In our modern era, it is an often overlooked, but impressive nonetheless, fact that we can measure distances and locations to within millimetres of true accuracy. If you consider the sheer amount of satellite systems, ground facilities, surveyors and equipment in use to make this possible, it is a true harmony of interconnected systems.
However, in spite of this, RTK GPS can still have issues with accuracy. Although they may be less significant or regular than older options, like dumpy levels or DGPS systems, it is possible that occasional dips in accuracy may be expected. So what is responsible for these inconsistencies and what can surveyors do to reduce the likelihood of them? Get to know what affects GPS accuracy and what causes fluctuations in RTK performance to maintain its reliability better.
Ionospheric Delay
The ionosphere is one of the upper layers of Earth’s atmosphere, and it acts as a semi-physical barrier to the radio communication we use for interacting with our satellites. Understanding the nature of this delay is a relatively recent innovation, which is why you don’t typically see it included in DGPS devices.
Satellite Clock Errors
RTK GPS also improves on the formula and accuracy of surveying equipment operations by accounting for satellite clock errors. We are all likely familiar with the expression “time is relative,” but it doesn’t really affect our daily lives. With satellite clocks, however, it is a critical consideration and one that humanity has yet to perfect.
Rover Distance
A surprisingly “dumb” problem with accuracy comes from the rover and base stations’ relative distance to one another. Range boosters are often employed for difficult or treacherous surveys to counteract the loss in accuracy that comes with increasing distance.
Signal Interference
Although the technology and science behind these complex systems can make it seem like they work by some sort of magic, they are, in fact, working within some distinctly physical parameters. Therefore, one of the most common reasons for inconsistent data is signal interference from large objects. If the rover is in a valley without a GNSS receiver close at hand, there may be interference. This issue persists if doing work in modern settings as well.
Multipath Error
Multipath errors occur when GPS signals reflect off surfaces like buildings, bodies of water, vehicles, or rocky terrain before reaching the receiver. These reflections cause the signal to travel a longer path, which can distort the calculated position and lead to inaccurate measurements. In dense urban areas or rugged survey environments, this issue can create persistent inconsistencies if it’s not mitigated with proper antenna or signal processing.
A cold start happens when a GPS receiver powers on without any stored data about satellite positions, time, or previous coordinates. It must search for all available satellites from scratch, so it can take several minutes to achieve a usable fix, during which accuracy may be poor. This delay can slow down field operations and make positional drift more likely to appear until full lock is established.
A warm start occurs when the device retains partial satellite data, such as recent almanac or ephemeris information, but still needs to reacquire a stable connection. Although it’s faster than a cold start, it can still produce temporary fluctuations in accuracy as the receiver updates time and position corrections. Surveyors may notice inconsistent data during these first moments, especially in challenging environments.
GPS drift refers to gradual shifts in reported position over time, even if the device remains stationary. It is usually the result of satellite geometry, atmospheric changes, clock offsets, or minor calculation discrepancies that accumulate during extended use. Over longer surveys or mapping tasks, this drift can be what affects GPS accuracy unless corrected with RTK signals, base station references, or recalibration.
To get the most precise readings from an RTK or GNSS receiver, the device needs to be configured and used in conditions that support centimetre- or millimetre-level accuracy. Here are the most effective steps:
Reduce local interference and obstructions. Move away from power lines, reflective metal surfaces, vehicles, and dense structures that can distort or block incoming satellite signals.
Avoid trees, buildings, bridges, and machinery that can block or deflect satellite signals. Open sky access improves lock and reduces error sources.
Use an external antenna or pole mount when applicable. It reduces multipath issues and strengthens the signal-to-noise ratio.
Keep firmware and correction services current. Outdated firmware or expired NTRIP/network correction settings can limit accuracy.
Although there may be problems with achieving the highest level of accuracy, millimetre level corrections are often of little consequence. If you are looking to improve your accuracy or replace an inaccurate piece of equipment, contact us today. We offer helpful advice and product information!
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 403-286-0333 or email us [email protected]
