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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 (farthest sounding).  

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 sound speed at transducer varies by 2m/s for baseline surveys (or 1m/s for monitoring surveys) another SVP should be collected. Otherwise, the outer beams of the swath shows a “smile” or a “frown” for under corrected or over corrected sound speed.  

The SVP can be determined using one of the following methods:  

  1. direct observation via deployment of an SVP measuring device  

  2. calculation of the SVP through deployment of an expendable bathy thermograph (XBT)  

  3. bar check  

  4. calculation of the SVP using CTD (Conductivity/Temperature/Depth) data and applying the UNESCO formula  

 

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. Correct the sound speed issues in your bathymetry processing software.

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. 

 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. 

Pass  

No 

Explanation   

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

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