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How Trimble IonoGuard Secures GNSS Precision Amid Rising Solar Activity

It's widely understood that the Earth's atmosphere directly influences the reception of GNSS signals by GNSS receivers on the ground, but are you aware that the sun significantly affects GNSS signal stability as well?

Solar activity peaks every 11 years, with the next maximum peak predicted in 2025. This has a direct impact on delays and stability of GNSS signals and can have a negative effect on precision positioning. We will explore the challenges facing GNSS users and how Trimble® IonoGuard™ technology mitigates these effects in GNSS receivers enabled with the Trimble ProPoint® GNSS processing engine.

Mitigating future ionospheric disturbances with IonoGuard

High-precision GNSS users are familiar with position degradation from ionospheric disturbances. The last solar cycle, which peaked in 2014, was a relatively mild cycle compared to the recent historical record. Understanding that future cycles may not be as moderate or geographically constrained, Trimble embarked on a data collection and development exercise early in the current cycle to ensure that our hardware and software was ready to mitigate disturbance from solar activity and maximize our customers’ productivity. The result is Trimble IonoGuard technology.


So, how does the ionosphere affect GNSS positioning and how is Trimble IonoGuard being used in the field today to optimize accuracy, availability and integrity in critical applications? The following are the different types of ionospheric disturbances and their effect on GNSS signals.

1. Solar Cycle

Sunspots are temporary areas on the sun where the magnetic field is about 2,500 times stronger than Earth's, much higher than anywhere else on the sun, lasting a few days to a few months. The more sunspots in any given area on the sun, the greater the magnetic activity. These areas can eject particles into space, which add to the solar wind and may be carried to Earth.

When more particles hit Earth, the layer of atmosphere known as the ionosphere becomes more charged, leading to an increase in GNSS signal delays from the ionosphere. The sun’s magnetic field flips once every 11 years and sunspot activity is correlated with this 11-year cycle. It is difficult to predict the magnitude of the solar cycle, however, new models and measurements indicate a cycle in 2025 similar to the cycle that peaked around 2002.


 2. Ionosphere 

The ionosphere is an ionized layer of the upper atmosphere (between 80 and 600 km above Earth’s surface, on the edge of space) that has a large number of electrically charged atoms and molecules that cause a delay in the GNSS signals that pass through it. The ionosphere varies over time, with significant differences between night and day when the solar energy source is or is not as present. 

The impact on radio waves is dependent on frequency. The delay is inversely proportional to the square of the frequency, for example, the L1 signal (at a higher frequency) has less delay than the L2 signal. A common metric describing the ionosphere is Total Electron Content (or TEC). This is the total number of electrons between two points in a straight line, e.g. between a receiver on the ground to the satellite in space. The units are electrons, per meter, squared; with the frequency of a signal, this can be converted to an equivalent signal delay.

The delay through the ionosphere is not fixed and will change based on the time of day, year and location. The elevation angle between the receiver and satellite also impacts the magnitude of the delay. A high-elevation signal will take the shortest path through the ionospheric layer of the atmosphere as the path is perpendicular to the ionosphere. A low-elevation signal will pass through the ionosphere at an angle and experience a much higher delay. Peak delays tend to be in the early afternoon, with lower delays overnight.

3. Equatorial Effects

During the evening hours around the equator, plasma rises in the ionosphere. This can lead to instability within the ionosphere and results in scintillation. This is an effect where the GNSS signals are impacted by varying electron densities in the ionosphere, which can result in very rapid phase and amplitude change, leading to poor tracking, complete loss of lock, and/or carrier phase cycle slips. When the instability occurs, it may be limited to certain regions or bubbles of the ionosphere and only a subset of satellites may be affected. It also follows an annual cycle, with most disturbance between September and March and severity dependent on the 11-year solar cycle.

4. Polar Effects

Sunspots can eject material from the sun that travels a few 100 km/s to a few 1,000 km/s. If the material is ejected with an Earth-bound trajectory, it will typically take a few days to reach Earth. Due to the Earth’s magnetic field, it tends to travel at the poles, where it can significantly impact the ionosphere at either pole. In addition to impacting GNSS performance, this can sometimes be observed as the Northern (or Southern) lights, a phenomenon referred to as aurora borealis (or aurora australis).

While a loss of lock and cycle slips can occur in the polar region, data typically shows less severe amplitude scintillation compared to the equatorial regions, with limited cycle slips and less disruption.


5. Global Effects

Although most noticeable disturbances occur around the equator and northern latitudes, Trimble has also observed an increase in the ionospheric delay measurement globally as we approach the solar cycle maximum. While dual- and triple-frequency techniques are leveraged to mitigate these effects by using an ionospheric-free combination, this also increases measurement and position noise. With the potential for large solar storms to cause disruptions in mid-latitude operations, ionospheric protection has become a critical global requirement for GNSS receivers.

How Trimble IonoGuard used in the field to mitigate ionospheric interference

Trimble’s IonoGuard technology offers a cutting-edge solution to the challenge of ionospheric interference, a common issue that can degrade the accuracy of GNSS signals. This technology utilizes advanced algorithms to mitigate the effects of all types of ionospheric disturbances on satellite signals, ensuring higher reliability and precision in GNSS positioning.

Through the use of Trimble GNSS receivers with Trimble ProPoint — which features Ionoguard technology — survey tasks can be completed even when there are unfavorable conditions present. With this innovation, Trimble strives to provide robust, accurate positioning solutions to meet the demands of modern GNSS users in 2025 and beyond.

Download the Trimble IonoGuard technical publication