Monte Carlo Simulation of Radiative Transfer in Atmospheric Environments for Problems Arising from Remote Sensing Measurements

Abstract

The way in which solar radiation distributes itself in the atmosphere and on the ground is well known. It is beyond the scope of this book and the reader can refer to more specific references (Kondratyev, 1969; Goody & Yung, 1995; Liou, 1998) for more detail. Solar radiation, essentially in the visible-ultraviolet frequency range, and infrared radiation, emitted by the terrestrial surface, are the prevailing energy sources for general atmospheric circulation. They are thus particularly important for meteorological and climatic studies. It would therefore be of great interest, for instance, to be able to calculate the influence of the presence of ozone and trace gases, water vapour and clouds, and various aerosols on radiative transfer and global thermal energy in the atmosphere or in particular regions of it. These considerations naturally lead to the analysis of radiative transfer in the terrestrial atmosphere. This can be done using an atmospheric radiative transfer model (RTM) which also includes the possibility of single and multiple scattering events. Numerical and analytical methods can be used to solve a radiative transfer equation (Stamnes et al., 1988; Lenoble, 1977; Fouquart et al., 1980). A Monte Carlo approach is particularly suitable when multiple scattering significantly affects the results or where marked anisotropy of scattering and complex geometrical configurations are involved. The interest in such problems has increased through recently developed techniques related to remote sensing observations (satellite-based, ground-based or airborne) of the Earth's surface and atmosphere, involving the use of spectral radiation dispersion systems (mainly radiometers, spectrometers and interferometers) and active systems (principally RADAR, LIDAR and SODAR) Among these various techniques, DOAS (Differential Optical Absorption Spectroscopy) and LIDAR (Light Detection And Ranging) investigations on the presence of particular atmospheric constituents or of atmospheric phenomena such as clouds, fog, rain, etc., are of special interest. With reference to surface remote sensing observations, for instance, the effects of atmospheric absorption and scattering constitute a noise element, which has to be evaluated by calculations. Simulation of both LIDAR and DOAS systems deals with radiation in the UV/visible spectral range. For simulation purposes, a LIDAR system can be schematized as a pulsed