Simulation of coherent Doppler LIDAR signals and their analysis with the Cohen's class : application to algorithms design for wake vortex detection and characterization

Abstract

The problem of wind statistics measurements in the planetary boundary layer using a coherent Doppler LIDAR is addressed. More specifically, it focuses on the design of efficient algorithms in the time-frequency space dedicated to the detection and the characterization of atmospheric hazards, such as aircraft wake vortices or wind shears. To support this study, a simulation program has been developed which combines the numerical simulation of LASER beam propagation in a turbulent medium with state-of-the-art Large Eddy Simulation (LES) of wake vortex in atmospheric turbulence or in ground effect. This tool constitutes a complete framework for optimizing the LASER source while developing and evaluating the performance of the whole estimation process. Moreover, an analytical formulation of the coherent LIDAR Wigner-Ville spectrum has been derived along with its associated Cohen’s class of time-frequency estimators. This theoretical basis leads to explicit equations of the wind statistics that are actually retrievable, depending on the measurement conditions and the laser pulse parameters. It also yields to an adaptive spectral modeling algorithm which is used to detect the wake vortices and then estimate their wind speed probability density function as well as their extremum radial velocity profiles, related to the vortex maximum tangential velocity. Another major achievement of this thesis is the development and the validation of a fast inversion method dedicated to wake vortex characterization, e.g. the estimation of its position and intensity. In this method, a Burnham-Hallock model, transformed by a new measurement model integrating the effects of the estimation process, is directly matched to the retrieved radial velocity map. Monte Carlo simulations have been carried out on both analytical models and LES to confirm its good performance. Finally, the validation of the axial detection of vortices with a fiber-based LIDAR has been performed during a test campaign conducted by ONERA at Orly airport in April 2008 during the FIDELIO project. Wake vortex signatures have been successfully obtained with some of the algorithms developed in this thesis.(FSA 3) -- UCL, 201