Infrared LIDAR Applications in Atmospheric Monitoring
Environment: Trace Gas Monitoring
Published Online: 15 SEP 2006
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
Orr, B. J. 2006. Infrared LIDAR Applications in Atmospheric Monitoring. Encyclopedia of Analytical Chemistry. .
- Published Online: 15 SEP 2006
The acronym LIDAR stands for light detection and ranging, an optical analog of RADAR (radio detection and ranging). The conventional version of LIDAR requires a laser transmitter to launch short pulses of coherent light, which are scattered from atmospheric targets of interest back to an optical receiver, with a time delay that is determined by the range of the target. Optical phenomena in the Earth's atmosphere (e.g. Rayleigh scattering, Raman scattering, Mie scattering, refraction, and resonant absorption) contribute to the amplitude of optical signals returning to the receiver and their characteristic wavelength dependence allows us to measure the concentration and velocity distributions of different atmospheric molecules and aerosol particles. LIDAR backscattering in the infrared (IR) region, on which this article concentrates, is well suited to detecting aerosols (as in clouds or industrial particulate emissions). IR DIAL (differential absorption LIDAR), a variant in which two wavelengths are used simultaneously to separate resonant molecular signals from background, enables most molecular species to be monitored by means of their IR absorption spectra. A closely related approach comprises long-path IR laser absorption, with retro-reflection from a topographic target (e.g. a strategically located mirror); this sacrifices optical range information but gains sensitivity because it integrates over all molecules in the optical column between the transmitter/receiver and the reflector. Such techniques are vitally dependent on pulsed IR laser technology.