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Surveying

Water Column Profiles - Conductivity Temperature Depth (CTD) & Sound Velocity (SVP)

Density variations in the water column due to changes in the salinity, temperature and/or pressure result in a deviation in the path of the sound wave from the sonar equipment used to survey. As a consequence, soundings of depth will have an error.

To ameliorate the problem, an instrument called a CTD or SVP is lowered through the water column measuring salinity, temperature and depth at regular intervals. This data is used to generate a profile which is entered into the MBES equipment that subsequently corrects the data for the effects of changes in water properties with depth. The smaller Sound Velocity Probe (SVP) is used to directly measure the sound speed where space on the vessel is restricted.

Images of the CTD being lowered from the RV Celtic Explorer off the coast of Kerry (top) and the instrument is held just below the sea surface to allow it to acclimatise before lowering through the water column (bottom).

Vessels | Acquisition | Tides | Referencing | Sound Velocity | Ground Truthing | Survey Progress

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