Abstract
A powerful two-frequency lidar system using polarized beams has been developed at YerPhI. The system is completed with laser beam polarization changers and nitrogen and water Raman channels for investigation of the influence of atmospheric electric fields on the elastic and Raman backscattered beams polarization. At present, the system is being tuned for measuring vertical atmospheric backscatter profiles of aerosols and hydrometeors, analyze the depolarization ratio of elastic backscattered laser beams and investigate the influence of external factors on the beam polarization. Laser light that is reflected from the air and from clouds carries information on density profiles, aerosols and electrical fields. Applications of this system will be the investigation of the electrical state of the atmosphere during thunderstorms [1-3] on Mt Aragats, and, possibly the monitoring of the atmosphere at the site of the upcoming Cherenkov Telescope Array (CTA). CTA is expected to provide unprecedented sensitivity for gamma ray detection in the energy range of 30 GeV to 300 TeV. To fully exploit the potential of the telescope system it is important to characterize the optical and electrical properties of the atmosphere. A lidar system for the continuous monitoring of the atmosphere is the tool of choice.
Highlights
The LIDAR technique basicsEarth atmosphere, including suspending aerosols inside, have a variety of impacts which directly affect the radiative balance of the Earth–atmosphere system through scattering and absorption
A powerful two-frequency lidar system using polarized beams has been developed at YerPhI
The Laser Emitter (LE) is equipped with motorized positioning system of polarization optics, by means of which its output beam polarization can be remotely changed for both wavelengths of 1064 nm and 532 nm, including: both parallel linear horizontal or vertical; both parallel linear 45 degrees; linear and circular etc
Summary
Earth atmosphere, including suspending aerosols inside, have a variety of impacts which directly affect the radiative balance of the Earth–atmosphere system through scattering and absorption. The aerosols, being the most variable component in the atmosphere, need to be constantly monitored as they reflect the solar radiation at a daytime to decrease the overheating of the Earth surface and retain the infrared near the ground in the night time. The polarization LIDAR technique has the unique ability to discriminate between spherical and irregular particles and identify the type of atmospheric aerosols because of its sensitivity to particle shape [4]. One of the most useful experimental techniques involves the use of a linearly polarized lidar output and a receiver capable of simultaneously measuring the backscattered light two polarization components oriented parallel (P ) and perpendicular (P⊥) to the direction of the laser beam polarization axis. The measured data by means of the LIDAR System can be written as: P(R) R2 = β(R)exp(−2αR) KPL δ(R) = P⊥(R) P (R)
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