Theoretical Analysis of a Multiwavelength Differential Absorption Lidar System for Range-resolved Detection and Concentration Measurement of Some Pollutants in the Atmosphere

摘要

Differential Absorption Lidar (DIAL) techniques are advantageously used these days for detecting and measuring very low concentration levels of pollutants up to several kilometres in the atmosphere. In this paper, a theoretical study has been carried out to simulate the performance of a multiwavelength DIAL system. Nitrogen dioxide (NO_2), sulphur dioxide (SO_2) and methane (CH_4) dispersed in the atmosphere, have been taken as examples of the pollutants. It has been shown that a given lidar system cannot detect any of these pollutants at a certain distance if its average concentration is below a certain value (N_(min)). It has also been shown that if the average concentration level of a given pollutant is above a certain value (N_(max)) at a particular distance, this value cannot be detected for a given lidar system although its identity can still be determined. Further, for some typical parametric conditions, the required energy levels of the laser to detect specific concentrations of these pollutants at different distances have been computed. Power levels of the return signals from different ranges have also been calculated for each of these pollutants for a given value of the laser transmitter energy.