A Hierarchy of Models for Lidar Multiple Scattering and Its Applications for Simulation and Analysis of Spaceborne Lidar Returns

摘要

In lidar remote sensing the classical lidar equation is normally used for the retrieval of environmental parameters from the return signal. One of the most important reasons for this is the simplicity of this equation which describes the contribution of single scattering to the return signal only. But it is well known that multiple scattering occurs in lidar sensing of dense clouds and remote cirrus clouds. Therefore a more and more precise description of lidar returns is needed. We present a stochastic model for the description of the transport of light through the atmosphere and obtain an exact multiple scattering lidar equation from which by introducing simplifying assumptions step by step the classical lidar equation may be derived. Of course, more information about the scattering behaviour of the scattering particles or molecules of the atmosphere is needed for such an exact multiple scattering equation, but the more input is necessary the more output is possible. Indeed, it is possible to obtain simultaneously quite different environmental parameters (e.g. extinction and size distribution) from one multiply scattered return signal. We show examples of simulations of returns of a ground-based and a spaceborne lidar from water clouds, cirrus, and haze. These simulations and the obtained importance of the contributions of higher orders of scattering show the need for a more precise modeling of lidar returns, especially for spaceborn lidars.