Which observation type provides centimeter- to millimeter-level precision only after resolving integer ambiguities?

• A. Pseudorange observations provide centimeter- to millimeter-level precision with ambiguity resolution.
• B. Carrier-phase observations provide centimeter- to millimeter-level precision with ambiguity resolution.
• C. Pseudorange observations provide no precision advantage over carrier-phase.
• D. Carrier-phase observations require no ambiguity resolution to achieve high precision.

Answer: (B)

Carrier-phase observations provide centimeter- to millimeter-level precision only after resolving integer ambiguities. The phase of the carrier wave can be measured extremely precisely, but the measurement is inherently ambiguous by an unknown integer number of whole wavelengths between the satellite and the receiver. Determining that integer (the ambiguity) and fixing it lets you convert the measured phase into an accurate range, delivering cm–mm accuracy. Pseudorange is code-based and is inherently noisier, giving typically meter-level precision and not relying on fixing integer cycle counts. So the high-precision result that requires resolving those integers points to carrier-phase observations.