A new open-source signal intelligence tool could help pilots and navigators avoid concentrations of GPS interference.
Guest post by Dr. Thomas Withington
Jamming satellite navigation signals is the navigator’s scourge. It’s loosely referred to as “GPS jamming,” reflecting the superiority of the United States’ Global Positioning System (GPS). However, it can affect any signals sent by satellites to aid in navigation at sea, on the ground, or in the air. The world has four Global Navigation Satellite Systems (GNSSs), as they are actually called. The GPS constellation shares space with the European Union’s Galileo, Russia’s GLONASS and China’s Beidou. All these satellites broadcast signals from the cosmos. By receiving three or more signals from different satellites, GNSS terminals calculate the location of the person, vehicle, plane or ship carrying them. It is no exaggeration to say that the world relies on GNSS signals.
The Jamming Scourge
This dependency creates vulnerabilities that have been exploited in recent years by jamming GNSS signals. Jamming comes in two forms: either blocking the signal, or hacking the signal and feeding false information. Thus, the user either receives no signal at all or receives a signal that carries misleading data.
Following Russia’s intervention in that country’s civil war beginning in 2015, large-scale GNSS clutter was detected in and around the Syrian theater of operations. In 2018, reports surfaced of GPS signal jamming attacks in Syria against unmanned aerial vehicles (UAVs) deployed by US forces deployed there. Related reports noted that GNSS interference had been detected in the Ukrainian theater of operations since 2014. Russia had invaded Ukraine in February of the same year and occupied the southern Crimean region. Examples of GNSS jamming in Ukraine included attacks on UAVs flown by the Organization for Security and Cooperation in Europe. In its own words, the OSCE was tasked with “impartially and objectively monitoring and reporting on the situation in Ukraine; and to facilitate dialogue between all parties to the crisis.” The organization had deployed Schiebel CAMCOPTER S-100 UAVs to support its mission.
Like airplanes, ships, and vehicles, UAVs use GNSS signals for navigation. All GNSS signals are transmitted on frequencies from 1.1 gigahertz/GHz to 1.6 GHz. The problem for GNSS users is that the signals have to travel thousands of kilometers from the satellites. Spacecraft are limited in the power they can put behind the signal. This is because they are limited in terms of the physical space available to house the required power generation systems. As a result, GNSS signals can be as weak as less than 50 watts when they reach Earth.
This low power level makes it relatively easy to “crowd out” the weak GNSS signal by sending a more powerful but spurious jamming signal into the GNSS terminal. This interfering signal can either be simple noise that drowns out the real signal, or an apparently correct GNSS signal that has been chopped with incorrect information. Either way, it’s bad news.
The problem for anyone using GNSS is that, until now, ordinary civilians have had difficulty obtaining information about where interference has occurred so that it can be avoided. Luckily, help is at hand. Incidents of GNSS interference are now tracked and updated daily on the GPSJam Map. The map is very intuitive. A simple red, yellow, and green color key shows the strength of GNSS interference on any given day. Green means zero to 2 percent interference, yellow means 2 to 10 percent, and red means more than 10 percent.
Where to avoid
It is perhaps not surprising that many of the red areas correlate with sensitive locations or regions affected by war or crisis. A cursory look at the August 8 map reveals instances of significant GNSS interference recorded in the eastern Mediterranean. Areas around Cyprus, Israel, Jordan, Lebanon, Syria and Turkey were particularly affected. Significant disturbances were noted farther east near Armenia and Azerbaijan, with areas south of Erbil in northern Iraq similarly affected.
Where is the blockage coming from? Russian electronic warfare equipment deployed in Syria has been blamed for some of the disruption in and around the troubled country. The Russian Army’s Zhitel R-330 system can jam GNSS signals and other transmissions on a waveband from 100 MHz to 2 GHz. The R-330 was deployed to support Russia’s intervention in Syria, primarily to jam GNSS-guided ordnance. This may have been the source of interference signals experienced in and around the Syrian theater. Likewise, the Russian government is suspected of deploying GNSS jammers at strategic locations in Moscow. That GPSJam Indeed, the map shows a high concentration of GNSS clutter in and around Moscow. Not surprisingly, strategically important military installations in and around Murmansk in the Russian Arctic are often affected by GNSS interference.
The map draws its information from GNSS interference reports compiled by the Automatic Dependent Surveillance Broadcast (ADS-B) system. ADS-B is used by aircraft to share details about their flight and identity with air traffic controllers. Information about the aircraft’s location at any given time is derived from the aircraft’s GNSS receiver. If the signal of this GNSS receiver is interrupted, the ADS-B information may be corrupted.
John Weisemannthe creator of GPSJamobtains the ADS-B data from the adsbexchange.com Website. This has raw values for ADS-B navigation uncertainty possibly caused by GPS interference. “The ADS-B exchange also does some light processing when flagging an aircraft with ‘bad GPS,'” says Mr. Wiseman. In addition, the site “attempts to filter out aircraft that just have broken equipment or a bad data point” in their ADS-B data.
At the moment the map only shows examples of GPS signal interference as used by ADS-B. However, since GPS is probably the most commonly used GNSS, the map’s data has utility beyond the aviation community. There are some parts on the map that don’t appear to have GPS interference but are known to have GPS outages. For example, there are no details about GNSS interference over Ukraine and the Black Sea, although it is reported. This lack of information is a result of the closure of Ukraine to international civil aviation. If aircraft lack ADS-B systems when flying over certain areas, they will not necessarily record GPS clutter.
That GPSJam map is a significant open source addition to our understanding of GNSS clutter. The information will be useful for navigators – especially pilots who can change their routes to avoid interference. Researchers can now record GPS interference over longer periods of time to identify trends and improve forensics into who might be responsible. In fact, Mr. Wiseman says he wants to “add an easier way to view trends, changes and anomalies over time.” The so-called Citizen’s SIGINT (Signals Intelligence) is becoming more and more popular and useful. John Wiseman’s map is an important contribution to this end.
dr Thomas Withington is an award-winning analyst and author specializing in electronic warfare, radar and military communications. He has written extensively on these subjects for a number of professional and general publications. He also works as a consultant and consultant in these areas for several leading clients in the public and private sectors. In addition, Dr. Withington regularly provides commentary on security and defense aspects of the use of the electromagnetic spectrum for major media organizations around the world. @tomwithington