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What is Multipath Error and How It Degrades GPS Accuracy
DGPS
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02 Oct 2025Trishunya Team
Did you know? Multipath error near tall buildings or metal structures can sometimes shift a raw GPS reading by several metres, far beyond what any survey tolerance allows.
What is Multipath Error and How It Degrades GPS Accuracy
A GPS satellite signal travels roughly 20,000 kilometres to reach a receiver on the ground. On that final stretch, near the ground, the signal can bounce off buildings, water surfaces, vehicles, or even dense foliage before arriving at the antenna. This bounced, delayed arrival is called multipath error, and it is one of the most persistent accuracy problems in real-world GPS survey work, particularly in urban and industrial environments.
5m+
Possible error near reflective surfaces
90%
Multipath reduced with good antenna design
15°
Typical satellite mask angle to reduce error
Zero
Tolerance for multipath in precision stakeout
How Multipath Actually Corrupts a Position Fix
A GPS receiver calculates position by precisely timing how long each satellite signal took to arrive. A direct signal path gives an accurate timing. A reflected signal path is longer than the direct path, arriving slightly later, which the receiver may mistakenly interpret as extra distance to that satellite. This false distance measurement pulls the calculated position away from the true location.
Where Multipath is Most Severe
Surveying near tall structures like this requires extra care, since reflected signals here can silently corrupt an uncorrected position fix.
Urban Canyons
Tall buildings on either side of a street create repeated signal reflections, sometimes making GPS nearly unusable without correction.
Near Water Bodies
Calm water surfaces reflect signals almost like a mirror, causing significant multipath for coastal and reservoir survey work.
Industrial Sites
Large metal structures, tanks, and equipment reflect signals unpredictably, requiring careful antenna placement.
Dense Tree Canopy
Foliage causes both signal blocking and scattering, degrading both signal strength and position accuracy simultaneously.
How Survey-Grade Equipment Fights Back
1
Antenna Design
2
Elevation Masking
3
Signal Filtering
4
Extended Occupation
Multiple satellite signals converging on a receiver behave somewhat like this network, except reflections introduce noise into the connections.
Practical Field Strategies
Situation
Recommended Approach
Urban construction site survey
Use Total Station for critical points near buildings, DGPS for open areas
Reservoir shoreline survey
Position rover away from open water edges when possible during static observations
Industrial facility mapping
Increase occupation time near large metal structures for averaging benefit
Can multipath be completely eliminated?
Not entirely in challenging environments, but experienced survey crews recognize high-risk locations and either use alternative equipment like Total Station, or apply extended occupation and post-processing techniques to minimize its impact substantially.
Does multipath affect drone survey the same way?
Less severely, since drones fly at altitude with a clearer sky view than ground-level receivers, but multipath can still affect flights near tall structures or over water, which is why GCPs on the ground remain important for anchoring accuracy.
Why this matters for your project
If your site includes tall buildings, large water bodies, or heavy industrial structures, mentioning this to your survey provider upfront allows them to plan equipment and technique choices that avoid multipath-related accuracy problems before they happen.
Our field crews recognize multipath-prone environments and adjust method and equipment accordingly, ensuring reliable accuracy even in challenging urban or industrial settings. Learn more about our DGPS and RTK survey services.
