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What is the principle of visibility sensor?

Time:2023-11-17 11:10:10 Popularity:34

Visibility sensors provide measurements related to meteorological visibility. The sensors are designed based on the aerosol forward scattering principle and are a new generation of meteorological visibility monitoring equipment developed following the transmission visibility meter.

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The visibility meter (visibility sensor) consists of a light transmitter, a light receiver and a microprocessor controller and other major components. The transmitter emits infrared pulses of light, the receiver simultaneously detects the intensity of pulses of light scattered forward by aerosol particles in the atmosphere, and all the measurement information is collected by the microprocessor controller and transformed into Meteorological Optical Range (MOR) through the algorithm of specialized mathematical model.

Principle of operation of visibility sensors:

The principle of a visibility sensor is based primarily on optical principles. It uses an infrared light source and the principle of light scattering to measure visibility. The sensor contains a transmitter and a receiver. The transmitter emits an infrared light beam, which is scattered and absorbed by particles in the atmosphere. The receiver receives the scattered and absorbed beam and converts the signal into a visibility value.

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During the operation of the sensor, the light beam from the transmitter encounters particles such as fog, smoke, and dust in the atmosphere, which scatter the light. Based on the ratio of the intensity of the scattered light to the intensity of the received light, the value of visibility can be calculated. When there are more particles in the atmosphere, the stronger the scattered light is and the weaker the intensity of the light received, the lower the visibility value will be.

To improve the accuracy of the measurement, visibility sensors also take into account the influence of other factors, such as temperature and humidity. These factors affect the concentration and particle size distribution of particulate matter in the atmosphere, which in turn affects the visibility measurement. Therefore, these factors are taken into account in the design and algorithms of the sensors, and corresponding corrections and modifications are made to improve the accuracy and reliability of the measurements.

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The visibility meter (visibility sensor) has all the performance characteristics of a forward-scattering instrument, which is realized by measuring the forward-scattered light emitted by suspended particles in a sampling area of less than 90 degrees; the sampling area of the visibility meter is determined by the intersection of the transmitter's transmitting optical path and the receiver's receiving optical path. Obviously, it differs from the total extinction coefficient measured by a transmissometer in that a forward scatterometer measures only the scattering coefficient at a certain angle, i.e., a narrower scattering angle near the central forward scattering angle.

It is generally accepted that the calculation of daytime and nighttime visibility requires the measurement of the total extinction coefficient, not the angular scattering coefficient, and it is therefore necessary to show that the angular scattering coefficient is, under certain conditions, in definite proportion to the total atmospheric extinction coefficient, which consists of the sum of the scattered and absorbed rays over the entire range.

In visibility measurements of less than 100 km, suspended particles such as fog, smoke, haze, dust or sand, and various types of precipitation determine the atmospheric extinction of visible and near-visible light, and scattering by molecular matter comes into play at distances of more than 100 km; the absorption by suspended particles and precipitation is negligible in comparison with their scattering.

For these reasons, the total scattering coefficient can be equal to the total extinction coefficient at visibility less than 100 km.

Visibility sensors can be widely used in weather stations, remote automatic weather stations and transportation departments such as airports, highways, airways and large ships.

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