Introduction
What if we could measure GNSS errors at a known location and tell nearby receivers exactly how to fix them? That's the core idea behind Differential GNSS.
The Fundamental Insight
Errors are correlated over distance.
If a base station at a known location measures a 5-meter error from a satellite, a rover within 100 km will see almost the same error. The signal passes through nearly the same atmosphere, and satellite clock/orbit errors affect everyone equally.
How DGNSS Works
- Base station set up on a point with known coordinates
- Base station calculates position from satellites
- Difference between true and calculated position = total error
- Base station broadcasts corrections (PRC for each satellite)
- Rover receives and applies corrections
- Rover calculates improved position (decimeter accuracy)
DGNSS vs. RTK
| Feature | DGNSS | RTK |
|---|---|---|
| What's corrected | Code measurements | Carrier phase |
| Accuracy | 0.3–1 meter | 1–5 cm |
| Range | 100–200 km | 10–30 km |
| Complexity | Lower | Higher |
| Use case | Mapping, marine | Surveying, construction |
Accuracy vs. Distance
| Distance from Base | Typical Accuracy |
|---|---|
| <50 km | 0.3–0.5 m |
| 50–100 km | 0.5–0.8 m |
| 100–200 km | 0.8–1.5 m |
| >200 km | 1.5–3 m+ |
Real-World Applications
- Marine Navigation: Harbor entrances, narrow channels, 1–3 m accuracy
- Precision Agriculture: Variable rate application, soil sampling, 30–50 cm
- GIS Data Collection: Mapping utilities, resources, 50 cm – 1 m
CORS Networks
Continuously Operating Reference Stations:
- Permanent base stations covering entire regions/countries
- Users connect via internet (NTRIP)
- No need to set up your own base
Vital Points
- DGNSS uses a known base station to broadcast corrections
- Common errors are correlated over distance
- Accuracy: 0.3–1 meter depending on distance
- Range: up to 200 km from base
- CORS networks provide corrections without your own base