What happens to the Doppler navigation system when the flight is conducted over very smooth sea?

When a flight occurs over very smooth sea surfaces, the characteristics of the Doppler navigation system can change due to the unique radar returns from the water. In this scenario, the Doppler radar may detect minimal variation in the return signals caused by the uniform surface. As a result, the system may have fewer reference points for calculating speed and direction changes accurately.

This can lead to conditions where the system activates memory mode. In memory mode, the navigation system relies more on stored data rather than live input, which helps maintain navigation accuracy in situations where real-time inputs become less reliable. The transition to memory mode allows the system to continue providing navigational information despite the lack of effective Doppler tracking due to the smooth sea conditions.

Other options refer to either a complete inactivity or a reduction of effectiveness without acknowledging the specific navigation system's adaptations in response to environmental conditions, which does not correctly capture the complexities of how the Doppler navigation system functions in this context.