1 oc679 acoustical oceanography acoustic tomography – multiple source/receiver pairs uses...
TRANSCRIPT
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
6Oc679 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