The idea for acoustic tomography arose abruptly. Because we can mark a clear conceptual start, the following brief chronicle of the development of ocean acoustic tomography, given from our perspective as participants, may be of interest.

Some hopes for “Monitoring the oceans acoustically” were voiced at the thirtieth anniversary of the founding of the Office of Naval Research (ONR) (Munk and Worcester, 1976). A “Preliminary report on ocean acoustic monitoring” was prepared during the JASON Summer Study (JSN-77-8) by Garwin, Munk, and Wunsch. That work was expanded into “Ocean acoustic tomography: a scheme for large scale monitoring” (Munk and Wunsch, 1979), which examined the acoustic and inverse theoretical requirements for mapping the oceans with mesoscale resolution. It concluded that “an acoustic tomographic system appears to be both practical and useful.” The name “ocean acoustic tomography” was deliberately chosen to arouse the reader's curiosity as to what it is all about. Response by the oceanographic community was varied; those with a background in inverse theory regarded the inverse problem as trivial, but found the acoustic applications to be of interest, whereas the marine acousticians were interested in the inverse problem.

Overture

Advances in several fields were prerequisites for the development of ocean acoustic tomography: an understanding of underwater sound propagation, a statistical description of oceanic processes (especially internal waves and other fine structure), and the availability of inverse methods for inference from measurements. In this section we focus on the history of the acoustic developments crucial to tomography.