Which instrument is primarily utilized for navigation in low visibility conditions?

The correct choice is centered around the capability of GPS and similar navigational systems to function in low visibility conditions effectively. In aviation, when visibility is severely restricted due to weather conditions such as fog, rain, or snow, traditional navigational instruments might not provide sufficient guidance. GPS utilizes satellite signals to determine an aircraft's position and can operate independently of weather conditions, making it a reliable solution for navigation in such challenging environments.

While other instruments like VOR or ADF can be used for navigation, they may depend more on line-of-sight signals or specific ground stations, which can be problematic in low visibility. Additionally, radar altimeters serve a different purpose, primarily providing altitude information relative to the terrain directly beneath the aircraft, rather than assisting with navigational tasks. Thus, GPS stands out as the most suitable tool for navigation in scenarios where visibility is a critical issue.