Laser-Raman radar ?Laser-Raman scattering methods for remote detection and analysis of atmospheric pollution

Abstract

This paper reviews the recent progress of the laser radar method, providing single-ended and range-resolved means for remote detection and analysis of various molecular species in the polluted as well as ordinary atmosphere, based on the existence of their Raman backscattering; simply called the laser-Raman radar method. A brief description is given of the operational principle including the basic concept and fundamental characteristics of this scheme, along with critical discussions of their advantages. The differential backscattering cross section and the spectral distribution of Raman scattering of molecular species present in the atmosphere are discussed and summarized from the practical view-point for providing molecular density evaluation and interference-free detection. After presenting experimental approaches of the laser-Raman scheme to show the feasibility of in-field monitoring and analysis of chemical species in various air conditions, the estimation of molecular concentrations is performed from observed Raman spectra. Analytical discussions on the minimum detectable concentration and the range detectivity are also presented to indicate the present capability and limitation of this laser-Raman technique. The potentiality for further progress in resonance Raman scattering for range-resolved measurement of dispersed pollutants in ambient air is pointed out.

Remote Monitoring of Air Pollutant Emissions from Point Sources by a Mobile Lidar/Sodar System

“…Lidars were used to monitor pollution in oil smoke plumes as early as 1972, 1 and commercial pollution-monitoring systems have been constructed since 1980. 2,3 With the differential absorption lidar (DIAL), two laser pulses with different wavelengths are emitted several times per second.…”

Observations of water vapor mixing ratio profile and flux in the Tibetan Plateau based on the lidar technique

“…The S branch ( υ = 1, J = +2) and O branch ( υ = 1, J = −2) are well separated in energy and appear as sidebands on the either side of the Q branch (Inaba and Kobayasi, 1972). The cross section of nitrogen in Q branch is about 10 −30 cm 2 sr −1 , which is 2 orders of magnitude bigger than the cross section in S and O branch (about 10 −32 cm 2 sr −1 ).…”

“…According to the selection rule for vibrational transitions (Inaba and Kobayasi, 1972;Inaba, 1976;Demtröder, 2005Demtröder, , 2013, the change of the vibrational quantum number is υ = 0, ±1, ±2, . .…”

“…The process of Raman scattering is characterized by a wavelength shift of the scattered radiation in respect to the exciting wavelength. The shift is uniquely associated with the internal transitions between the rotational-vibrational energy levels of the molecules (Inaba and Kobayasi, 1972;Inaba, 1976;Demtröder, 2005Demtröder, , 2013 and is used for identification of the scattering molecules. Because of the advantages of the high power laser source, the vertical detection range of the Raman lidars can extend to 7 km and throughout the troposphere (Whiteman et al, 1992;Vaughan et al, 1988;Goldsmith, 1998;Leblanc et al, 2008;Dinoev, 2009;Dinoev et al, 2013).…”

A broadband lidar for the measurement of tropospheric constituent profiles from the ground

“…Such criteria are achieved by conventional differential absorption lidar (DIAL) and Raman lidar systems. However, the species obtainable by using altitude-resolved vibrational Raman lidar are at present restricted by the extremely small Raman cross sections of most molecules [Inaba and Kobayasi, 1972]. A consequence of this restriction is that only in the study of atmospheric water vapor have significant advances been made [Melfi' et al, 1969;Melfi' and Whiteman, 1985;Grant, 1991;Eichinger et al, 1993].…”