the selected transmitters are sufficiently powerful, to calculate successive first positioning values from said signals;
• and
• during a latching mode to select transmitters of signals on the second channels that are sufficiently powerful to be used, and during an operating mode, to calculate at least one second positioning value from said signals, the processor unit returning automatically to latching mode after calculating said at least one positioning value on the second channels regardless of the power of the signals.