working with Doug Webb, also at Woods Hole, transformed the latter's successful SOFAR floats into moored sources transmitting CW and m-sequences. In 1978, the Munk and Worcester group from Scripps, and the Spindel group from Woods Hole, sailed together on a research cruise aboard the Scripps vessel R/V Thomas Thompson. They had been encouraged to work with each other by Hugo Bezdek, the program manager for their common sponsor, the U.S. Navy Office of Naval Research, because he realized their interests were complementary. Worcester deployed his instruments in an acoustic navigation net installed by Spindel, and Spindel conducted the first test of an autonomous source emitting m-sequences.
Meanwhile, Walter Munk, together with Carl Wunsch at MIT, was also working on the oceanographic problem of understanding and observing the newly discovered mesoscale. Munk, who had worked on acoustics with the DARPA group, and Wunsch, who had pioneered the application of inverse methods to oceanography, brought together just the right combination of interests and background to spawn the new concept of ocean acoustic tomography(22). The idea provided the quantitative basis for acoustical ocean observation and monitoring that until then had been lacking.
Figure 7. Worcester (center) and Spindel (right) on an early tomography cruise. Paul Boutin, between them, and John Kemp, at left were responsible for mooring design and deployment. They are examining a component of one of the first tomographv receivers which was based on a CMOS microprocessor with 8K of RAM and 4K of ROM, and contained a Rb frequency standard that monitored a less stable, but more power conservative clock (23). Modern receiver versions are based on its architecture.
The team that pioneered the development and implementation of tomography grew out of these efforts ― the Munk and Wunsch collaboration, Worcester's reciprocal transmissions, Spindel's portable range, and the joint Scripps-Woods Hole cruise. It led to the first tomography experiment in 1981, and as it is said, “The rest is history.”
The Present
Twenty years have passed since that 1978 cruise and the publication of Munk and Wunsch's seminal paper on acoustic tomography. In that time the field has developed to where ocean acoustic tomography research is conducted world-wide. There are active experimental groups in the U.S., in France, Germany, Portugal, and Greece in Europe, in Russia, in South Korea in China, and in Japan.
