What is the purpose of ambiguity resolution in RTK?

• A. It resolves the integer number of carrier-phase cycles between satellite and receiver, enabling centimeter-level accuracy in real time.
• B. It fixes the receiver's height using a known datum.
• C. It determines the satellite ephemeris accurately.
• D. It calibrates the pseudorange measurements.

Answer: (A)

Ambiguity resolution in RTK is about determining the integer number of carrier-phase cycles between the satellite transponder and the receiver. The carrier-phase measurements are extremely precise, but they are only known up to an unknown integer number of full wavelengths. Without resolving that integer, the distance to each satellite is ambiguous by multiples of the carrier wavelength, so you can’t obtain a fixed, high-precision baseline.

By using double-differencing between a base station and the rover, many common errors cancel, leaving the remaining unknowns, including these integers, to be solved. Once the correct integer values are identified and fixed, the residual problem becomes a precise baseline measurement, delivering centimeter- to even millimeter-level accuracy in real time. This fixed solution is what lets RTK provide real-time precise positioning.

Other aspects like fixing the rover’s height to a known datum, accurately determining satellite ephemeris, or calibrating pseudorange measurements are important in GNSS processing, but they address different parts of the system and are not what ambiguity resolution accomplishes.