Ground Visibility

Ground visibility is the prevailing horizontal visibility near the earth’s surface, as reported by a certified weather observer at an aerodrome. In METARs, visibility is reported in statute miles (SM) or metres. Ground visibility is what drives instrument approach minima — it is the official meteorological basis for determining whether an approach can be commenced or continued.

Ground vs. Flight Visibility

Ground visibility is measured at the surface. Flight visibility is what the pilot can see from the cockpit. The two can differ — for example, smoke aloft may restrict flight visibility while ground visibility is good. The pilot is responsible for maintaining the visibility required for the operation, regardless of what is reported on the ground.

Runway Visual Range (RVR)

In low-visibility conditions, visibility is often reported as Runway Visual Range (RVR) rather than in SM. RVR is measured by a transmissometer at the runway and reports visibility in feet or metres at the runway level. RVR is more precise and operationally relevant for approach minimums than a general aerodrome visibility report.

Related Terms

See also: RVR, Flight Visibility, Prevailing Visibility.