We are grateful to the reviewer (Peter Huybers) for his critical review and for many positive recommendations. We thank Chris Garrett, Rob Pinkel, and Harper Simmons for having put us straight on many issues; so has Carl Wunsch, unaware that he was to be the victim of this missile.
One of us (WM) was the recipient of a 65th birthday celebration on 19 October 1982, organized by Chris and Carl. On that morning, I telephoned Carl at the Massachusetts Institute of Technology (MIT) for advice on some manuscript, unaware that he had spent the night in our basement guest room. Carl’s secretary professed ignorance of his whereabouts, and when I called Marjory she said, “Carl does not always tell me where he is going.”
Carl’s contribution to the birthday volume was Acoustic Tomography and Other Answers (Wunsch 1984). The “other answers” in this title refer to “9-W” and two other answers from which one was to infer the question by “inverse theory” (IT). Carl had recently embarked on his lifelong obsession with IT. If you cannot infer the question corresponding to “9-W,” you can blame it on a defect of IT.
The other part of the title, acoustic tomography, refers to our joint efforts to rely on the intrinsic properties of ocean acoustics for monitoring ocean variability, and was to result in eight joint papers and a book. At one time we thought that the combined application of satellite altimetry (Carl’s major contribution to ocean observation) and acoustic tomography would become the cornerstones for large-scale ocean monitoring, but this has not been the case, not yet.
We have shared so many interests since Carl, then a Stommel graduate student, first showed up at my doorstep in 1966 to have a look at tides. We both have had three sabbaticals at the University of Cambridge, the last jointly in 1981–82, and 40 years of friendship. Walter Munk holds the Secretary of the Navy Chair in Oceanography.
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