The GLAs conducted a trial in 2008 on the effect of GPS service denial on marine aids to navigation, and ship-borne and shore-based navigation and information systems. The above video is of subsequent similar trials undertaken in 2009.
During the 2008 trial, a GLA vessel was fitted with two typical marine-grade DGPS receivers, a survey-grade GPS receiver, and an eLoran Receiver. The UK Ministry of Defence assisted in the trial by providing and operating a GPS jamming unit with an effective radiated power of 1.5W. The trial vessel made several runs between two way-points near Flamborough Head on the East coast of the United Kingdom.
Google Earth plot showing reported position from one of the GPS receiver during a passage through the jamming zone. Highlighted is a comparison of the worst-case GPS position (red circle) with the corresponding eLoran position (green square). Colours indicate reported speed: blue <15knots, yellow <50knots, orange <100knots and red >100knots.
The above figure shows the resulting positions recorded from one of the typical marine grade DGPS receivers are the vessel steamed from through the jamming signal. Each position is colour coded depending on the reported speed and it should be noted that all of these positions have been declared valid by the receiver. The two highlighted locations are for the same epoch and show how the GPS jamming signal has resulted in the GPS position being calculated some 22km further west than the true position calculated using eLoran.
The jamming trial was also able to show the true benefits of eLoran as a complimentary system to GNSS. Due to the different failure modes, eLoran was able to provide a navigable service throughout the jamming trial providing positional accuracy in the order of 8 metres (95%).
The GLAs plan to investigate GNSS vulnerabilities with further trials.
PDF: GPS Jamming Executive Summary
The GLAs recommend mariners do not rely on any single means of navigation, positioning or timing, but rather use all means available
