What is carrier-phase ambiguity, and why is its resolution important?

• A. The exact phase of the carrier signal measured in degrees; not important.
• B. The unknown integer number of carrier cycles in phase measurements; resolving it yields centimeter- or millimeter-level accuracy.
• C. The amplitude of the carrier wave; resolving it improves signal-to-noise.
• D. The Doppler shift; resolving it improves velocity estimates.

Answer: (B)

Carrier-phase measurements track the phase of the carrier signal, but you only observe that phase modulo a full cycle. The unknown integer number of complete carrier cycles that have occurred between transmitter and receiver is the carrier-phase ambiguity. Resolving this integer count is crucial because once those ambiguities are fixed, the highly precise carrier-phase measurement translates into an accurate range between satellite and receiver, yielding centimeter- or millimeter-level positioning accuracy. In high-precision GNSS techniques, this ambiguity resolution is what unlocks the much finer accuracy that carrier-phase data can provide, compared to code-based range measurements. The other ideas—measuring the exact phase in degrees, focusing on amplitude, or using Doppler shift—do not describe the fundamental issue, which is the hidden integer number of cycles that must be determined to convert phase to a true distance.