Electromagnetic Wave Scattering by Randomly Buried Particles

In this thesis, the effect of volume scattering from the buried particles in half-space random media on the radar backscattering cross section is investigated. The radar clutter from a flat desert area is modeled as spherical scatterers randomly embedded within a layered medium with flat interfaces. Three approaches are used to calculate the backscattering coefficients. The Monte Carlo method based on Transition matrix (T-matrix) approach is first applied. The multiple scattering and the coherent wave interaction are included in this approach. The couplings between scatterers and the interface are taken into account by using the image method. The multiple scattering equation is solved using the iterative technique. The solution process repeated for many realizations and averaged to calculate the backscatter. The Radiative Transfer theory (RT) approach is also presented. The RT theory is based on the concept of energy transport and the assumption of independent scattering. The numerical solution of the RT equation is obtained using the discrete-ordinate eigenanalysis method, which includes all orders of multiple scattering. Finally, the First Order Analytical Approximation is applied to obtain the first order solution of the multiple scattering equations derived based on T-matrix method. The First Order Analytical Approximation assumes positions of particles to be independent. The effects of coherent wave interactions are considered in this approach. However, the multiple scattering effects are neglected. The Rayleigh scatterer is assumed for each particle. A compact analytic expression for the backscattering coefficients is obtained. The numerical calculations from all three approaches are performed and then compared. It shows that the results using RT approach are in good agreement with those of the Monte Carlo approach in this study. The First Order Analytical Approximation always gives higher returns than the other two methods, which may be accounted for by the assumption of independent particle position. Thus, from this study, though not including coherent wave interaction, the RT approach is a good model in prediction the radar return from desert media. Some parametric studies base on RT are also performed which shows that the particle size plays an important factor in the high radar return level. Thesis Supervisor: Jin Au Kong Title: Professor Thesis Supervisor: Kung Hau Ding Title: Postdoctoral Associate Acknowledgments I first of all wish to sincerely thank Prof. Kong for giving me the opportunity to be a member in this superb research group and for his excellent teaching which inspired me a lot of insightful knowledges in this electromagnetic area. Thanks to Dr. Shin for his ingenious guidance throughout the work, which made this work much simpler. Thanks to Dr. Lee for his advise, guidance, sparkling ideas, not only in the technical subjects but also aspects of ways to live a happy life, and for his explanations to all of my stupid questions, ever since I was wondering why the Green's function was not a red or blue function until now I know the Green's function better than my student ID., and for his patience to all the mistakes I have done throughout. I am especially indebted to Dr. Ding for his help, particularly the early period of my studying, and for his kindness to my ignorance. Without his numerous explanations, comments, suggestions, corrections and hints, I wouldn't have made it this far. I gratefully recognize all of my colleagues in the group. Thanks to Chih, Sean for answering me all those questions. Thanks to C.P., Gung, Lifang, and Kevin. Thanks to Joel for his friendliness. I really had fun at the Halloween party that night. Thanks to Jerry, especially for going with me to my driver's license road test. Thanks to Yan, who always brought many interesting discussions to me, though I couldn't answer everything. Also thanks to Kent, a good driver who drove us to all the parties and picnics. Special thanks and sincere best wish to Christina, a lively, nice and very talkative woman and one of the best friends of mine. Thanks to Ping (if it were not for you this thesis would have been finished long before, just kidding!) for those hard times and happy times we were and will be together. Finally, I would like to express my gratitude to my parents whose love never failed to give me the energy to survive this very tough year at MIT. The merit of this thesis, should there be any, is dedicated to them.