Maritime Jamming Trial Shows GPS Vulnerabilities

Categories: GPS Vulnerability
      Date: 03/02/09
     Title: Maritime Jamming Trial Shows GPS Vulnerabilities

3.2.09 - The General Lighthouse Authorities (GLAs) of the United Kingdom and Ireland conducted a GPS jamming exercise in spring 2008 to investigate the effect of GPS service denial on maritime navigation and DGPS monitoring operations, as well as evaluate the performance of eLoran.

GPS World, March 2, 2009

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Maritime Jamming Trial Shows GPS Vulnerabilities

eLoran Shown to be 95 Percent Accurate

The General Lighthouse Authorities (GLAs) of the United Kingdom and Ireland conducted a GPS jamming exercise in spring 2008 to investigate the effect of GPS service denial on maritime navigation and DGPS monitoring operations, as well as evaluate the performance of eLoran. The exercise and its results are described in GPS Jamming Trial Summary Report (Report No. RPT-26-AJG-08) published September 23, 2008. Reprinted here is the executive summary.

Executive Summary

The GLAs worked with the UK Government's Defence Science and Technology Laboratory (DSTL) to conduct a GPS jamming exercise off the coast of Flamborough Head from the 31st March to the 4th of April 2008.

The trial was organized to investigate the effect of GPS service denial on maritime navigation, AtoN performance, and DGPS monitoring operations. The service denial of GPS also provided an excellent test environment for the development of the case for eLoran. It is important to note that the effect of GPS service denial is the same whether through intentional jamming or unintentional interference.

The trial was designed to provide:

An indication of the effect of GPS jamming on the safety of mariners'
An evaluation of how mariners cope with a sudden loss of GPS as primary navigation input;
An investigation into the performance of the GLAs DGPS service and how it is affected by GPS jamming;
An audit of how the GLAs' procedures work when a DGPS station is affected by GPS jamming
An assessment of the performance of eLoran as a backup to global navigation satellite systems (GNSS)
A trial/demonstration on which to continue and expand the case for eLoran; Ongoing receiver performance and monitoring;
An evaluation of the effect on AIS;
An evaluation of the effect on synchronised light units and systems; and
An investigation into the effect of GPS denial on communication systems used by the GLAs.

The results of the trial were:

The trial vessel was able to navigate safely during service denial periods using radar and traditional navigation techniques; however, it was not able to perform activities requiring high-accuracy positioning and it should be noted that the crew had prior knowledge of GPS failure.
The sudden loss of GPS caused many alarms to sound on the bridge. The crew on the trial vessel were expecting them to sound; however, it took several minutes to cancel alarms and continue navigating. Therefore, an unexpected GPS outage at a critical point in an operation could be distracting and hazardous.
The GLAs DGPS station at Flamborough head was significantly affected by GPS jamming. The reference station failed to receive satellite signals and set itself unmonitored rather than unhealthy. On cessation of the jamming unit, the station alarmed, went unhealthy, and then locked up, requiring human intervention and a full power cycle before recovering. This was repeated with each jamming session.
The GLAs' DGPS procedures worked well, with the monitoring officer seeking assistance from the DGPS manager when required.
eLoran's positions were recorded onboard the vessel and consistently maintained the vessel's position during GPS jamming. The position accuracy of Loran was assessed prior to the start of the jamming exercises and it was found to be on the order of 8 m (95%) in the area of Flamborough Head.
eLoran was demonstrated to the audience and showed that the vessel's position on an electronic chart was perfectly usable for coastal phase navigation during periods of GPS outage.
Three additional (D)GPS receivers were installed on the trial vessel. DGPS Receivers A and B provided erroneous data during jamming periods. These receivers reported the vessel's position up to 20+ km away from the true location, with the vessel's velocity reported as unfeasibly high. The vessel's own DGPS receiver performed similarly. DGPS Receiver C performed better and did not produce any erroneous data, although this is a more expensive unit.
The effect of GPS service denial on AIS was clearly visible. The nearby Maritime Coastguard Agency (MCA) station recorded data showing incorrect tracks of vessels with some vessels sailing over land. The AIS on the trial vessel lost range and bearing information during GPS jamming. From observing other vessels' AIS traces overlaid on the trial vessel's radar, it was clear that AIS reported positions and radar positions diverge, resulting in errors greater than 1 NM.
Synchronised lights were investigated with the conclusion that, if there is GPS service denial when they are first switched on, they will fail to synchronise. However, once synchronized, they use their internal clock. Every 20 minutes the unit attempts to resynchronise the internal clock to GPS. For the duration of the trial the lamps did not lose synchronization.
Communication systems worked continuously and showed no sign of any problems throughout the trial. It was not possible to check the performance of the Digital Selective Calling (DSC) system, although the unit alarmed during periods of jamming indicating loss of GPS. This would result in erroneous or no position information being transmitted should the DSC facility be utilized during an emergency.

The conclusions that can be drawn from the trial are:

GPS is vulnerable and this trial has investigated GPS service denial by intentional interference using low-power jammers. It should be clear that the results can be extended to GPS service denial by unintentional interference. Unintentional sources of interference include spurious harmonics from active TV antennas, damaged GPS antenna cables, and ionospheric effects. The latter are correlated with an eleven-year sunspot cycle and are particularly prevalent at high latitudes. This will bring challenges when arctic shipping routes become available.

The main conclusion from this trial is that GPS service denial has a significant impact on maritime safety:

On shore - The marine picture presented to Vessel Traffic Services/Management (VTS) will be confused as AIS information with erroneous positions and high-velocities conflicts with the radar information. Further study is needed to determine how VTS operators will respond.
AtoNs - DGPS reference stations can be jammed and the impact may results in the absence of DGPS corrections and integrity information broadcast to users over a very large geographical area; AIS used by an AtoN may broadcast incorrect information; and synchronised lights may not be synchronised, thus having an adverse impact on visual conspicuity.
On ships - Navigation, situational awareness, chart stabilization, and DSC emergency communications will be lost if they are based on GPS. Some vessels have integrated bridge systems, which enable automatic execution of a passage plan on autopilot. If this system is operating at a time when jamming occurs then, depending on the system design, the vessel's course and heading may change without informing the watchkeeper, potentially leading to extremely hazardous consequences. At this point, continuation of navigational safety is dependent on mariners' abilities to recognize that GPS service is being denied and to operate effectively using alternative techniques (e.g. radar parallel-indexing). Increased use of ECDIS will increase the attendant risks.
On people - People are conditioned to expect excellent GPS performance. As a result, when ships' crews or shore staff fail to recognise that the GPS service is being interfered with and/or there is a loss of familiarity with alternative methods of navigation or situational awareness, GPS service denial may make a significant impact on safety and security. In this trial, despite the fact that the Pole Star's crew was forewarned, problems were experienced with the ECDIS. Moreover, the number of alarms that can sound on the bridge can be distracting. Moving to other navigation techniques can cause an increase in bridge workload.

eLoran was unaffected by GPS jamming and demonstrated an accuracy of 8.1 m (95%), which is comparable to stand-alone, single-frequency GPS. Consequently, eLoran can be used to detect erroneous positions and high velocities that may be experienced during GPS service denial. Moreover, when GPS is unavailable, eLoran can provide a PNT (position, navigation, and timing) input to all maritime systems.

Finally, in the future e-Navigation environment, the combination of GPS, Galileo, and eLoran will provide robust and resilient PNT in order to reduce the impact of human error and to improve the safety, security, and protection of the marine environment.