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 edited on the Graph tab or the Table tab:

Graph tab:

• 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

Table tab:

• Edit depth and sound speed values directly in the table
• Use the + and - buttons to add or remove points

Data can also be pasted from the clipboard (two columns: depth, speed) using the Paste button.

The profile is linearly interpolated between control points.

Custom SSPs can be saved to and loaded from the user database using the dropdown and save/remove buttons.

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.

Current and Tide

A constant ocean current speed and direction may be entered. The direction can be set by clicking directly on the compass rose.

A tidal offset can be applied to raise or lower the water level relative to the bathymetry.

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.

The absorption calculation method can be selected explicitly: Fisher & Simmons (1977) or Ainslie & McColm (1998). The absorption curve is shown on the graph tab and can be exported as CSV using the Save attenuation as CSV button.

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.