Sichtweiten

Sichtweiten describe the maximum distance at which a person with normal vision can perceive a prominent object of standard size and contrast against the background, under given atmospheric conditions. In meteorology, Sichtweite refers to horizontal visibility near the ground and is a key parameter for weather observations and forecasts. Sichtweiten are affected by atmospheric phenomena such as fog, mist, haze, rain or snow, dust and smoke, as well as by humidity, light conditions and background contrast.

Measurement methods range from manual estimation by trained observers to automatic instruments. Manual observations typically involve estimating the distance to a clearly defined landmark or marker. Automatic methods include transmissometers, which measure the attenuation of a light beam through the atmosphere, and forward-scatter or nephelometer instruments that assess the amount of scattered light to infer visibility. In aviation, additional precision is provided by runway visual range (RVR) sensors that quantify visibility along a landing course.

Use and significance vary by sector. Visibility values are routinely reported in weather forecasts and meteorological bulletins and inform weather warnings. They are crucial for road safety, affecting driving conditions and speed advisories, and for aviation and maritime operations, where low Sichtweiten can limit takeoff and landing or navigation options. While the general concept is shared, reporting conventions and thresholds can differ by country and by the specific operational context.