My tupence worth
To clarify a few for the comment above:
- Whilst the chart shows the origin of the test out at sea, it is most likely that any jamming system would be airborne flying above the ships, therefore drastically increasing its effective range both to airborne and ground receivers.
- Differential GPS can only correct relatively small timing (clock sync) errors and atmospheric / ionospheric errors of the satellite signals by comparing the computed position to the actual known ground position. This will completely fail if there are no satellite signals to compare ie signal jamming, or if they are testing a new system which is able to induce variable unknown latencies and errors into the satellite signal.
Interestingly Cellphones and Assisted GPS receivers (AGPS) may well fair much better than DGPS and aircraft systems as they can fall back on cell tower triangulation which whilst much less accurate, is an independent system and so depending upon the durations of the disruptions and the algorithms involved in the specific receivers they may be able to maintain a rough track plot.
Of course all commercial aircraft also carry Radio Direction systems which are used for navigation so a bit of GPS disruption shouldn't affect your transatlantic flight to America.