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

Six-Wavelength Lidar

Motivation

Observations of aerosol properties and meteorological conditions in field campaigns all over the world

Instrument

Two seeded Nd:YAG lasers and two Titanium:Sapphire lasers emit light at wavelengths of 1064, 800, 710, 532, 400 and 355 nm with an overall power of twice 1.6 J and a repetition rate of 30 Hz. A 10-fold beam expander reduces the beam divergence to less than 0.1 mrad. The backscattered light is collected with a 53-cm Cassegrain telescope. A 14-channel receiver separates the elastically backscattered signals at the six laser wavelengths and the Raman signals of nitrogen at 387 and 607 nm and of water vapor at 660 nm by the use of dichroic beamsplitters and interference filters. A polarizer discriminates the parallel- and cross-polarized components of the 710-nm backscatter signal. Two pure rotational Raman signals of nitrogen are separated by a double-grating monochromator. All signals are detected with photomultiplier tubes and recorded in single-photon-counting mode or the photomultiplier is operated in current mode.
From the detected signals, profiles of the backscatter coefficient at the six 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 picture to enlarge!
Six-wavelength aerosol lidar (for field campaigns)	Take a little tour by clicking on the pictures!
Separation of backscattered light: elastic signals at 355, 400, 532, 710, 800, and 1064 nm vibration-rotation Raman signals of nitrogen at 387 and 607 nm vibration-rotation Raman signals of water vapor at 660 nm pure rotational Raman signals at 532 nm parallel- and cross-polarized components of the 710-nm signal	Take a little tour by clicking on the pictures!
Separation of two rotational Raman signals with a double-grating monochromator for temperature measurement
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 710 nm Backscatter coefficient at 355, 400, 532, 710, 800, and 1064 nm Lidar ratio at 355 and 532 nm Temperature Water-vapor mixing ratio Relative humidity

Cooperation

Implementation of the temperature channels (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

Projects

• ACE-2
• LACE 98
• INDOEX
• SAMUM