Research Group
"Optical Remote Measurements - Analysis of Atmospheric Processes with Optical Methods"

Temperature-Moisture-Aerosol Raman Lidar

Motivation

Routine observations of aerosol properties and meteorological conditions at the urban lidar site of Leipzig

Instrument

A seeded Nd:YAG laser emits light at wavelengths of 1064, 532, and 355 nm with an overall power of 1.6 J and a repetition rate of 30 Hz. A 15-fold beam expander reduces the beam divergence to less than 0.1 mrad. The backscattered light is alternatingly collected with a far-range telescope (1-m Cassegrain telescope) and a near-range telescope (10-cm Newton telescope). A 10-channel receiver separates the elastically backscattered signals at the three laser wavelengths and the Raman signals of nitrogen at 387 and 607 nm and of water vapor at 407 nm by the use of dichroic beamsplitters and interference filters. A polarizer discriminates the parallel- and cross-polarized components of the 532-nm backscatter signal. Two pure rotational Raman signals of nitrogen are separated by a double-grating monochromator. A Fabry-Perot interferometer (FPI) allows the suppression of the daylight background between the pure rotational Raman lines. All signals are detected by photomultiplier tubes and recorded in single-photon-counting mode.
From the detected signals, profiles of the backscatter coefficient at the three emitted wavelengths, of the depolarization ratio, as well as of the extinction coefficient and the lidar ratio at 355 and 532 nm are determined. Furthermore, profiles of water-vapor mixing ratio and temperature are derived. From these two quantities the relative humidity can be determined in the same scattering volume as the aerosol properties (Raman lidar principle).

Setup

(Just click on the picture to enlarge!

Temperature-Moisture-Aerosol Raman Lidar (stationary system)
Separation of backscattered light: elastic signals at 355, 532, 1064 nm vibration-rotation Raman signals of nitrogen at 387 and 607 nm vibration-rotation Raman signals of water vapor at 407 nm parallel- and cross-polarized components of the 532-nm signal
Separation of two rotational Raman signals with a Fabry-Perot interferometer and a double-grating monochromator for temperature measurements
Arrangement of optical fibers in the monofiber blocks of the double-grating monochromator
Derived parameters: Extinction coefficient at 355 and 532 nm Depolarization ratio at 532 nm Backscatter coefficient at 355, 532, and 1064 nm Lidar ratio at 355 and 532 nm Temperature Water-vapor mixing ratio Relative humidity

Cooperation

Implementation of the temperature channels (FPI + monochromator) by Yuri F. Arshinov, Sergej M. Bobrovnikov, and Ilya B. Serikov from the Institute for Atmospheric Optics, Siberian Branch of the Russian Acadamy of Sciences, Tomsk, Russia

Applications

• Longterm observation of aerosol properties in central Europe
  
• Air-mass modification processes over Europe
• Observations of long-range transport aerosols (Saharan dust, forest-fire smoke)
  
• Haze optical properties over Leipzig: 1990-1994 versus 2000-2003
• Vertical aerosol flux measurements in combination with the Doppler wind lidar
• Temperature measurements

Projects

• part of the German lidar network (1997-2000)
• part of EARLINET (since 2000)

Publications

Mattis, I., Ansmann, A., Althausen, D., Jänisch, V., Wandinger, U., Müller, D., Arshinov, Y. F., Bobrovnikov, S. M. and Serikov, I. B. 2002. Relative humidity profiling in the troposphere with a Raman lidar. Appl. Optics, 41, 6451-6462.

Arshinov, Y. F., Bobrovnikov, S. M., Serikov, I. B., Ansmann, A., Wandinger, U., Althausen, D. and Mattis, I. 2005. Realization of daytime operation of a pure rotational Raman lidar by use of a Fabry-Perot interferometer, Appl. Optics, 44, 3593-3603.

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