1 Oc679 Acoustical Oceanography Acoustic Tomography – multiple source/receiver pairs uses differences in speed along multiple paths to deduce the structure.

1Oc679 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 receiverthe 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 …

2Oc679 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

3Oc679 Acoustical OceanographyOcean 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

1 Oc679 Acoustical Oceanography Acoustic Tomography – multiple source/receiver pairs uses differences in speed along multiple paths to deduce the structure.

Documents

travel time travel time

time keepingsources

ray path

total number of ray

multiple paths

remote receiver

slower speed

tomographytomography