How is vertical visibility defined?

Vertical visibility is defined as the greatest distance that one can see vertically into a total obscuration, such as fog, haze, or precipitation. This measure is crucial for aviation and meteorological observations as it helps in assessing the conditions affecting aircraft visibility during takeoff, landing, or in-flight operations. When visibility is reduced, especially in vertical contexts, understanding how far one can see straight up into obscured conditions becomes essential for ensuring safety and appropriate decision-making.

In this context, the other options do not align with the definition of vertical visibility. The first choice refers to horizontal visibility at the horizon level, while the second choice is concerned with the visibility along a runway or toward lights, which also does not pertain to the vertical aspect. The last option indicates general visibility from an observation point without specifying the vertical dimension or total obscuration. Hence, the correct answer, which focuses specifically on how far visibility extends within obscured vertical conditions, accurately captures the essence of vertical visibility as defined in meteorological terms.