Sichtbarkeitssensoren verstehen: Prinzipien, Anwendungen und Funktionen

In meteorology, transportation, and environmental monitoring, accurately assessing visibility is critical. Whether it’s fog drifting across an airport runway or smog creeping over a highway, poor visibility can pose serious safety risks. This is where visibility sensors come in—a compact but vital technology that provides continuous, real-time measurements of how far we can see through the atmosphere.

What Is a Visibility Sensor?

A visibility sensor is a meteorological instrument that measures atmospheric visibility, specifically the Meteorological Optical Range (MOR)—the distance at which a large, dark object can just be seen against the horizon sky. These devices are essential in applications ranging from weather stations and road safety systems to ship navigation and wind farms.

Modern visibility sensors are based on the forward-scattering principle, a significant evolution from traditional transmissometers. They are more compact, require less power, and are easier to install, making them well-suited for both fixed stations and mobile platforms, including drones.

How Do Visibility Sensors Work?

The core working principle of a visibility sensor relies on infrared light scattering. The system typically consists of:

• A light transmitter that emits pulsed infrared light,
• A receiver that detects the forward-scattered light caused by particles in the air (such as fog, dust, smoke, or rain),
• And a microprocessor that interprets the received signal.

As the light beam travels through the atmosphere, airborne particles scatter some of the light toward the receiver. The amount of scattered light is directly related to particle concentration. More particles mean more scattering, which results in lower visibility. The system then converts this data into MOR values using algorithms based on well-established models like the Koschmieder equation:

MOR (km) = 2.996 / σ,
where σ is the atmospheric extinction coefficient.

This method allows for reliable visibility measurements over a range typically from 5 meters to 80 kilometers.

Forward Scatter vs. Transmissometer

It’s worth noting that forward-scattering sensors do not measure the total extinction of light but instead focus on the scattering coefficient at a fixed angle (usually 42°). While transmissometers measure total extinction across a known distance, forward-scatter sensors infer visibility from light scattered at this fixed angle.

Although this difference exists, in practical use—especially when visibility is below 100 km—the results are closely correlated. This is because particle scattering (rather than absorption) dominates visibility degradation in typical atmospheric conditions.

Advanced Design Features

High-performance visibility sensors include several engineering optimizations:

1. Downward-facing optical lens with a protective shield to prevent contamination by rain or dust.
2. Electromagnetic and overvoltage protection, ensuring safe, reliable operation even in harsh environments.
3. High-speed sampling for better accuracy during rapidly changing weather, such as mixed rain and fog.
4. Corrosion-resistant housing made of alloy materials, suitable for long-term outdoor use—even in coastal or industrial environments.
5. Low power consumption—as low as 0.5W to 0.9W—ideal for solar-powered stations or UAVs.
6. Dual-output modes: RS485 and Wi-Fi for flexible integration into existing systems or cloud platforms.

Drones and Compact Visibility Sensors

The increasing use of drones for weather monitoring has driven demand for ultra-light, compact sensors. For instance, some mini visibility meters weigh under 60 grams and consume less than 1 watt of power, making them perfect for UAVs operating at high altitudes or in remote environments. These sensors often feature:

• Ultra-low wind resistance
• High resistance to electromagnetic interference
• Wide operating temperature range (as low as -20°C and up to 4000 meters elevation)

Applications Across Industries

Visibility sensors are indispensable across a wide range of sectors:

• Airports and Aviation: Runway visibility is critical for takeoffs and landings.
• Highways and Tunnels: Visibility data feeds into variable speed limits and warning systems.
• Maritime and Ports: Ensures safe docking and navigation.
• Weather Stations: Core component of automated meteorological stations.
• Wind Farms: Monitoring dust and fog for turbine maintenance planning.
• Industrial Sites: Detect visibility issues caused by emissions or particulates.

Conclusion

Visibility sensors may be compact, but their role is anything but small. By combining precise optics, robust design, and intelligent signal processing, these instruments deliver vital visibility data in real time—whether they’re mounted on a highway pole or flying high on a drone. As the demand for environmental awareness and automation grows, the importance of reliable visibility monitoring will only continue to rise.