Multiple-scattering effects can severely influences ground-based lidar measurements when the optical depth is not negligible such as in presence of fog or clouds. This problem can be faced both analytically and by Monte Carlo methods, although as usual the analytical techniques require several simplifications about the microphysical mechanisms whereas Monte Carlo simulation constitutes a more direct approach. In this paper, we discuss an iterative Monte Carlo method to simulate photon multiple scattering in optically dense media. Our results show that it is possible to correct for the multiple scattering influence both extinction and backscattering coefficients obtained by Raman lidar. In particular, for the typical cirrus cloud, the presence of the multiple scattering can lead to an underestimation of the extinction coefficient as large as 100% whereas the backscattering coefficient is almost unaffected by such process. This in turn evidences the strong dependence of the lidar ratio on the multiple-scattering effect.
This paper is presented to give a general description of the ORACLE project and of the technology development results obtained to date. ORACLE is a feasibility study of a fully automated differential absorption lidar for global measurements of tropospheric and stratospheric ozone and aerosols with high vertical and horizontal resolution. The proposed program includes both novel technology demonstrations and obtaining scientific data from spacecraft. These data are needed to address key issues in atmospheric research including the depletion of stratospheric ozone, global warming, atmospheric transport and dynamics, tropospheric ozone budgets, atmospheric chemistry, and the atmospheric impact of hazards. Only a space-based lidar system can provide the required spatial resolution for ozone and aerosols in both the stratosphere and the troposphere on a global scale at all required altitudes. To deliver these data, the most novel technologies such as all-solid-state lasers, photon-counting detectors and ultra-lightweight deployable telescopes must be employed in the mission payload.
This paper presents the results of a lidar campaign for aerosol and smoke plume studies carried out in collaboration with the Ministry of Environment of the Province of Ontario at the industrial complex in the city of Hamilton. The aim of the study was to apply lidar remote sensing to measure simultaneously emissions from different sources and determine the potential of lidar for tracking and differentiating plumes from various industrial processes. This study was carried out with the scanning lidar system of the Canadian Defense Research Establishment (1064 nm, 60 mJ, 100 Hz, dual polarization). The scanning lidar system was successful in providing coverage in azimuth ((phi) ) and elevation ((Theta) ) to map effluent plumes in 3-D from a range of over 5 km targeting major individual industrial sites. From 5 km range, for differentiating the plumes within one industrial complex, the highest resolutions (Delta) (phi) equals 0.05 degrees and (Delta) (Theta) equals 0.03 degrees available were necessary. To understand the dynamic behavior of plumes, time series scans were required which are a key to determining sources of Black Fallout and fugitive emissions that deposit particulate matter in the Hamilton area. Examples of relative plume strengths as demonstrated by the lidar are also discussed.
Lidar observations of stratospheric ozone, aerosol and temperature have been carried out at Toronto (43.8 N, 79.5 W) since 1989 and during winter months at the Arctic Stratospheric Observatory (AStrO) at Eureka (80 N, 86 W) since 1992. The Raman DIAL (Differential Absorption Lidar) systems utilized at both observatories are briefly described and the measurements are discussed. The measurements of AStrO are discussed in relation to the dynamics of stratospheric polar vortex and the presence of polar stratospheric clouds (PSC). Results from the winters of 1994/95 and 1995/96 indicate very low polar stratospheric temperatures, capable of inducing PSCs and exhibit an appreciable ozone depletion.
A new Arctic stratospheric observatory (AStrO) has been established at Eureka (80 degree(s)N, 86 degree(s)W) in northern Canada. This observatory is one of the three designated components of the Arctic Primary Station of the Network for the Detection of Stratospheric Change (NDSC). Among the complement of sensors being installed at Eureka are two state-of-the-art lidar systems for monitoring stratospheric ozone and polar stratospheric clouds (PSC). The ozone Differential Absorption Lidar (DIAL) system utilizes a xenon chloride excimer laser transmitter operating at 308 nm as the absorbed `on' radiation. A hydrogen Raman shifter generates the `off' wavelength at 353 nm. The system provides an average output power of about 60 watts at 300 Hz. The receiver is a 1 meter Newtonian telescope provided with several special optical features to permit daylight operation. The second lidar utilizes a Nd:YAG laser source operating at 1064 and 532 nm with a 20 Hz prf. This paper describes the new lidar facilities at AStrO and presents a summary of the data obtained during the first months of operation.
Aerosols are difficult to measure and model in the atmosphere because of their complex variability in space and time. Lidar systems offer excellent capabilities for studying atmospheric aerosols because of their ability to remotely monitor large volumes of the atmosphere from a single site with very high spatial and temporal resolution. This paper presents an overview of current lidar applications for aerosol measurements. The present status of such work is summarized and the advantages and limitations of lidar are discussed.