Temporal variation of sound speed in ocean: A comparison between GPS/acoustic and in situ measurements

Motoyuki Kido, Yukihito Osada, Hiromi Fujimoto

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)


The GPS/acoustic technique applied to seafloor geodesy intrinsically measures integrated sound speed along a trajectory of an acoustic signal as well as the position of a seafloor transponder array. We present here a generalized expression of sound speed variation in terms of a traveltime residual normalized to the vertical component. With this expression, residual traveltimes to any seafloor transponders will have a same value regardless of their depths and slant angles. This is valid even for the case having horizontal gradient in sound speed structure; the gradient affects only on positioning of a transponder array and not on the estimate of sound speed just beneath the observation point. We monitored temporal variation of this quantity through a GPS/acoustic survey and compared it with in situ expendable bathythermograph (XBT) measurements periodically carried out during the survey. We found that the relative change of the two independent measurements are in good agreement within 5% of the typical amplitude of temporal variation.

Original languageEnglish
Pages (from-to)229-234
Number of pages6
JournalEarth, Planets and Space
Issue number3
Publication statusPublished - 2008


  • GPS/acoustic technique
  • Seafloor geodesy
  • Sound speed
  • XBT


Dive into the research topics of 'Temporal variation of sound speed in ocean: A comparison between GPS/acoustic and in situ measurements'. Together they form a unique fingerprint.

Cite this