The war in Gaza exposed Israel’s deliberate use of interference with GPS signals in the region, in order to confuse the enemy. How does the satellite navigation system work, why is it relatively easy to interfere with, and what are the solutions to counter such disruptions?
Reports of faults in the Global Positioning System (GPS) began almost immediately after the massacre carried out by Hamas terrorists in the Gaza Envelope on October 7. One week later, the IDF admitted that it was an intentional military move. On October 15, 2023, the Ha’aretz newspaper website reported that “Israeli Defence Forces have ramped up interference with the satellite navigation systems in the region in an attempt to thwart drone and unmanned aircraft attacks by Hamas and Hezbollah”.
Although most of us consider GPS navigation services an integral part of our lives, and view any disruptions in these services with frustration, none of the experts in the field were surprised by this move. Among the first to identify this interference were researchers in Tod Humphreys’ lab at the University of Texas, who have been monitoring GPS interference worldwide for many years. They reported that since the war broke out on October 7, airplanes flying over the Mediterranean Sea near Israel have disappeared from the map for several seconds multiple times. They claim that this provides clear evidence of significant premeditated actions undertaken in this region to disrupt satellite navigation systems.
This same research group has reported that the Israeli Air Force has a powerful GPS jammer that has increasingly impacted navigation signals over the past year. They have also warned that its use may impact not only the civil aviation industry but also other sectors that rely on GPS signals. According to their estimates, the source of the interference is located in an Air Force air control unit, situated on Mt. Meron, the tallest mountain in the Galilee.
Global Positioning System
The Global Positioning System, or GPS for short, was developed for the U.S. Army in the 1970s, under the name NavStar GPS. In the 1980s the system was opened to limited civilian use by the U.S. government, but it was only in the 2000s that all restrictions were removed, allowing the public full access to the signals transmitted by navigation satellites. Today, nearly all of us use GPS signals in one way or another - in smartphones, computers, cars, and more.
An informative video by the U.S. Air Force from the early days of GPS:
Nowadays the system is based on radio signals transmitted by 31 navigation satellites orbiting at a height of about 20,000 km above the Earth’s surface, completing two orbits around our planet every 24 hours. When these signals reach our GPS receivers, the devices process their information and use it to estimate our location.
For this purpose, each navigator needs to identify signals coming from at least four satellites. Each satellite records the exact time it sent the signal and its exact location along its orbital route when it transmitted the signal. To this equation, the receiver adds the time it received the signal and the speed of the radio waves, deducing from this the distance from each of the satellites. Thus, by combining the information on the times and location differences, from the signals transmitted from the four satellites, the receiver can calculate its exact position in space. A navigation device with access to a network of maps can display our precise location on a map and plan a route to our desired destination.
All the satellites in the GPS network are coordinated with each other. In contrast, the signal receivers, namely us, use cheap and unreliable equipment. Therefore, complex additional calculations are required to synchronize the receiver’s clock with the highly accurate atomic clocks on the satellites, which have a maximum deviation of only 40 nanoseconds (billionths of a second).
Each satellite transmits a binary code at several different frequencies, some of which are intended for military use only. Billions of GPS receivers are currently used by individuals, armies, companies and government agencies throughout the world. These days, such receivers are found nearly everywhere: in smartphones, of course, and also in planes, buses, ships, cruise missiles, drones, and many other devices.
GPS is not the only satellite navigation system active in the world today; its strongest competitor in the civilian market is the European Union’s Galileo System. Four other countries operate similar systems that are not accessible to the public. These include India’s IRNSS, Russia’s GLONASS, China’s BeiDou and Japan’s QZSS.
Parallel systems. GPS (left) and a combination of several systems forming the global network known as GNSS | Illustration: Oselote, Shutterstock
Ghost Caravans
It's not particularly difficult to hack into the navigation system we all so heavily rely upon. Even sophisticated military systems are not required for this. In the last decade there have been numerous instances where civil airplanes lost GPS signals just prior to landing, and their pilots were forced to land without the help of the satellite navigation system. Safety experts and aeronautical engineers who investigated these events claim that at least some of them were likely due to malicious interference. Significant disruptions of GPS signals can paralyze a range of sectors, including banks, stock exchanges, transportation services, electricity providers and more. By the same token, intentional interference with GPS signals can also provide a significant operational advantage during wartime.
The radio signals transmitted by satellites must transverse approximately 20,000 km before reaching our receivers, rendering them weak and susceptible. With the right knowledge and suitable equipment, interfering with these signals is quite easy.
One way to interfere with GPS signals is to falsify the radio signals, an action known as ‘spoofing’. Each GPS satellite transmits a unique identification code. A skilled hacker can replicate the codes of the satellites that are received within their vicinity, and produce similar signals from their own transmitter. Initially, the spoofing software that produces the false frequency must be precisely synchronized with the data transmitted by the satellite, replicating the frequency speed and waveform. If the information doesn’t match the original, the navigational control systems will promptly block the foreign information.
Now the hacker can gradually increase the intensity of the signals they’re transmitting, until the navigator locks onto them, and these replace the original, weaker signal coming from the satellite. From this point, the hacker can gradually alter the signal, providing nearby navigators with incorrect information about the satellite’s location, the speed of the radio waves, or their transmission time.
On the left: GPS interference in the Mediterranean Sea region and Europe on November 4 2022; on the right: interference in the same region on November 3rd 2023, during the Gaza war | Source: gpsjam.org, a website which monitors GPS interference worldwide.
False signals can be used for a wide range of deceptive actions on significant scales. For instance, a country can use them to mislead an enemy state tracking the movements of its troops. In this way, it is possible, among other things, to create the illusion of a ghost convoy of military forces that doesn’t actually exist, by intentional interference with GPS signals.
