Definition
Visibility sensors are the runway-mounted instruments used in a Runway Visual Range (RVR) system to measure how far a pilot can see down the runway. Modern RVR installations use forward-scatter visibility sensors, which shine a beam of light across a small sample of air and measure how much of that light is scattered by fog, mist, precipitation, or other obscurations. The scatter measurement is converted into a visibility value, which the RVR system then reports in feet for the runway.
Plain English
Small instruments placed near the runway that measure how clearly someone can see through the air. Their readings are used to tell pilots how far they can see down the runway.
Context Anchor
Seen in instrument procedure and airport weather discussions, especially when runway visual range is being reported for low-visibility takeoffs or landings.
Derivation
“Visibility” comes from words meaning “able to be seen.” “Sensor” comes from a root meaning “to feel or perceive.” Together, the term means equipment that detects how well things can be seen, rather than a person judging it by eye.
Why Pilots Care
Accurate readings from these sensors determine whether weather meets takeoff or landing minimums.
Intuition Check
Do not read “visibility sensors” as a pilot simply looking outside and estimating visibility. In this context, it means installed equipment that measures visibility conditions for official runway reports.
Example Sentence 1
The tower reported the RVR had dropped to 1,800 feet after the visibility sensors detected thickening fog near the touchdown zone.
Example Sentence 2
Controllers rely on visibility sensors to update RVR reports when conditions change rapidly.