How is visibility determined in an observation?

Overview of visibility measurement techniques and their applications

In the broad field of meteorology, visibility, as a crucial indicator, not only affects daily transportation, but also is the cornerstone of aviation and navigation safety. With the progress of science and technology, the measurement of visibility has evolved from relying on the observer's visual judgment to the present automated era, which is highly dependent on precision instruments. This paper will discuss the application and importance of modern and traditional methods in visibility observation.

 1. Traditional and Modern Methods of Visibility Measurement

 1.1 Manual Observation Method

Although the traditional manual observation method is gradually replaced by modern instruments, it still plays an important role in specific situations. During daytime, the observer usually chooses a place with a wide field of view and a contrasting background for observation. Target objects may be distant mountains, buildings, etc. With the increase of dust and water vapor particles in the atmosphere, the form and color of the target are gradually blurred, and the observer will estimate the visibility value based on the visibility and distance of the target.

For night observation, lights are the main object of observation, especially in areas with heavy traffic, such as seaports and airports, where lighthouses and navigation lights become the main visibility reference objects. The advantage of manual observation is that it can combine the field environment and experience for measurement, but its disadvantage is limited by the subjective factors of the observer, and the measurement accuracy is relatively low.

 1.2 Instrumental observation method

With the continuous development of meteorological technology, instrumental observation method has become the mainstream of modern visibility measurement. Common instruments are transmission visibility meter and scattering visibility meter. These instruments are able to provide fast and stable visibility values through accurate optical measurements, and play an important role especially in critical aviation and shipping fields.

- Transmissive Visibility Meters: Transmissive visibility meters work by emitting a parallel beam of light outward from a light source. When the light passes through the atmosphere, it is attenuated by dust and water vapor particles in the air. The instrument calculates the visibility value according to the degree of attenuation. This type of equipment is widely used in places where high precision visibility monitoring is required, such as airport runways.  

- Scattering Visibility Meter: Scattering Visibility Meter works by utilizing the principle of light scattering. Scattering occurs when a light source hits tiny particles in the air. The instrument receives and analyzes this scattered light to determine visibility. Due to its simple structure and flexible operation, the scattering visibility meter is widely used in weather stations, waterways and highways.

 2. Working Principle and Advantages of NBL-W-VS Visibility Meter

NBL-W-VS visibility meter is a new generation of visibility measurement equipment designed based on aerosol front scattering principle. As a development product after the transmission visibility meter, it has the characteristics of high efficiency and accuracy, and has been applied in many fields, such as weather stations, remote automatic weather stations, airports, highways, airways and large ships and other transportation departments.

 2.1 Working Principle of NBL-W-VS Visibility Meter

The working principle of the NBL-W-VS visibility meter is based on the measurement of front-scattered light. A transmitter emits pulsed infrared light, which is forward-scattered by aerosol particles in the atmosphere. The receiver detects the scattered light and converts it into electrical signals, which are then processed by a microprocessor control unit to finally calculate the visibility value.

In contrast to transmission visibility meters, which measure the attenuation coefficient of light, scattering visibility meters assess visibility by measuring the intensity of pulses of light scattered forward by particles in the atmosphere. This method is particularly effective for scenarios where the visibility is less than 100 kilometers, especially in situations such as haze, smog or precipitation, and provides a more accurate reflection of visibility.

 2.2 Structural Composition of Visibility Meter (Visibility Sensor)

NBL-W-VS visibility meter is mainly composed of the following parts:

- Transmitter: Built-in laser tube, transmits laser signal through a fixed angle.

- Receiver: Built-in photosensitive receiver for receiving scattering signals triggered by suspended particles in the air.

- Microprocessor control unit: Built-in microprocessor controller responsible for sampling and calculating visibility values. The calculated real-time visibility value is transmitted to the data acquisition terminal via RS-485 interface.

 2.3 Application and Advantages of Visibility Meter

The advantages of NBL-W-VS visibility meter are mainly reflected in the following aspects:

- High accuracy: Since the instrument can accurately measure the intensity of forward scattered light, it can effectively provide accurate visibility data, especially applicable to the situation where there are suspended particles in the atmosphere and precipitation and other influences.

- Strong stability: Compared with manual observation, the instrument measurement is not affected by individual visual acuity differences and subjective factors, which ensures the consistency and reliability of the data.

- Widely used: The equipment can be used not only in weather stations, airports and other places, but also in highways, airways and large ships and other transportation sectors, providing strong protection for traffic safety.

 3. System integration and data application

Modern visibility meters, such as NBL-W-VS, not only require high-precision measurements, but also need to have the ability to communicate efficiently with the monitoring center. With DC12V power supply and RS485 communication cable, the visibility meter not only provides real-time data, but also allows remote configuration and status monitoring through built-in commands, which greatly improves the efficiency of data processing and system flexibility.

Conclusion:

The determination of visibility is a core aspect in meteorological observation, which reflects the perfect combination of science and technology and traditional methods. The high precision and automation of modern instruments, supplemented by the experience of manual observation, together build a comprehensive and reliable visibility monitoring system.The emergence of visibility monitoring equipment, such as NBL-W-VS visibility meter, signifies that the meteorological observation technology has stepped into a new era, which provides solid scientific and technological support for safeguarding public safety and promoting the smooth operation of transportation.

visibility sensors data sheet 

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