Another way to interfere with the system is to block the GPS signals, an action known as signal jamming. Since the satellite signals travel a large distance and weaken along the way, it is possible to use Earth-based transmitters that emit powerful scrambled signals at the same frequency. This can produce misleading radio noise, making it difficult for navigators to detect the satellite signals.
In contrast to false signals, blocking signals do not need to be sophisticated, but rather, strong and numerous, and of course they must be transmitted in the region designated for interference with GPS reception. Powerful radio transmitters can disrupt signals within several kilometers away.
Where Does the Noise Come From?
In April 2023, Humphreys and his colleague, Zachary Clements, in collaboration with Patrick Ellis from Spire Global, which operates a large low-orbit satellite array, published a research study on GPS interference. They showed that it is possible to detect the sources of strong GPS interference centers using data received from satellites.
Low orbit satellites, up to 2,000 kilometers, have several significant advantages. First, they are very fast and usually complete an orbit of the Earth in just 90 minutes. Thus, they can collect a large amount of information within a short time. Furthermore, due to their relative proximity to the surface they can easily receive both the GPS signals coming from the navigation satellites orbiting above them, and similar signals coming from transmitters on the Earth’s surface. Thus, they can detect unusual signals from below that hint at an attempt to falsify GPS signals or interfere with their reception.
The researchers used two methods to detect active GPS interference centers - direct reading of the signals received by the satellites and indirect interpretation of the signal source via the Doppler effect. The latter method is based on the fact that waves, such as radio waves, are compressed when they approach an object, or when an object approaches them, such that their frequency increases, and they spread when moving away from it, such that their frequency decreases. With respect to sound waves, for example, the Doppler effect is easily noticeable when an ambulance passes by - as it approaches its siren is heard at a high pitch, and as soon as it passes by and begins to move away, the frequency of the sound we hear changes and we hear a lower pitch.
A satellite at low orbit can detect the change occurring in the frequency of the GPS-interfering radio waves at the time it receives the misleading signals below it. Thus, precise measurement of the changes in the frequency of the waves should allow detection of the transmission source.
In practice, it turned out that direct examination of the signals provided more accurate, unambiguous data than that obtained from Doppler effect measurements. Based on this, the researchers identified, among other things, an Israeli interference center estimated to be located on Mt. Meron in the Galilee. Other interference centers were also identified in Ukraine, Syria, Turkey, and Iraq.
Alongside the military advantages inherent in their ability to mislead the enemy or impact its ability to operate guided munitions, GPS interference may also impact routine civilian activities. Last year, Israeli farmers already expressed complaints about the damage these interferences caused to the functioning of their GPS-based precise irrigation systems. Similar complaints have been voiced by professional drone operators, and it seems that the interference also impacts the movement of civilian airplanes in Israel’s vicinity.
Caption: Centers of GPS signal interference operating in Israel (on the right) and Ukraine (on the left), according to researchers from the University of Texas | Source: the research paper by Clements, Humphreys and Ellis
Despite the relative ease of disrupting GPS signals, there exist numerous ways to counteract such interferences. Several companies and government agencies are already using technologies designed to filter out such false signals, and more technologies are currently under development.
There are many strategies for monitoring signals and preventing disruptions. Armies, for example, use encrypted GPS signals, which reduce the risk of a hostile party falsifying their GPS signals. Some navigators also use alternative satellite navigation systems, such as Galileo, allowing them to cross-reference signals from several sources. At sensitive locations and high-security areas it is possible to install a network of antennae that can receive the radio waves and analyze their source, in order to detect unauthorized signals and filter them out.
More and more countries are now using their own ground navigation systems as an alternative and backup to the satellite GPS. These systems are based on an array of antennae and ground relay stations that transmit strong radio waves at low frequency that are difficult to block or falsify. In the event of an extensive attack on the GPS signals, cross-referencing of information from a number of antennae allows these same tailored navigation devices to detect their precise location, similar to satellite-based systems.
Futuristic Navigation Technologies
In March 2021 a new center for advanced navigation technology research was inaugurated in Israel; established by the Directorate of Defense Research and Development at the Ministry of Defense (DDR&D) in collaboration with Israel Aerospace Industries. Its main objective is to develop a non-GPS based navigation system. The official announcement about the project highlighted its intention to develop “precise inertial indices”, in other words, a system that measures, on three axes, the acceleration of the body on which it is installed and the rate of change of its direction of inclination relative to those axes. Thus, if we know the initial location, speed and direction of the body, we can accurately estimate its location, speed and direction of movement at any given moment. This calculation may also include measures of additional indices, such as the magnetic field that acts similar to a compass to detect direction, or air pressure that can facilitate altitude determination. Such systems are already in use in ships, airplanes, submarines, and spaceships; the aim is to refine them even further.
A short while later, in October 2021,Israel Aerospace Industries announced that the ADA system, which it developed to block false GPS signals “had been integrated into advanced systems of the Israeli Air Force, including F-16 airplanes and other aircraft”, and proved its capabilities during operation “Guardian of the Walls”. The system is based on a multichannel antenna that can filter out signals coming from undesirable directions—for example, ground transmitters, without disrupting the continuity of the original signals.
These are just a few examples. Technologies for interfering with satellite navigation signals and blocking this interference will continue to develop, while our dependence on GPS systems, which are now integrated into almost every facet of our lives, will surely continue to grow. As long as Israel continues to interfere with these signals for defense purposes in the hostile environment in which it is situated, there will also be an increasing need for civil sectors in Israel to seek technological means that enable them to minimize these interferences as much as possible.
Promotional video of the Israel Aerospace Industries’ ADA system