Why Your RTK Drone Suddenly Drops to FLOAT
Space weather explained for drone pilots, surveyors, and GNSS professionals
Overview
RTK drones rely on extremely precise satellite signal tracking to maintain a FIX solution. When conditions are ideal, centimeter-level accuracy is possible. But during periods of space weather activity, RTK systems can suddenly lose FIX and fall back to FLOAT.
While common causes include obstructions, multipath, and radio link issues, this transition can also be caused by disturbances in the ionosphere affecting GNSS signals — especially during geomagnetic storms.
What “FIX” Actually Means
A FIX solution means the receiver has resolved the integer ambiguities in the carrier-phase measurements from satellites. This allows precise positioning.
To maintain FIX, the receiver must continuously track the phase of signals from multiple satellites without interruption.
The Ionosphere’s Role
GNSS signals pass through the ionosphere, a region filled with charged particles. During solar activity, this layer becomes unstable.
The disturbances cause:
- Rapid changes in signal delay
- Signal fading (scintillation)
- Phase shifts that confuse the receiver
Why RTK Is So Sensitive
RTK relies on measuring the phase of signals, not just the code. Phase tracking requires very stable conditions.
When ionospheric irregularities cause rapid phase changes, the receiver can no longer maintain integer ambiguity resolution. This forces a drop from FIX → FLOAT.
What Happens During a Drop to FLOAT
When FIX is lost:
- Position accuracy degrades from centimeters to decimeters or worse
- Survey-grade consistency is lost
- Mapping datasets may contain distortions
- RTK reinitialization is required
Why It Happens Even with a Nearby Base
Many operators assume short baseline distance prevents problems. However, ionospheric disturbances can vary rapidly even over short distances, and RTK correction models assume smooth ionospheric behavior.
During geomagnetic storms, this assumption fails.
Solar Activity Triggers
RTK drops are more likely during:
| Event | Effect |
|---|---|
| Solar Flares | Sudden ionization increase |
| Geomagnetic Storms | Large-scale ionospheric instability |
| High Kp Index | Increased positioning risk |
Practical Impact for Drone Pilots
When RTK drops to FLOAT during a mission:
- Flight control generally remains stable, though some autopilot platforms may experience position jumps during RTK transitions
- Position tagging accuracy decreases
- Post-processing corrections increase
- GCPs may be required
Monitoring space weather helps anticipate these events.
Key Takeaways
- FIX loss can be atmospheric — during geomagnetic storms it becomes the dominant cause, but obstructions, multipath, and radio link issues are equally common in routine operations
- RTK is extremely sensitive to ionospheric instability
- Solar storms increase the likelihood of FLOAT conditions
- Monitoring GNSS space weather reduces mission risk