Differential GPS (DGPS) performance: which statement best represents typical position accuracies as a function of rover distance from the reference station?

Introduction / Context:
Differential GPS (DGPS) corrects many common-mode errors by referencing a fixed base station. Accuracy depends on baseline length (distance from rover to reference), ionospheric conditions, and whether code-based or carrier-phase techniques are used. This question targets typical code-based DGPS performance over short baselines.

Given Data / Assumptions:

• Standard real-time code-based DGPS corrections.
• Short baselines in the 1–2 km range with good geometry.
• No advanced RTK carrier-phase ambiguity resolution (which can reach centimetre level).

Concept / Approach:
As the rover moves farther from the reference, spatial decorrelation of errors (ionosphere, troposphere) reduces the effectiveness of differential corrections, degrading accuracy. Over very short baselines, DGPS commonly achieves around 1–2 m horizontal accuracy. Larger baselines (tens of kilometres) show several metres of error, unless more sophisticated techniques (e.g., RTK, network RTK) are used.

Step-by-Step Solution:
Identify the code-based DGPS accuracy regime (metre-level).Note best performance at short baselines ~1–2 km: ~1–2 m accuracy.Recognize accuracy degrades with longer baselines to several metres.Therefore, select the statement describing ~1–2 m at ~1–2 km.

Verification / Alternative check:
Manufacturer datasheets and field results commonly cite ~1–3 m DGPS accuracy under good conditions for short baselines, improving to sub-metre only with augmentation or carrier-phase techniques.

Why Other Options Are Wrong:

• 2–5 m at 2–5 km or 5–10 m at 5–10 km/25 km represent degraded performance relative to best-case short baselines.
• 0.1 m without carrier-phase is unrealistic for code-based DGPS.

Common Pitfalls:
Conflating DGPS with RTK; ignoring baseline dependence; assuming advertised best-case values apply at all distances.

Final Answer:
Positional accuracies ~ 1 – 2 m if rover is less than 1–2 km from the reference station