What is a visibility meter?

A visibility meter, also known as a visibility sensor or visibility instrument, is a device used to measure the distance at which objects or targets can be clearly discerned in the atmosphere. It provides a quantitative assessment of visibility, indicating how far an observer can see under prevailing atmospheric conditions. Visibility meters are essential tools in meteorology, aviation, transportation, and environmental monitoring.

Front View

These instruments come in various forms, but two common types of visibility meters are transmissometers and forward scatter sensors:

1. Transmissometers: Transmissometers operate by emitting a light beam from a source to a receiver, typically positioned at a known distance away. The sensor measures the amount of light that reaches the receiver, and by comparing the transmitted light with the received light, it can determine the visibility. This type of visibility meter is effective in assessing visibility in clear air, as well as in the presence of fog, mist, or other obstructions.

2. Forward Scatter Sensors: Forward scatter sensors measure the scattering of light caused by suspended particles in the atmosphere, such as fog, smoke, or haze. These sensors use a light source and a detector placed at a certain distance apart. The amount of scattered light reaching the detector is related to the visibility, allowing for the assessment of visibility in challenging atmospheric conditions.

The basic principle of a visibility meter involves emitting a light signal (usually infrared or visible light) and measuring the intensity of the light that returns after passing through the atmosphere. The attenuation of the light signal due to scattering and absorption by particles in the air provides an indication of visibility.

Here's how a typical visibility meter works:

1. Light Emission: The meter emits a beam of light, which can be a continuous wave or a series of pulsed light. The choice of wavelength depends on the specific application and the particles present in the atmosphere. For example, infrared light is often used because it is not affected by changes in sunlight or artificial lighting.

2. Attenuation Measurement: The emitted light beam travels through the atmosphere and its intensity is reduced by interactions with airborne particles such as dust, water droplets, and ice crystals. The meter measures the intensity of the light that is scattered and absorbed by these particles.

3. Signal Processing: The measured light intensity is processed to determine the visibility. This can be done using various algorithms that account for the light source intensity, the distance traveled by the light beam, and the attenuation due to the atmosphere.

4. Display and Output: The visibility reading is displayed on the meter's screen or outputted to a connected device, such as a computer or a dashboard in an airport control tower. Some meters also provide additional information, such as the rate of visibility change or warnings for reduced visibility conditions.

Visibility meters come in different forms, including handheld portable devices, fixed installations at airports and weather stations, and remote-sensing systems. 

Visibility meters are crucial for providing accurate and timely information about visibility levels, which is essential for weather forecasting, air traffic management, roadway safety, and environmental monitoring. visibility meters are essential tools for meteorologists, air traffic controllers, transportation authorities, and environmental scientists to monitor and manage visibility-related risks.

visibility sensors data sheet 

NBL-W-VS-Visibility-Sensor-Instruction-Manual.pdf