About SAT-JAM

SAT-JAM maps interference to Global Navigation Satellite System (GNSS) signals, such as GPS and Galileo, as experienced by satellites in orbit. It shows where selected Earth observation satellites have had their GNSS reception degraded, and how often.

The map is updated daily as new data is published. Because the satellite data is released with a delay, the most recent data is typically one to three weeks old, depending on the satellite. The exact period covered is shown in the legend.

Reading the Map

Each hexagon covers an area roughly 300 km across. Its color shows the fraction of the satellite's GNSS observations in that area that were flagged as affected by interference, averaged over the data period:

• Green (0.0–0.2): little or no interference
• Yellow (0.2–0.4): interference some of the time
• Orange (0.4–0.6): interference about half of the time
• Red (0.6–0.8): interference most of the time
• Dark red (0.8–1.0): interference almost all of the time

A hexagon shows where the satellite was, not where the interference comes from. The satellites fly hundres of kilometres above the ground, and from that height a ground-based transmitter can affect the receiver across a very large area. A red hexagon therefore means that a satellite passing overhead had degraded reception there. It does not necessarily mean that GNSS is jammed on the ground at that location, or that a jammer is present at that location.

Areas without hexagons either had no observations during the period, or fall below the minimum interference level chosen in Settings (0.2 by default).

Background

Many modern satellites carry a GNSS receiver, similar to the one in your phone or car, which they use to determine their own position as they orbit the Earth. The receiver picks up positioning signals broadcast by GNSS satellites in much higher orbits. These signals are faint, and can be drowned out or blocked before they reach the receiving satellite.

In the worst case, interference can leave a satellite unable to determine its own position. That is a problem for applications that depend on precise positioning, such as satellite communications (which need to point antennas accurately) and Earth observation (which needs to know exactly where its images were taken from).

Satellites passing over parts of Europe have experienced GNSS interference since at least 2021, with the largest increase in 2024. Our analysis indicates that the pattern is consistent with a ground-based source in western Russia, near the border with Ukraine.

Types of GNSS Interference

GNSS interference is any external signal or phenomenon that degrades the quality or availability of GNSS signals. The main types are:

• Intentional jamming: deliberate transmission of signals designed to overpower GNSS signals.
• Unintentional interference: accidental emissions from communication systems, radar or other equipment operating on nearby frequencies.
• Ionospheric effects: signal degradation caused by disturbances in the ionosphere, for example during space weather events.
• Spoofing: transmission of fake GNSS signals designed to make receivers report an incorrect position, velocity or time.

SAT-JAM does not distinguish between sources. It detects drops in received signal strength, so it is most sensitive to jamming-type interference. Spoofing, which often uses strong rather than weak signals, may not be detected by SAT-JAM.

Data and Method

All input data comes from the Copernicus Data Space Ecosystem, which provides free and open access to Sentinel satellite data:

• GNSS observations: receiver data from the Sentinel satellites in Receiver Independent Exchange Format (RINEX).
• Orbit data: restituted (Sentinel-1) and precise (Sentinel-2) orbit files, giving the satellite's position over time.

Every night, the processing pipeline:

1. Downloads new GNSS observations and orbit files from Copernicus.
2. Matches each observation to the satellite's position, interpolated from the orbit file.
3. Flags an observation as affected by interference when its carrier-to-noise density ratio (C/N0) is more than one standard deviation below the global mean (z-score below −1).
4. Groups the observations into hexagonal cells and calculates the fraction flagged in each cell.
5. Averages the results over a rolling window of about six weeks.

Because of the statistical threshold, a small share of observations is flagged even when no interference is present. Low values (green) should therefore be read as little or no interference rather than as exactly none.

More satellites will be added over time.

Disclaimer

SAT-JAM is a research product made available to the public free-of-charge. It is not intended for navigation, operational or safety-critical decisions.

Contains modified Copernicus Sentinel data 2026. Map data © OpenStreetMap contributors.

About the Author

Kian Bostani Nezhad is a PhD student at the Technical University of Denmark (DTU) researching Space Domain Awareness. SAT-JAM was developed as part of research into GNSS interference and its effect on space assets.

Questions and feedback are welcome at kbone@dtu.dk.