Laser Remote Sensing of the Atmosphere

We will discuss two active remote-sensing techniques for the atmosphere — the long-path absorption technique and the lidar technique. However, we will first consider a passive technique, in which lasers play an important part in the detection scheme. This optical heterodyne technique is even more frequently used for signal recovery in connection with the active optical remote-sensing methods. The field of laser monitoring of the atmosphere is covered in several monographs and articles [10.70-10.76]. 

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D. K. Killinger, N. Menyuk Laser remote sensing of the atmosphere. Science 235, 37 (1987)... 

P. Rairoux, H. Schillinger, S. Niedermeier, M. Rodriguez, F. Ronneberger, R. Sauerbrey, B. Stein, D. Waite, C. Wedekind, H. Wille, L. Woste, Remote sensing of the atmosphere using ultrashort laser pulses, Applied Physics B 71, 573-580 (2000)... 

At V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry a laser IR spectrometer has been developed in co-operation with the International Laser Center of Moscow State University. It is designed for the remote sensing of various atmospheric pollutants by the long path IR-spectroscopy in a 3 mcm atmospheric window [8,9]. the functional scheme of this device is presented on Fig.4. 

The format is as before, with the addition of one small section on the use of lasers in isotope separation and remote sensing of atmospheric pollutants. Emphasis is again placed upon the physical fates of excited molecules, and in particular on studies of isolated molecules. 

In many of the sophisticated experimental techniques applied to photophysical problems, the rapid development of the laser has enabled results to be obtained which were unheard of only a few years ago. These developments have been described adequately in previous and current volumes, but there are two applied uses of the laser which have not yet received significant attention, and to which readers attention is drawn by this short extra section this year. The first is concerned with the remote sensing of atmospheric pollutants. The methods available to achieve this object can be classified as passive, for example the heterodyne detection of thermal emission,209 or active, involving some radiation source. The means of attenuating the intensity of such a source are listed below. 

As noted earlier, fused silica optical fiber is used for remote NIR measurements. The same type of fiber optic probe can be used for Raman spectroscopy, and enables remote measurement of samples and online process measurements. In situ reaction monitoring by Raman spectroscopy has been used to study catalytic hydrogenation, emulsion polymerization, and reaction mechanisms. Remote sensing of molecules in the atmosphere can be performed by Raman scattering measurements using pulsed lasers. 

The various techniques of Raman scattering that enable laser-based diagnostics of technical combustion processes as well as species identification on the micrometer scale or remote sensing of molecular species and pollutant in the atmosphere. 

In Fig.6.71 different passive and active remote-sensing techniques are illustrated. The selective reflection of solar radiation from the earth s surface, the absorption or the thermal emission of the atmosphere can be studied with passive techniques. Active techniques frequently make use of laser or microwave radiation. The transmission or scattering of such radiation can yield information on the atmosphere or the land and sea surface. 

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