Remote Sensing of the Atmosphere by Resonance Raman LIDAR

Abstract

With our increased environmental awareness has come the need for technologies that can detect, identify and monitor pollutants and, where necessary, verify their destruction. This need is evidenced by the recent creation of the Clean Air Act Amendments (CAAA), of which the Title III-Hazardous Air Pollutants (HAP) amendments mandate the complete revision and expansion of the earlier Clean Air Act (CAA), section 112.1 As was pointed out by Grant, Kagann and McClenny,2 optical remote sensing technologies are expected to play a very important role in insuring that various facilities are in compliance with the Maximum Achievable Control Technology (MACT) standards for the reduction of HAP emissions that are called for in section 301 of Title III. Unfortunately, however, many of these technologies have varying detection and applicability characteristics which often dictate the conditions under which one can use the sensor to detect, identify or monitor a chemical species. Some of the advantages3-8 that a Raman-based pollution sensor possess are: (1) very high selectivity (chemical specific fingerprints), (2) independence from the excitation wavelength (ability to monitor in the solar blind region), (3) chemical mixture fingerprints are the sum of its individual components (no spectral cross-talk), (4) near independence of the Raman fingerprint to its physical state (very similar spectra for gas, liquid, solid and solutions), and (5) insensitivity of the Raman signature to environmental conditions (no quenching, or interference from water). The detection of atmospheric components using Raman backscattering of laser radiation dates back to the pioneering work of Leonard9 in 1967. In that study, he used a pulsed N2 gas laser at 337.1 nm to generate Raman return signals from N2 and O2.