\prefacesection{Acknowledgments} 
Having finished writing and defending this thesis, I look back and realize that it would not have been possible in the short (by SEP's standards) period of almost four years without the valuable help of many friends and colleagues. They provided every sort of support to help me overcome the difficulty of getting back to academia after almost 20 years working for Petrobras. By the way, the first acknowledgment goes to this company, which  I call ``mine."  Thanks for the essential and continuous financial and moral support, the latter personified as Neiva Zago and Carlos Cunha.
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I thank Biondo Biondi, my adviser, for always being a source of encouragement and a reference on academic honesty. His attitude made clearer to me both the importance of obtaining good results and the usefulness of the bad ones, which deserve to be brought to light. I thank Jon Claerbout for initiating us students into the mysteries of  inverse problems and for sharing his contagious enthusiasm for doing research. I admire his energy, curiosity, and serendipity. Bob Clapp has constantly been steps ahead of everyone in looking for computational solutions that best fit the type and size of geophysical problems we propose to solve. Also, his knowledge about velocity inversion was of great help. Diane Lau, thanks for taking care of everything that makes SEP runs smoothly.
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I am indebted with all SEP colleagues with whom I overlapped and shared ideas, coffee, and beer. Daniel Rosales, Gabriel Alvarez, Brad Artman, Alejandro Valenciano, Bill Curry, Guojian Shan, Jeff Shragge, Yaxun Tang, Madhav Vyas, Ben Witten, and Pierre Jouselin, arrived at SEP before me. Their hospitality and interest in teaching me the way SEP works will be remembered forever. Special thanks to Alejandro Valenciano and Yaxun Tang with whom I shared the office and who tutored me on several aspects of seismic inversion using wavefields. Roland Gunther, Gboyega Ayeni, and I started SEP in the same year. Otunba Ayeni \`{i}d\'{u}p\"{e}\^{o}p\"{e} f\'{u}nn\'{i}tor\'{i} gbogbo \~{o}kan. Xukai Shen, Adam Halpert, Sjoerd de Ridder, Abdullah Al Theyab, Mohammad Maysami, Yunyue Li, Mandy Wong, Nader Moussa, Ohad Barak, Ali Almomin, Yang Zhang, Chris Leader and Kittinat Taweesintananon, started SEP after me. Thanks for lending me your energy during the final sprint to finish up everything. System administrators deserve a special thank for configuring and maintaining our computers: Bill, Yaxun, and Ohad. I cannot forget the reproducibility guys: Ben, Jeff, Mohammad, Sjoerd, and Yang.
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Two people were crucial to improve readability of this thesis: Dawn Burges and Professor Claude Reichards. Besides the editorial job, Claude will be remembered by his friendship and support.
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Lais, Tomas, Mateus e Gabriel, muito obrigado pela compreens\~{a}o e amor que pautaram nossas vidas nesses quatro anos. O que fiz foi para voc\^{e}s. Merecemos todo o bem que vier. A voc\^{e}s todo o meu amor e gratid\~{a}o.

