What does Dilution of Precision (DOP) quantify in GNSS positioning?

• A. The velocity of satellites
• B. A geometric factor that quantifies how satellite geometry degrades position/velocity/time accuracy
• C. The precision of gravity model
• D. The time dilation due to clock drift

Answer: (B)

DOP measures how the arrangement of satellites in the sky affects how measurement errors translate into position, velocity, and time errors in a GNSS solution. When you solve for your receiver’s position using measurements to multiple satellites, each reading has noise. The way that noise impacts the final estimate depends on where the satellites appear: if they are well spread across the sky, the equations constrain all directions well, so a small measurement error leads to only small position or time errors. If the satellites are clustered in a tight arc, the geometry provides weaker constraints and the same measurement noise can produce much larger errors.

DOP is purely a geometric factor derived from the satellite–receiver geometry; it does not represent satellite speed, gravity model accuracy, or clock drift. It’s used to describe how the geometry amplifies or attenuates the effect of measurement noise on the solution, with lower values indicating better geometry and higher potential accuracy.