Simulation studies have been carried out to analyze the performance of a Differential Absorption Lidar (DIAL) system for the remote detection of a large variety of toxic agents in the 2-5 μm and 9-11 μm spectral bands. Stand-alone Graphical User Interface (GUI) software has been developed in the MATLAB platform to perform the simulation operations. It takes various system inputs from the user and computes the required laser energy to be transmitted, backscattered signal strengths, signal-to-noise ratio and minimum detectable concentrations for various agents from different ranges for the given system parameters. It has the flexibility of varying any of the system parameters for computation in order to provide inputs for the required design of proposed DIAL system. This software has the advantage of optimizing system parameters in the design of Lidar system. As a case study, the DIAL system with specified pulse energy of OPO based laser transmitter (2-5 μm) and a TEA CO<sub>2</sub> laser transmitter (9-11μm) has been considered. The proposed system further consists of a 500-mm diameter Newtonian telescope, 0.5-mm diameter detector and 10-MHz digitizer. A toxic agent cloud with given thickness and concentration has been assumed to be detected in the ambient atmospheric conditions at various ranges between 0.2 and 5 km. For a given set of system parameters, the required energy of laser transmitter, power levels of the return signals, signal-to-noise ratio and minimum detectable concentrations from different ranges have been calculated for each of these toxic agents.
One of the main functions of a Doppler Lidar system is to measure the atmospheric wind speed and direction. It is done by measuring the Doppler shift in frequency of the backscattered laser beam. A frequency stabilized Nd: YAG laser source operating at its fundamental wavelength of 1064 nm will be used in the proposed incoherent detection system. Edge technique is employed along with a high-resolution optical filter in this system to achieve high accuracy in the measurement of wind velocity. The performance of Doppler lidar system is estimated with realistic parameters. Analysis of the uncertainty in wind measurement is made by considering factors like lidar return signal levels, laser spectral width, etalon filter pass band (FWHM) etc. An accuracy of 0.25 m/s has been achieved in the wind speed up to an altitude of 5 km with 15-m range resolution in the proposed ground based Doppler Lidar system.
Computer simulations have been carried out to optimize the IR Differential Absorption Lidar (DIAL) system in order to measure the gaseous pollutants released by the industries. The concentration of the gaseous pollutants due to elevated sources is computed using the Gaussian dispersion model. For given atmospheric conditions and stack physical parameters, the downwind distance (x) at which the SO<sub>2</sub> reaches the safe limit of its toxicity has been computed at given other two coordinates (y, z) with respect to chimney. The gaseous pollutants released by the industries will be effectively monitored by the proposed DIAL system, which will be placed at New Delhi (28.35 degrees N, 77.12 degrees E), India. The performance of the Lidar has been optimized based on the various system parameters incorporating the atmospheric conditions and stack physical parameters. Further, the backscattered return powers at on- & -off line wavelengths, the required energy to be transmitted and the position at which the lidar system should be posted have been computed in order to monitor SO<sub>2</sub>.