RTK Multipath Sensor Fusion: Maritime Challenges & Solutions
Estimated reading time: 6 minutes
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Summary
Maritime multipath (reflections from water, metal, docks, bridges) can make RTK positions jump or lag—especially during docking and tight turns. Combining multi-frequency GNSS with tightly-coupled INS, robust filtering, and good antenna practice keeps vessels on course with cm-level accuracy when conditions allow.
Key takeaways
- RTK + sensor fusion holds cm-level positioning in ports and channels when correction age stays low and sky view is managed.
- Multipath from water and structures is the main marine challenge; it can cause jumps, lags, and re-initialisations.
- Mitigation stacks: multi-constellation/multi-frequency, Kalman & wavelet filters, MEDLL, carrier-smoothing, and vendor features (e.g., APME+, ProPoint).
- 3D scene models, camera-based NLOS checks, and AI can reject reflections in real time.
- Tightly-coupled GNSS/INS bridges dropouts and smooths multipath, provided the system is calibrated and logs are monitored.
Overview of Real-Time Kinematic (RTK) Positioning
RTK uses base/network corrections with carrier-phase measurements to reach cm-level accuracy. In busy ports and narrow channels, RTK multipath sensor fusion blends GNSS with IMU/INS so the vessel maintains a stable solution even when satellites are blocked or reflections rise.
Challenges of Multipath Propagation in Marine Settings
Reflections from water, metal decks, docks, bridges, or cranes arrive late and bias measurements. Superstructures shadow satellites; storms and tall shores cut visibility. Radios and other gear add RF noise. The result: more cycle slips, longer convergence, and unstable Fix—exactly when precision matters most.
Solutions to Mitigate Multipath Interference
Receivers & signals. Use multi-frequency, multi-constellation GNSS (GPS, Galileo, GLONASS, BeiDou) for redundancy and faster ambiguity resolution.
Algorithms. Apply adaptive filters (e.g., Kalman, wavelet), MEDLL, and carrier-smoothing; enable vendor multipath features such as APME+ or ProPoint where available.
Situational awareness. Employ 3D scene models and camera-based NLOS detection; AI can flag/refuse likely reflections in real time.
Hardware & install. Mount antennas high and clear, away from masts/reflectors; use quality radomes, low-loss marine coax, and consider choke-ring or ground-plane solutions.
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Impact of Sensor Fusion on Navigation Accuracy
Tight coupling lets GNSS provide absolute truth while the INS bridges short gaps, smooths multipath jumps, and stabilises heading. Best practices: keep IMU/GNSS calibration current, verify correction streams and mountpoints, and apply post-mission filtering to clean logs.
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Frequently asked questions
What is RTK multipath sensor fusion?
It combines RTK (cm-level GNSS with corrections) and sensors like IMUs/INS so the vessel maintains stable positioning when GNSS is blocked or affected by reflections.
Why is maritime multipath so problematic?
Water and metal create strong reflections; signals arrive late and bias the solution, causing jumps or lag—especially during docking and tight turns.
How can multipath interference be mitigated?
Use multi-frequency, multi-constellation GNSS, adaptive filtering (Kalman, wavelet), MEDLL, carrier-smoothing, and vendor features (e.g., APME+, ProPoint). Add 3D/NLOS checks and AI filtering where possible.
How does INS help during outages?
With tight coupling, INS bridges short gaps, smooths multipath jumps, and stabilises heading while GNSS re-locks ambiguities.
Which antenna setups reduce marine multipath?
Mount high and clear, away from masts/reflectors; use quality radomes, ground planes or choke-rings, low-loss marine coax, and keep cables/connectors in good condition.