Sound Speed

Definition  

Sound Velocity Profiling (SVP) of the water column is essential to the acquisition of swath mapping data, and is used for ray tracing through the water column. SVP influences directly the accuracy and uncertainty of both the horizontal and vertical position of each sounding and its impact is greatest towards the outer beams of the swath.  

Physical processes such as fresh water influx, solar warming of the upper water column, presence of mesoscale currents, and storm mixing can affect the temperature and salinity profile, and hence the SVP. These changes can occur at various spatial and temporal scales and can sometimes be observed in the water column backscatter data.  

Acquisition of SVPs must be planned to identify the relevant number and distribution of profiles and monitored carefully during the survey. 

If the sound speed at the transducer is different to the sound speed cast (by 2m/s for baseline surveys or 1m/s for the monitoring surveys) then another SVP should be collected.

The SVP can be acquired using direct SVP measuring device, XBT, bar check and CTD.

 Sound speed can be affected by: 

1. Temperature 

2. Pressure 

3. Salinity 

4. Depth 

Checks  

1. Check for “smiles” or “frowns” in the survey outer beams.

Pass Requirement

Sound speed check: Make sure that all the sound speed issues have been corrected in your bathymetry processing software (no “smiles” or “frown”) especially between adjacent survey swath lines. 

Examples

Example 1

Description   

202000013S Seamounts, Canyons and reefs of the Coral Sea. (GA-0365/FK200802) 

 Test results   

1. Sound Speed check: Sound speed issues discovered in the survey by GeoMapApp. 

Open

Figure: 1 Example of sound speed issues 

Open

Figure 2: The bathymetry profile plot for the swath line in figure:2 displaying the sound speed issue. 

Pass  

No 

Explanation   

This dataset does not meet the requirements outlined above as it fails check 1.