Acoustic remote sensing of ocean flows

Abstract

Acoustic techniques have become powerful tools for measurement of ocean circulation mainly because of the ability of acoustic signals to travel long distances in water, and the inherently non-invasive nature of measurement. The satellite remote sensint techniques employing active and passive optical thermal and microwave signals, and coastally operated remote seusing techniques employing active electromagnetic signals in the H.F. and microwave bands are unable to penetrate below a very thin surface layer of the ocean surface and hence these techniques are unusable for measurement of subsurface circulation. The three methods of ocean circulation measurement using acoustic remote sensing techniques are the Lagrangian, Eulerian and single-profiling. Acoustic techniques used in oceanography for Lagrangian measurement of sub-surface flows are: 1) Tracking of sub-surface floats by ship-borne hydrophones, 2) Tracking of SOFAR floats, 3) Tomography, 4) Reciprocal transmission, 5) Sapce-time scintillation analysis. These five techniques are briefly discussed.