About SAT-JAM

Background

Many modern satellites carry a GNSS receiver, similar to the one in your phone or car, which is used to find the accurate position of the satellite as they orbit around Earth. This receiver picks up positioning signals broadcast by GNSS satellites (such as GPS) in higher orbits. These signals are faint, and can be interfered with or otherwise blocked or drowned out before they reach the receiving satellite.

In the worst case, this interference can leave a satellite unable to determine its own location. That's 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).

Since 2024, a large area over Europe has seen satellites' GNSS reception repeatedly disrupted by interference. The pattern of this interference is consistent with a ground-based interference source located somewhere in Western Russia.

GNSS Interference

GNSS interference refers to any external signal or phenomenon that degrades the quality or availability of GNSS signals. Satellites may experience several types of interference:

• Intentional Jamming: Deliberate transmission of signals designed to overpower GNSS signals.
• Unintentional Jamming: Accidental signal overlap from communication systems, radar, or equipment operating on similar frequencies.
• Atmospheric Interference: Signal degradation caused by ionospheric disturbances that attenuate the GNSS signal.
• Spoofing: Transmission of fake GNSS signals designed to deceive receivers into reporting incorrect position, velocity, or time.

SAT-JAM does not discriminate between interference sources, and maps any degradation in the GNSS-signals.

The Map

The map shows where interference is detected by the GNSS receivers on the selected satellites. It displays the fraction of observations affected by interference at each location over a rolling 30-day window. Each hexagonal cell represents a geographic area, with colors indicating the severity of interference:

• Green (0.0-0.2): Little to no interference
• Yellow (0.2-0.4): Interference some of the time
• Orange (0.4-0.6): Interference half of the time
• Red (0.6-0.8): Mostly interfered
• Dark Red (0.8-1.0): Constantly interfered

Data Sources

All data is sourced from the Copernicus Data Space Ecosystem, which provides free and open access to satellite data. Specifically, we use:

• GNSS Observations: Raw receiver independent exchange format (RINEX) observations from Sentinel satellites
• Precise Orbits: Extended Orbit File (EOF) format precise satellite position data

The map is updated whenever the newest GNSS and position data is available from the Copernicus Data Space Ecosystem. All the necessary data is usually available within a week.

GNSS measurements from new satellites are constantly being added to SAT-JAM.

Data Processing

The processing pipeline follows these steps:

1. Data Acquisition: GNSS observations and EOF position data are downloaded nightly from Copernicus.
2. Coordinate Matching: Observation timestamps are matched with interpolated satellite positions using linear interpolation.
3. Anomaly Detection: Signal strength anomalies are identified using z-score statistics (values -1σ below global mean Carrier-To-Noise-Density (C/N0) indicate interference).
4. Spatial Aggregation: Data is binned into hexagonal cells.
5. Temporal Aggregation: Results are accumulated over a 30-day rolling window.

About the Author

Kian Bostani Nezhad is a PhD student at the Technical University of Denmark (DTU) researching Space Situational Awareness. This website was developed as part of research into GNSS interference and its affect on space assets.

Contact

kbone@dtu.dk