{"id":13499,"date":"2022-11-10T20:32:10","date_gmt":"2022-11-10T10:32:10","guid":{"rendered":"https:\/\/www.lidarsolutions.com.au\/?p=13499"},"modified":"2025-06-20T16:31:33","modified_gmt":"2025-06-20T06:31:33","slug":"how-does-doppler-wind-lidars-work","status":"publish","type":"post","link":"https:\/\/www.lidarsolutions.com.au\/nz\/blog\/knowledge\/how-does-doppler-wind-lidars-work\/","title":{"rendered":"How do Doppler Wind LiDARs Work - NZ"},"content":{"rendered":"
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What is doppler effect?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Wind Lidars<\/a> are based on the theory of Doppler effect<\/a>. The following is an overview of LiDAR Solutions and what describes what is Doppler effect.<\/span><\/span><\/span><\/span><\/span><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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In 1842, Doppler, an Austrian mathematician and physicist, passed by the railway and a train passed him. He found that when the train came from a distance, the sound of the whistle became louder and the pitch increased, and when the train was leaving, the sound becomes weaker and the pitch lowers.<\/span><\/span><\/span><\/span><\/p>

Learn more from the video below – Brass band on train demonstrates Doppler effect<\/strong><\/span><\/span><\/span><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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This physical phenomenon has aroused great interest in Doppler<\/a>, and the following conclusions have been drawn after research.<\/span><\/span><\/span><\/span><\/span><\/span><\/p>

When the sound source moves toward the observer, the wavelength of the sound wave decreases (the frequency increases), so the pitch increases; when the sound source moves away from the observer, the wavelength of the sound wave increases (the frequency decreases), so the pitch decreases as demostration below:\u00a0<\/span><\/span><\/span><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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The change in pitch is related to the ratio of the relative velocity to the sound velocity between the source and the observer. The larger the ratio, the more significant the change, which is the “Doppler effect”, and the resulting frequency change is called the Doppler shift.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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The mathematical expression of the Doppler effect:<\/p>

The frequency relationship between the observer and the source is<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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F1<\/span><\/span><\/strong> is the observed frequency;<\/span><\/span>
F<\/span><\/span><\/strong> is the original emission frequency at which the emission originates from the medium;<\/span><\/span>
V<\/span><\/span><\/strong> is the traveling speed of the wave in the medium;<\/span><\/span>
V0<\/span><\/span><\/strong> is the movement speed of the observer. If it is close to the emission source, the front operation symbol is +, otherwise, it is -, and the observer is stationary, it is 0;<\/span><\/span>
Vs<\/span><\/span><\/strong> is the moving speed of the emission source. If it is close to the observer, the front operation symbol is – sign, otherwise, it is + sign.<\/span><\/span><\/p>

The Doppler effect applies not only to sound waves, but also to radio waves and light waves.<\/span><\/span><\/strong><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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Working Principle of Doppler Wind LiDAR<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Wind LiDAR<\/a> has many complexities. There are many aerosol particles in the air, which refer to solid particles and liquid particles uniformly dispersed in the atmosphere, such as fog, smoke, haze, fine dust and smog. The wind-measuring lidar emits a laser beam into the air, and when the laser irradiates these aerosol particles, it will reflect, and the reflected wave of the moving particles will have a Doppler frequency shift. The frequency shift is the difference between the frequencies of the transmitted wave and the reflected wave.<\/span><\/span><\/span><\/span><\/p>

In the figure below, the angle between the laser wave emitted by the lidar and the vertical line on the ground is \u03c6. The laser will be reflected when it encounters aerosol particles, and the lidar will process the reflected wave after receiving it. The distance L between the aerosol particle and the radar is obtained by the time difference between the aerosol particle of the transmitted wave and the received wave<\/span><\/span><\/p>

The height of the aerosol particle h=L\u00b7cos\u03c6<\/span><\/span><\/span><\/span>
The velocity Vs of the aerosol particles relative to the radar is calculated by the frequency shift \u0394f of the transmitted wave and the received wave,<\/span><\/span><\/span><\/span>
The horizontal moving speed of aerosol particles V=Vs sin\u03c6<\/span><\/span><\/span><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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The internal structure of the doppler Wind monitoring LiDARs:<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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The horizontal moving speed V of aerosol particles is only the speed toward the vertical line z of the lidar, not the actual wind direction and speed. To get the actual wind direction and wind speed,\u00a0 LiDAR needs to send more laser beams into the air and reconstruct wind speed of wind fields.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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It may seem simple, but it is actually very complex. The atmosphere is full of aerosol particles, and the reflected waves are very complex as well. It is a superposition of a large number of reflected waves. How to select the desired wave from the massive clutter is very complicated. Technology can only be solved by using precise analog and massive digital processing technology. Therefore, the current cost of lidar wind measurement is still very expensive, but with the improvement of device performance, the price will gradually decrease.<\/span><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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Types of doppler wind measurement lidar<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Molas B300- Onshore Wind Measurement<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Key Features<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Bankable: <\/span><\/span><\/strong>fully classified by DNV-GL against <\/span><\/span>DNV-GL<\/a> according to IEC61400-12-1 ed2, and verified by Windguard<\/a> and DTU;\u00a0<\/p>

Measuring distance:<\/span><\/span><\/strong> from 30 to 300m, with 12 configurable heights;<\/span><\/span><\/p>

Robust design:<\/span><\/span><\/strong>\u00a0State-of-Art design and manufacturing, with IP67 protection which can be deployed in harsh environment;<\/span><\/span><\/p>

Complex terrain support:<\/span><\/span><\/strong> complex wind measurement data re-construction with no extra cost<\/span><\/span><\/p>

Can operation in various site condition:<\/span><\/span><\/span><\/span><\/strong> proven experiences in sites with high altitude, high\/low temperature & heavy rainfall area.\u00a0<\/span><\/span><\/span><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t

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Applications - Molas B300 Doppler Wind Measurement LiDAR System<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Onshore wind farm development projects:<\/strong><\/p>