Applications of numerical models for rough surface scattering

This thesis provides new computational models for electromagnetic surface scattering which allow large one and two dimensional problems to be considered through the use of efficient numerical algorithms and parallel computing techniques. This is in contrast with previous numerical studies that have been limited to relatively small surfaces rough in one dimension only. The new numerically exact models are applied to several problems of current interest, and allow studies of phenomena not predicted by any available analytical theories. In addition, comparisons are made with predictions of standard analytical models to obtain an assessment of their performance. A one dimensional model for VHF propagation is the first numerical model considered. Comparisons with measurement data show the model to produce accurate results, and conclusively demonstrate the importance of terrain measurements in propagation predictions. Comparisons with approximate models allow their appropriate regions of validity to be determined. Polarimetric thermal emission from two dimensional periodic surfaces is studied using an extended boundary condition (EBC) numerical solution. The model is applied to generate the only numerically exact results for two dimensional surface polarimetric thermal emission currently available, and demonstrates that properties of UB, the third Stokes emission parameter, remain similar to those observed previously for one dimensional periodic surfaces. The response of UB to level of medium anisotropy is also investigated. A Monte Carlo study of backscattering enhancement from two dimensional perfectly conducting random rough surfaces follows, using a recently developed more efficient version of the method of moments which allows the large two dimensional surfaces investigated to be treated. Comparisons with bistatic scattering data from machine fabricated random surfaces taken at the University of Washington illustrate the first such validation of a two dimensional numerical scattering model to date. Backscattering enhancement is observed in both theoretical and experimental results, and theory and experiment are in good agreement. Scattering from the surface of the ocean is studied using a two dimensional perfectly conducting surface Monte Carlo simulation. A simple power law spectrum model is chosen for the ocean surface, and variations with spectrum low frequency cutoffs are illustrated in the simulation. Both forward and back scattering from the ocean are considered, and comparisons are made with the standard composite surface model of ocean scattering which indicate appropriate choices of the "cutoff' wavenumber in the composite model. The validated composite surface theory is then used with more realistic ocean surface models to compare with measured ocean backscattering data. Polarimetric thermal emission from the ocean is studied using a penetrable two dimensional surface Monte Carlo simulation. An extension to the standard penetrable surface method of moments is made to avoid greatly increasing the required number of surface unknowns for a highly lossy surface such as the ocean. Comparisons are made with the SPM and composite surface models for ocean scattering, and with available experimental data. Thesis Supervisor: Professor Jin Au Kong Professor of Electrical Engineering ACKNOWLEDGEMENTS I wish to express my sincerest thanks to Prof. J. A. Kong, my thesis supervisor, for his guidance on the studies of this thesis, and for his advice and insights into many other aspects of electromagnetics research. His excellence in teaching has enabled me to obtain the skills necessary for this work, and the research group he has created has provided an enriching environment in which to develop research skills. I also wish to express thanks to Dr. Robert T. Shin, for his unending enthusiasm for surface scattering studies, which has provided great motivation, and for his willingness to address all technical issues in a clear and thorough fashion, which has helped immensely in handling technical issues along the way. I am grateful for the access I have had to Dr. Shin's technical expertise and to his solid grounding in real world problems and expectations. Thanks also to Prof. F. R. Morgenthaler for serving as a thesis reader, area exam member, and TA advisor. I also wish to acknowledge collaborations with the University of Washington, particularly with Profs. Leung Tsang, Chi Chan, and Y. Kuga and with Kyung Pak. I appreciate the opportunity to have worked with Prof. Tsang while he was at MIT on sabbatical, and thank him for his willingness to collaborate in development and application of the SMFSIA approach. Collaborations with Groups 101 and 106 of Lincoln Laboratory are also acknowledged, with John Eidson of Group 106 providing a great deal of assistance with the propagation simulations of this thesis. In the EWT group at MIT, I would like to acknowledge all of the former members I have had the pleasure of interacting with, especially Drs. Ali Tassoudji, Murat Veysoglu, Simon Yueh, Son Nghiem, and Kevin Li. I would like to acknowledge the efforts of Dr. Eric Yang and Chih Chien Hsu in maintaining the group's computers, and the help of Kit Lai as the group's secretary. Many technical discussions with Dr. K. H. Ding are also appreciated. To all the current members of the EWT group, Chih Chien Hsu, Lifang Wang, Sean Shih, Yan Zhang, C. P. Yeang, Jerry Akerson, Fabio del Frate, and Nayon Tomsio, I wish you good luck in your continuing work and look forward to future collaborations. I appreciate the camaraderie we have shared, and acknowledge your help in many areas. Finally, I wish to thank my family for their continuing support through my graduate studies. This thesis is dedicated to my girlfriend Monica, who has shared every aspect of my life through the three years of this Ph.D. research with love, understanding, and thoughfulness. I look forward to our new future together. The support of ONR contract N00014-92-J-4098, NASA contract 958461, and a National Science Foundation graduate fellowship are acknowledged. Sponsorship was also provided by the U.S. Air Force, under contract no. F19628-95-C-0002. Use of the Maui High Performance Computing Center is acknowledged, sponsored by Phillips Laboratory, Air Force Material Command under cooperative agreement F29601-93-2001. The views and conclusions contained in this document are those of the author, and should not be interpreted as necessarily representing the official policies or endorsements, expressed or implied, of the US Air Force, Phillips Laboratory or the US Government.