The challenge of ionospheric scintillation in precision agriculture

By Haley Wiese, Agriculture Segment Manager, Hexagon’s Autonomy & Positioning division

Working in agriculture also means facing a variety of challenges imposed by nature. Unfavourable weather conditions, such as irregular rainfall, strong winds and hail, are common obstacles for producers and companies involved in the sector. Recently, however, a rise in solar flares has caused headaches for those who rely on precision agriculture, such as satellite positioning technologies, to operate farm machinery.

Ionospheric scintillation is a phenomenon that causes rapid and irregular variations in the intensity of radio frequency signals that travel through the ionosphere, a region of the Earth’s atmosphere that has ionised particles, which makes it capable of reflecting and refracting radio signals, such as those used in satellite communications and GNSS navigation systems.

These variations in the intensity of radio signals occur due to disturbances in the concentrations of free electrons in the ionosphere, which can be influenced by various factors, including solar activity, geomagnetic events and weather conditions in the upper atmosphere. Fluctuations in the electron density of the ionosphere cause distortions in radio signals, leading to fluctuations in the signal intensity, phase and frequency. Some of the consequences of this phenomenon are almost imperceptible, such as a small deviation of 1 or 2 meters in your cell phone’s GPS. When it comes to precision farming, however, a few centimetres of error in machine positioning can severely impact operations by increasing input waste, reducing efficiency and decreasing production.

Many farmers, especially in Brazil, plant and harvest two crops a year, and rely on precision farming technology to sow and harvest quickly and accurately. With an estimated production of 317.5 million tons for the 2023/24 harvest, according to the Brazilian National Supply Company (Conab), these producers have buffer time to keep their machines idle. During planting and harvesting periods, farms often operate 24 hours a day, 7 days a week, and precise positioning via GNSS is essential for the use of solutions such as auto steering and traffic control, for example. When ionospheric scintillation affects the performance of location systems, it causes delays and inaccuracies, directly impacting the productivity of farms and damaging the operations’ efficiency and profitability.

To mitigate the impacts caused by ionospheric scintillation, as well as other problems that can affect receivers, farmers have several GNSS correction options at their disposal, such as PPP (Precise Point Positioning), and RTK (Real-Time Kinematic). These alternatives aim to increase positioning accuracy for high-precision applications and create different levels of resilience against ionospheric interference. However, it can still affect these services, causing errors in the receiver’s position calculations. In RTK systems, which rely on carrier phase measurements, scintillation can drastically impair positioning accuracy, especially at greater distances from the base station.

To overcome scintillation challenges, PPP positioning is a more reliable option. Unlike RTK, PPP estimates ionospheric errors at the receiver’s location and does not depend on corrections from a local base station. This allows users to achieve high precision anywhere within the global coverage area, regardless of the distance from the base station. In addition, PPP takes into account the immediate ionospheric environment, making it less sensitive to changes in atmospheric activity.

A study by Hexagon | NovAtel in 2020, analysed the ionospheric activity in the central-western region of Brazil, comparing a standard RTK positioning solution and the PPP TerraStar-C PRO positioning solution, developed by NovAtel. A 24-hour data collection captured the nocturnal impacts of ionospheric activity and yielded some insights: while RTK position performance at 10 km from the base station was degraded for many hours, showing errors of up to 25 centimetres, the receiver using TerraStar-C PRO corrections continues to experience centimetre-level accuracy, with shorter maximum deviations of up to 10 centimetres.

In summary, ionospheric scintillation is a growing challenge for precision agriculture, affecting the productivity and efficiency of agricultural operations. To minimise its impacts, the adoption of correction services such as TerraStar-C PRO has proven to be a resilient and reliable solution, allowing farmers to continue their operations accurately and effectively, even in challenging conditions. The development of increasingly advanced precision solutions is crucial to ensuring the success of agriculture.