LIDAR technology: Remote sensing of the atmosphere and flying objects using lasers
LIDAR (LIght Detection and Ranging) is based on the same principle as radar, but uses laser light instead of radio waves. In this technology, a pulsed laser light is emitted into the atmosphere, and the light is reflected back from the atmosphere, clouds and aerosols is measured, making it possible to measure trace components present in the air, as well as the distributions of water vapor, wind direction and velocity, temperature, aerosol density and others.
LIDAR is a compact device and is almost only one means, which provides a means for achieving remote sensing of the upper atmosphere from the ground, without launching a sonde or using an aircraft.
LIDAR can measure quantities, which is difficult to do using direct sampling, and eliminates the process of sampling species unlike an ordinary chemical analysis.
When LIDAR is directed into the atmosphere at an incline, multiple points can be measured from the same ground point. A mobile LIDAR can be transported to various locations to monitor various targets.
The LIDAR measurements require extremely little time for analysis, and the data is obtained in very close to real time. Additionally, because of the capability of continuous measurement, the data can be easily generated in a graph or map format. |
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Concept of LIDAR
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Laser technology cultivated by Hamamatsu Photonics over many years is effectively used in the development of lasers technology relating to the LIDAR. Moreover, Hamamatsu Photonics photomultiplier tubes are being effectively used in detecting very weak return signal from materials in the atmosphere. |
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Outlook of LIDAR used for aerosol measurement
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There are a number of different types of LIDAR, depending on the principle of measurement for monitoring object. At Hamamatsu Photonics, our particular focus is on developing "Mie scattering LIDAR" for measuring aerosols in the lower atmosphere.
Typical LIDAR methods
Type of LIDAR |
Measurement principle |
Application |
Mie scattering LIDAR |
Mie scattering of laser light caused by aerosols, etc. |
Measurement of aerosols in the lower atmosphere |
Rayleigh scattering LIDAR |
Rayleigh scattering of laser light caused by molecules, etc. |
Measurement of the density and temperature of the air in the middle atmosphere |
Raman scattering LIDAR |
Raman scattering (a kind of inelastic scattering) of the laser light caused by molecules |
Measurement of water vapor, high density air pollutant from exhaust. |
Fluorescent LIDAR |
Fluorescent measurement from excited gas molecules |
Identification and density measurement of middle atmospheric molecules |
Differential absorption LIDAR |
Absorption of laser light caused by molecule |
The identification and measurement of molecular density |
Doppler LIDAR |
Measurement of the wavelength shifts caused by the Doppler effect of Mie scattered light |
Measurement of direction and velocity of wind |
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Conventional LIDAR units required frequent adjustments and temperature controlling equipment in order to operate continuously. It was also necessary to adjust the optical axis and replace the flash lamp periodically. This meant that maintenance had to be carried out frequently.。
At Hamamatsu Photonics, we're making efforts to develop a LIDAR unit that will not only offer better performance, but will also improve weaknesses in conventional systems and will be capable of operating continuously with only minimum maintenance. If we can realize a LIDAR unit that's easy to transport and to handle even without special technology, it will open a broader spectrum of applicatios, such as being used for weather and environmental observation at local government communities.
Hamamatsu Photonics is working together with Chiba University on LIDAR research and technology development. Here, we introduce some examples of LIDAR observation.(Photo provided by courtesy of Prof. Nobuo Takeuchi, Director, Center for Environmental Remote Sensing, Chiba University)
Observation of Asian dust* (March 12, 2003)
On this particular day, an Asian dust was observed even in Chiba area, Japan (in the vicinity of 4 km).
*Asian dust is fine sand originated by strong wind at the desert area in China.
Observation of Asian dust
Aerosol fallout: Observation of aerosol fallout and a second layer of aerosols
An example of observation of vigorous downward aerosol motion due to descending air flow.
Aerosol fallout
Observation of rain clouds: Descending rain clouds and prediction of precipitation
Rain clouds descend gradually from a height of around 2 km, with the circumstances from the onset to the cessation of precipitation being observed..
Observation of rain clouds
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