1. 1 Oc679 Acoustical Oceanography Acoustic Tomography – multiple source/receiver pairs uses differences in speed along multiple paths to deduce the structure of the medium between source and receiver the measurement is of the times of pulse arrivals numbered peaks indicate total number of ray turning points along ray path between source and receiver (up & down) this example shows the difficulty in making an unambiguous determination of a particular signal note here that the +20 ray traveled closest to the channel axis (at slower speed) and thus arrived last – it was also attenuated the least analogy to medical X-ray scanning procedure (CAT for computer-assisted tomography) tomography – imaging by sections / xray / optics / acoustics …

2. 2 Oc679 Acoustical Oceanography Ocean Tomography Group - Nature 1982 primary technical problems: mooring position keeping time keeping sources – 1’ diameter tubes driven at closed end by piezoelectric ceramic at 224 Hz

3. 3 Oc679 Acoustical Oceanography Ocean Tomography Group - Nature 1982

4. 4 Oc679 Acoustical Oceanography Ocean Tomography Group - Nature 1982

5. 5 Oc679 Acoustical Oceanography Ocean Tomography Group - Nature 1982

6. 6 Oc679 Acoustical Oceanography Ocean Tomography Group - Nature 1982 observation from a remote receiver 2000 km north of array includes systematic fluctuations in travel time travel time shortened by 0.8 s at mid-record due to 200 km northward displacement of GS and associated decrease in cold slope water along path