Raman Lidar Signal Filtering in Water Vapor Remote Sensing

A Raman lidar (Light Detection And Ranging) can be implemented in the straightforward fashion illustrated in Fig. 1. The system operates by transmitting a laser pulse of arbitrary wavelength λ0 and recording radiation backscattered from the atmosphere as function of time to provide range information in a similar manner to a radar system. The return signal contains a strong elastically scattered component (at λ0) that is useful for profiling clouds and aerosols and also weaker inelastically scattered components that provide chemical-specific information. For profiling water vapor, we use components produced by vibrational Raman effect that produces energy shifts characteristic of the molecules in the atmosphere (3652 cm-1 for water vapor, 2331 cm-1 for nitrogen). The aim of this paper is to process lidar backscattered signal that contains water vapor and aerosol information in order to improve their recovery. Since they are affected by different kinds of noise, an appropriate filtering, with an improved recovery, represents a way to get good estimates of the above components.