Acknowledgments

I thank Biondo Biondi for guidance and to Paul Sava for meaningful discussions. I thank Guojian Shan for the pseudospectral wave propagation code used in Figure . I thank Dr. Ralph Shuey of Gulf Science and Technology Company for making the Grand Isle dataset used in Figure available to SEP (1978). I thank ChevronTexaco for providing the synthetic velocity model used for Figures and and the dataset in Figure .