Which type of navigation relies solely on instruments and does not require visual reference to the ground?

Instrument navigation is the correct choice because it involves navigating an aircraft using instruments rather than visual references from the ground. This method is crucial in situations where visibility is poor, such as during clouds, fog, or night-time operations.

In contrast, dead reckoning relies on calculating the current position based on a previously known location, using speed, time, and course, but still may involve visual references. GPS navigation, while a form of instrument navigation, often does incorporate visual ground references when displaying the aircraft's position on a map or screen. Visual navigation, by definition, requires the pilot to visually reference the ground or landmarks, which does not align with the requirement of not needing any such references. Thus, instrument navigation stands out as the method that relies solely on instruments for navigation.