GNSS in agriculture: Identifying the appropriate level of accuracy for each operation

January 28, 2025

It is common to hear the term GPS (Global Positioning System) used to refer to positioning and navigation tools in agriculture. However, what many do not know is that GPS is the name of the United States of America satellite positioning system. Most technologies applied in agricultural operations use GNSS (Global Navigation Satellite Systems), which describes the collection of satellite positioning systems from multiple countries including GPS (United States), GLONASS (Russia), Galileo (European Union), Beidou (China), NavIC (India) and QZSS (Japan). Regardless of the term used, if you are a farmer today, you probably use positioning technologies in your agricultural operations.

For several decades, positioning technologies have been essential for maintaining guidance lines and reducing gaps and overlaps, allowing users to operate more efficiently, especially in areas with uneven terrain. The list of benefits is long and includes optimisation and savings in Simply put, GNSS is the foundation of precision agriculture. However, the long journey that the signals take from the satellite to the receiver presents some challenges. along the signals path can cause delays, distortions and inaccurate positioning. To achieve and maintain accuracy, signal corrections are used.

Understanding how corrections work and identifying the ideal level of precision for each type of operation can help you make more effective decisions. Every farm is different, and every farmer operates differently. Therefore, outlined below are different types of correction services available that offer varying degrees of accuracy and delivery methods.

Traditional RTK technology compares data between a fixed-base station and receivers in the field to correct errors, assuming they both identify the same nearby errors. These corrections ensure high accuracy (1-2 cm), but the user must remain close to the base stations (10-30 km). The convergence time, approximately one minute, indicates the time to calculate the RTK position after receiving corrections data. Delivery can be via radio or mobile phone, requiring a fixed-base station or a 3G or 4G modem in the equipment.

For equipment with mobile internet modems, the technology is NRTK. These devices process satellite signals and send RTK corrections back to GNSS devices. The advantage is that the internet signal has the capacity to process a greater volume of data, ensuring reliable coverage, increasing productivity and, by solving availability and communication problems, seamlessly integrating positioning data into the farmer’s workflow.

Due to the high initial investment and the necessary proximity to the base station, this option is recommended for large commercial operations with static limits in areas with poor satellite visibility and a high number and variety of machine type

Precise Point Positioning (PPP)

The PPP method uses a network of reference stations to correct satellite errors, which can happen routinely but have been exacerbated this year by ionospheric scintillation. This is a natural phenomenon caused by solar flares, which involves rapid and irregular variations in the intensity of radio frequency signals through the ionosphere, a region of the Earth’s atmosphere that contains ionised particles. It causes distortions in radio signals, such as those used in satellite communications and GNSS (Global Navigation Satellite System) navigation systems.

With PPP, data is transmitted to the receiver in the field, improving real-time positioning accuracy. PPP is available globally, without being limited to the range of a base station. Pass-to-pass accuracy ranges from 2.5 cm to 15 cm, depending on the type of correction, and convergence times can range from less than 1 minute to about 18 minutes, depending on the type of signal. Corrections can be delivered via satellite or mobile, and only require a dual-frequency GNSS receiver and a subscription to the correction service, removing the need for local infrastructure like a fixed base station

RTK Bridging

RTK bridging is designed for RTK and PPP-RTK hybrid users. RTK acts as the main source of correct Rather than operating without RTK corrections and experiencing reduced accuracy, the receiver can use PPP corrections to maintain centimetre level accuracy until RTK corrections are re-established. This method, called bridging, guarantees continuity of operation with high precision, so you can keep operating instead of waiting for RTK corrections to return. Bridging services can range from 20 minutes to an unlimited outage coverage period, depending on the subscription level purchased. RTK bridging services are satellite delivered and require, at a minimum, a dual-frequency GNSS receiver and a RTK bridging subscription in addition to the existing RTK infrastructure.

Satellite-Based Augmentation Systems (SBAS)

Satellite-Based Augmentation Systems (SBAS) are free correction services managed by government organisations. They compare information from ground stations with data from satellites and send adjustments to other satellites, which transmit these corrections to receivers in farm equipment. Coverage depends on the region, such as WAAS for North America or EGNOS for Europe. They offer an accuracy of around 60 cm and have limited availability in some regions. The convergence time is approximately 5 minutes, and the corrections are delivered via satellite. Requirements include a single-frequency GNSS/GPS receiver in an SBAS-compatible region. This is an option for producers who want to start working with precision agriculture, but do not have the resources to invest in more precise technologies.

In this diverse universe of satellite corrections, where options vary between high and low precision and coverage, the integration of technology plays a central role in farming operations. Having receivers that support multiple frequencies and constellations is the first step to improving machine positioning. SMART Antennas, developed by Hexagon | NovAtel offer multi-constellation and multi-frequency tracking and features flexibility and upgradeable software. Combined with TerraStar Correction Services, the solutions offer a wide range of options to adapt to the needs of each operation. Fortunately, no matter what type of crop or cultivation method you adopt, there is an accuracy level to meet your needs.