Why Three Satellites Are Required to Detect and Geolocate GNSS Jammers from LEO

Introduction

GNSS jamming — intentional or accidental emission of broad- or narrowband interference into GNSS frequencies — threatens navigation, timing, and safety across civil and military domains. Rapid detection is crucial, but effective mitigation requires precise localization of the jammer so it can be neutralized or its effects contained.

For reliable geolocation from space, a minimum of three Low Earth Orbit (LEO) satellites is typically required. The reason is geometric: timing and frequency measurements from multiple vantage points reduce ambiguity and allow a single ground point solution.

How LEO Satellites Detect and Localize Jamming

A jammer is an RF emitter. When multiple LEO satellites receive the same interfering signal, each records slightly different arrival times and frequency offsets (Doppler). Cross-comparing these measurements yields constraints on where the emitter must be.

The three core measurement methods are:

1. TDOA – Time Difference of Arrival

TDOA measures the differences in signal arrival times across satellite receivers. Each pair of satellites defines a hyperbolic surface of possible emitter locations. With only one hyperbola, many ground points remain possible.

2. DTOA – Differential Time of Arrival

DTOA refines TDOA by taking into account GNSS waveform characteristics and correcting for propagation effects (ionospheric delay, multipath). DTOA improves the precision of the hyperbolic constraints, particularly in challenging RF environments.

3. FDOA – Frequency Difference of Arrival

LEO satellites move quickly relative to a ground emitter; this relative motion produces Doppler shifts that differ per satellite. Measuring frequency differences adds a complementary geometric constraint that helps collapse the hyperbolic solution set.

Why Three Satellites Are Necessary

• One satellite can only detect that interference is present — it cannot localize.

• Two satellites produce a locus (hyperbola) of possible emitter positions — still ambiguous.

• Three satellites provide the minimum geometric diversity: TDOA/DTOA curves intersect and FDOA constraints overlay frequency-based limits, producing a unique intersection point that identifies the jammer on the ground.

Combining time and frequency differences is especially powerful in LEO because the high orbital velocity amplifies Doppler signatures, providing strong FDOA information that complements timing-based solutions.

Conclusion

As GNSS systems underpin logistics, critical infrastructure, transport, and defense, operational resilience against jamming is essential. LEO-based multilateration using TDOA, DTOA, and FDOA provides a robust path to real-time detection and precise geolocation of jammers — the key first step to mitigation

Call to Action

We develop space-based systems for GNSS interference detection, localization, and classification from LEO. If your organization needs to harden navigation and timing capabilities against jamming, get in touch to discuss pilots, integration, or collaborative development.