What is Differential GNSS (DGNSS) and how do SBAS and RTK differ in terms of coverage and accuracy?

• A. DGNSS uses reference stations to correct signals; SBAS provides wide-area corrections with moderate accuracy; RTK uses nearby baselines to achieve centimeter-level accuracy with high locality.
• B. DGNSS is a precise method with centimeter-level accuracy everywhere; SBAS and RTK are less accurate.
• C. RTK provides wide-area corrections but not local coordinates.
• D. SBAS provides centimeter-level corrections everywhere.

Answer: (A)

Differential GNSS works by using measurements from fixed reference points to estimate the errors affecting GNSS signals and then sending those corrections to a rover. SBAS is a way to distribute those corrections over a wide area through geostationary satellites, so you get corrections across large regions, but with a level of accuracy that is good and reliable yet not as tight as local real-time fixes. RTK takes a different path: it relies on a nearby base station (or a network of bases) to compute carrier-phase corrections and transmit them to the rover, delivering centimeter‑level accuracy, but only over a local area defined by how far the corrections can effectively travel. So SBAS gives broad coverage with moderate accuracy, while RTK provides very high accuracy at short, local ranges.