Lidar
EARLINET QUICKLOOKS - MPLNET DATA - CALIPSO DATA - LOA QUICKLOOKS
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LIDAR (LIght Detection And Ranging) is a radar system using ultraviolet, visible or near-infrared light instead of microwaves or radio waves. Very short laser pulses of light are sent into the atmosphere and partially scattered back to the lidar by gases and aerosols in the air. The position, concentration and some information on the properties of the scatters are determined from the backscattered energy and the time to return to the lidar. The aerosol lidar systems estimate vertical profiles of particulate from the backscatter profiles. |
Comparison of backscatter at different wavelengths provides some indication of particle size. Finally, if polarized light is used, the non-spherical character of particles can be determined: since dust particles are usually less spherical than other aerosol types, the method allows distinction between mineral dust and other pollutants.
Lidar technology can be divided into elastic systems that measure at the frequency of the emitted light and non-elastic systems that monitor Raman-shifted frequencies. The fundamental problem of elastic lidars is that clear-air scattering is not negligible in the near-visible range. This forms a problem of having one measured variable (the returned energy) and two unknowns: the particulate optical extinction and backscatter coefficients. This dependence necessitates the prescription of the ratio between both coefficients, that is, the lidar ratio. However, the lidar ratio connects two optical quantities that both depend on the wavelength of the incident light, the refractive index, and the aerosol size distribution.
There are several lidar networks. Two of them can be highlighted in our geographical domain:
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European Aerosol Research Lidar Network, EARLINET. It was the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on a continental scale. |
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NASA Nicro-Pulse Lidar Network, MPLNET. It is a federated network of Micro-Pulse Lidar (MPL) systems designed to measure aerosol and cloud vertical structure continuously, day and night, over long time periods. |
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The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), launched on April 28, 2006, combines an active lidar instrument with passive infrared and visible imagers to probe the vertical structure and properties of thin clouds and aerosols over the globe. CALIPSO is a joint U.S. (NASA) and French (Centre National d'Etudes Spatiales/CNES) mission. DATA |
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Since 2006, the Atmospheric-Optics Laboratory (LOA: Lille-1 University / CNRS) started developping the basis of a small LIDAR network composed of single wavelength (532 nm) elastic backscatter CIMEL micro-LIDAR. QUICKLOOKS |