Accession Number:

ADA181690

Title:

Global Model for Sound Absorption in Sea Water. Part 3. Arctic Regions

Descriptive Note:

Technical rept.

Corporate Author:

NAVAL UNDERWATER SYSTEMS CENTER NEW LONDON CT

Report Date:

1987-05-14

Pagination or Media Count:

42.0

Abstract:

Sound absorption in sea water is known to be caused by ionic relaxations involving magnesium sulfate, boric acid and magnesium carbonate. Absorption is regionally dependent, due mainly to the pH-dependence of the boric acid relaxation. In the nominal sea-water pH range 7.7-8.3, the magnitude increases by roughly a factor of four at the lower frequencies. Since pH varies with depth as well as location, absorption also depends on the ray paths. A predictive global model for the World Ocean has developed, employing contour charts of the pH correction-factor K-factor at the depths, 0, 0.5, 1, 2, and 4 km. Profiles required for loss-integration along ray paths can be generate by the algorithm provided. This report extends the model to cover Arctic regions. In polar waters, sound speed generally increases monotonically with depth and upward refraction causes a concentration of energy near the surface. Excess attenuation, evidently due to underice scattering, makes long-range propagation feasible only at very low frequencies. Reverberation is also an order of magnitude higher than that at lower latitudes. Thus absorption effects are important only for direct-paths and high frequencies. For depths of 1 km or less, the ranges of concern are therefore on greater than about 50 km in ice- covered waters. The range of pH in the Arctic Ocean is roughly 8.0-8.3, corresponding to an absorption range of a factors of two at most. Because the variability occurs much closer to the surface, the depths 0, 0.1, 0.3, 0.5 and 1 km are found only in basin regions and variability is negligible at these depths.

Subject Categories:

  • Physical and Dynamic Oceanography
  • Acoustics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE