In carrier-phase GNSS observations, what is a cycle slip?

• A. A change in satellite constellation.
• B. A temporary loss of satellite lock.
• C. A disruption of phase tracking causing a jump in the tracked phase, breaking the phase continuity.
• D. A minor delay due to atmospheric refractions.

Answer: (C)

In carrier-phase GNSS, the phase of the received carrier is tracked very precisely to keep a continuous record of the measured phase. A cycle slip is a disruption of that phase tracking that causes an abrupt jump in the tracked phase, breaking the phase continuity. After reacquisition, the phase history may jump by an integer number of cycles, which disrupts the integer ambiguity and requires re-estimating the phase cycle count.

This is not about changing which satellites are visible, and it isn’t simply a temporary loss of lock itself or a smooth delay from the atmosphere. Those either describe different events or gradual effects, whereas a cycle slip refers specifically to the sudden phase jump that breaks continuity.