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Water

Speed of sound profile

The vertical sound speed profile is set on this page. Some default profiles may be selected from the dropdown menu. Note that if a profile is listed as 'normalised' then the given profile will be scaled so as to extend from the water surface to the greatest depth in the current model. Profiles that are not normalised will use the depths stored with the profile.

The current profile may be modified:

  • Double click on the graph to add a new control point
  • Double click on an existing control point to remove it
  • Click and drag to move existing control points

The profile is linearly interpolated between control points.

If you create a new point at a higher or lower speed than any existing points, it may seem like the point is created at the wrong position - this is because the graph x axis rescales if necessary when new points are added.

Ocean current

A constant ocean current may be entered in the field. The direction may be entered by clicking directly on the compass rose.

Water properties

The water temperature and salinity may be entered in the appropriate fields. Preset properties may be selected from the dropdown box. The graph shows the water absorption with frequency, in units of dB/km.

For standard ocean conditions (salinity 35 ppt & pH 8) dBSea uses (Fisher & Simmons, 1977) to calculate absorption. If other values are chosen the method described in (Ainslie & McColm, 1998) is used.

Please keep in mind that the above models have best accuracy within certain limits:

Fisher & Simmons:

  • Temperature: -2°C to 22°C
  • Salinity: 35 ppt
  • Depth: 0 to 3500 metres
  • pH: 8

Ainslie & McColm:

  • Temperature: -6°C to 35°C
  • Salinity: 5 to 50 ppt
  • Depth: 0 to 7000 metres
  • pH: 7.7 to 8.3

References

  1. Ainslie, M. A., & McColm, J. G. (1998). A simplified formula for viscous and chemical absorption in sea water. Journal of the Acoustical Society of America, 103(3), 1671-1672.

  2. Fisher, F. H., & Simmons, V. P. (1977). Sound absorption in seawater. Journal of the Acoustical Society of America, 62, 558-564.