With more and more of our customers picking up RTK for the first time, there are a lot of questions around what effects RTK performance, and why their receiver performs better in one location but worse in a different. Despite this, whether you’re staking out a boundary, performing topographic surveys, or mapping infrastructure, RTK is the go-to technology for high-precision positioning. However, the performance of RTK systems can be influenced by several factors, some environmental and some technical.
As a surveyor, it’s essential to understand these factors so you can maximize the performance of your RTK equipment and troubleshoot issues when they arise. In this post, we’ll explore the key elements that affect RTK accuracy, including multipath interference, ionospheric effects, message type, satellite technology, and solar activity. Understanding how each of these factors influence your GNSS performance will help you avoid common misunderstandings and ensure your surveys are accurate, consistent, and reliable.
Multipath Interference: The Modern Surveyor’s Challenge
Ionospheric and Tropospheric Effects: Atmospheric Influences on Accuracy
RTK Message Types: Data Transmission and Accuracy
Satellite Technology and GNSS Constellations: The Backbone of RTK Performance
Conclusion: Maximizing RTK Performance in the Field
One of the most common questions I get about RTK equipment from surveyors is around multipath. I hear from people all the time asking why receivers will fix in one location, but will struggle in another. By understanding what is actually happening to the signals before they arrive at the receiver can help explain what is happening on their receiver.
Multipath interference refers to the phenomenon where GNSS signals bounce off nearby objects—such as buildings, trees, water bodies, or even the ground—before reaching your receiver. This additional reflection path results in delayed and distorted signals, which can significantly degrade positional accuracy. For surveyors working in environments where obstacles are unavoidable, multipath interference is a major concern.
Urban Environments and Multipath
Urban environments present the most challenging conditions for RTK due to the abundance of reflective surfaces. Tall buildings and metal structures act as mirrors for GNSS signals, causing reflections that confuse the receiver. This can lead to “urban canyon” effects, where the rover experiences positional shifts, erratic movements, or slow convergence times. In extreme cases, you may lose the RTK fix entirely.
A couple of years ago, a couple of us went into downtown and put receivers up against a large sky scraper with an entire face coated in glass. As the RTK receiver picked up both the direct and reflected signals, the result is a longer calculated distance from the satellite to your receiver. This error, known as “signal delay”, can cause your positioning to shift by several centimeters—or even meters—off the true location. For more information on multipath, check out this article: Surveying with RTK – What Does Multipath Mean?
Mitigation Techniques for Multipath
Fortunately, there are several strategies for reducing the impact of multipath interference:
The ionosphere and troposphere are two layers of the Earth’s atmosphere that can alter the speed and accuracy of GNSS signals. Both layers introduce delays, distortions, and refraction that impact the time it takes for signals to travel from the satellite to your RTK receiver.
Ionospheric Delay
The ionosphere, is located between 30 and 600 miles above the Earth’s surface and consists of multiple different layers. Although a lot of really interesting chemistry occurs throughout this region (at least to me, a guy with a background in chemistry), the important thing for surveyors to understand is that this layer contains a large number of charged particles. As solar radiation strikes the atmosphere, gas particles are quite literally blown apart, creating charged ions (hence the ionosphere). These charged particles can in turn affect electro-magnetic signals as they pass by.
One of the major causes of ionospheric delay is solar activity. During periods of heightened solar activity, such as solar flares or geomagnetic storms, the ionosphere becomes highly charged, leading to increased signal disruption. These effects are most pronounced during the day and in equatorial regions but can affect RTK operations worldwide. Fun fact, this solar activity is the source of Northern Lights in the nights sky.
Mitigation of Ionospheric Delay
To combat ionospheric delay, RTK systems employ several techniques:
Tropospheric Delay
The troposphere, located below the ionosphere, consists of the air and water vapor surrounding the Earth’s surface. It is the portion we live in, and that supports the vast majority of life on Earth. As GNSS signals pass through this layer, they are affected by changes in temperature, pressure, and humidity. Water vapor, in particular, can slow down the signals, leading to tropospheric delay. You can think about it in a manner similar to a straw in a glass of water. As you transition from air to water in your cup, the density changes, refracting the light waves. This is what is happening to your receiver.
This delay is especially significant in areas with high humidity or over long distances, such as in coastal or mountainous regions. Unlike ionospheric delays, which can be mitigated with dual-frequency receivers, tropospheric delays are more challenging to correct, especially in highly variable weather conditions.
Mitigation of Tropospheric Delay
RTK systems often include tropospheric models that predict the amount of delay based on environmental factors like temperature and humidity. These models use elevation data and weather information to make real-time corrections, improving accuracy in difficult atmospheric conditions. These models need to correct for a “dry” and “wet” component (as usual water is making everyone’s life more complicated, a chemist’s nightmare).
For surveyors, understanding the local weather patterns can help you predict when tropospheric delays are likely to impact your RTK performance. For instance, if you are expecting a very intense storm, or a repaid and dramatic change in temperature in a very short amount of time, you may experience a bit more variability in your results.
A lesser-known but equally important factor affecting RTK performance is the type of correction messages your system is receiving. RTK corrections are sent from a base station to the rover, and the efficiency, accuracy, and reliability of these transmissions play a critical role in your overall performance.
Open Source and Proprietary
There are two primary message formats used for transmitting RTK correction data:
Both these types of messages are reliable, but the choice between them depends on your equipment and the transmission medium. Some systems perform better with one format over the other due to the structure of the correction data and how it’s processed by the receiver.
Choosing the Right Message Type
As a surveyor, it’s important to ensure that your receiver is compatible with the correction format you’re using, whether it’s RTCM or another format. Ensure your equipment is set to receive the most recent versions of these messages to take advantage of improvements in data compression and transmission efficiency. Depending on the version of the message, it may also not transmit the latest signals.
For instance, Trimble’s CMR format only transmits GPS, GLONASS L1/L2, whereas CMRx (which is only available on Trimble receivers) transmits all available signals and constellations. In general, for most users, the best format to use is the RTCM 3 MSM or RTCM 3.2 message type.
RTK technology is fundamentally dependent on satellites, and the number, type, and quality of these satellites directly impact the accuracy and reliability of your RTK system. Over the past few decades, the field of satellite technology has expanded beyond the traditional GPS (Global Positioning System, built by the American’s) constellation to include additional systems such as GLONASS (built by the Russians), Galileo (built by the EU), and BeiDou (built by the chinese) and several other regional constellations. Together, these systems are referred to as GNSS (Global Navigation Satellite System) constellations.
Advantages of Multi-GNSS Receivers
Modern RTK receivers can access multiple GNSS constellations simultaneously. This provides several key advantages:
Advances in Satellite Signal Technology
In addition to accessing multiple GNSS constellations, modern satellites broadcast signals on newer frequencies designed to enhance precision. For example, the L5 frequency, used by newer GPS, Galileo, and BeiDou satellites offers improved signal stability and reduced susceptibility to interference, especially in multipath environments.
The L5 signal is designed specifically for high-precision applications like surveying, providing better performance in urban environments and areas with potential for interference. Over time, as more L5-capable satellites are launched and RTK receivers are updated to take advantage of these new signals, surveyors can expect continued improvements in accuracy and reliability.
Satellite Constellation Selection
When configuring your RTK equipment, it’s important to ensure that your receiver is set to track all available GNSS constellations. Some older RTK receivers may only track GPS and GLONASS, missing out on the benefits provided by Galileo and BeiDou.
In regions where Galileo and BeiDou satellites are more prevalent, these systems can provide valuable additional satellite coverage, reducing downtime and improving accuracy in difficult environments. Surveyors should check their receiver’s capabilities and enable all available constellations for optimal performance.
RTK technology has transformed the way surveyors work, offering real-time, centimeter-level accuracy that dramatically improves efficiency. However, to fully leverage the power of RTK, surveyors must understand the factors that can influence its performance.
Multipath interference, ionospheric and tropospheric effects, correction message types, and satellite technology all play critical roles in determining the accuracy and reliability of RTK positioning. By being aware of these factors and taking steps to mitigate their impact, you can ensure your RTK system delivers optimal performance in any environment.
Investing in high-quality equipment, keeping up with satellite technology advancements, and understanding how atmospheric conditions affect GNSS signals will help you consistently achieve the precision and reliability needed for today’s complex surveying projects. Whether you’re working in an urban jungle, a forest canopy, or along a coastline, mastering these variables will make a significant difference in the quality of your results.
In open areas, your RTK receiver has a clear line of sight to GNSS satellites, allowing it to receive undistorted signals. In urban environments, however, multipath interference becomes a significant issue. This occurs when GNSS signals bounce off reflective surfaces like buildings, causing delayed, distorted signals to reach your receiver. This can lead to position errors or slow convergence times. To mitigate this, surveyors can use multipath-resistant antennas, deploy the receiver in open areas when possible, or take advantage of advanced signal processing in high-end receivers.
Solar flares release high levels of radiation that interact with the Earth’s ionosphere, increasing the density of charged particles in the atmosphere. This can cause signal delays, loss of satellite lock, and degradation of positional accuracy in your RTK system. These effects are more pronounced during the day and in polar or equatorial regions. Using dual-frequency receivers and monitoring space weather forecasts can help mitigate the impact of solar flares on your RTK performance.
Both the ionosphere and troposphere are atmospheric layers that GNSS signals must pass through, and each can introduce delays and distortions:
Ionospheric delay is caused by charged particles in the ionosphere, especially during periods of high solar activity. These delays can be mitigated with dual-frequency receivers that can correct for ionospheric distortions.
Tropospheric delay occurs when signals slow down due to moisture, temperature, and air pressure changes in the troposphere. Tropospheric models, integrated into modern RTK systems, help predict and correct these errors, but they are harder to fully mitigate, especially in highly variable weather conditions.
RTK is widely used in surveying, construction, precision agriculture, and autonomous systems like drones and self-driving cars, where high positional accuracy is crucial for tasks like mapping, machine guidance, and resource optimization.
Modern RTK receivers now support multiple GNSS constellations, such as GPS, GLONASS, Galileo, and BeiDou, which enhances positional accuracy and reliability. Key benefits include:
Improved Satellite Visibility: With access to multiple constellations, you have better satellite coverage, reducing downtime and errors in challenging environments.
Reduced Convergence Time: More satellites mean faster calculation of fixed positions, allowing for quicker survey results.
Better Satellite Geometry: Multi-constellation systems improve the distribution of satellites in the sky, leading to more accurate position calculations. Additionally, newer satellites broadcast on advanced frequencies like L5, which offers improved performance, especially in multipath-prone environments.
Bench Mark Equipment & Supplies is your team to trust with all your surveying equipment. We have been providing high-quality surveying equipment to land surveyors, engineers, construction, airborne and resource professionals since 2002. This helps establish ourselves as the go-to team in Calgary, Canada, and the USA. Plus, we provide a wide selection of equipment, including global navigation satellite systems, RTK GPS equipment, GNSS receivers, and more. We strive to provide the highest level of customer care and service for everyone. To speak to one of our team today, call us at +1 (888) 286-3204 or email us at [email protected]
North America’s #1 supplier of land surveying equipment and instruments.
