Sound travels through water at approximately 1500 m per second. However, slight variations in the salinity, temperature, pressure and turbidity of the water column combine to deflect the sound wave as it travels to/from the sensor. This results in sounding errors unless corrected for. Therefore, knowledge of ambient sound speed conditions at each location is critical to an accurate survey.
To solve this problem an instrument measuring Conductivity, Temperature and Depth (CTD) is lowered to the seabed in each survey area. This generates a profile of the water column which is used to calibrate the acoustic instruments such as the Multibeam Echosounder. Sound velocity at the sea surface is also measured.
Controlling these parameters can be quite a challenge in complex oceanographic conditions. For example, in a shallow bay with a freshwater influence (like a river) the speed of sound through water is highly variable. The water column is generally more stable as we move away from the coast where there is less mixing of salt and freshwater. During surveys multiple daily Sound Velocity Profiles (SVPs) with state-of-the-art sensors are taken to ensure INFOMAR survey data is of the highest possible quality in each area.
Read more about how changing oceanographic conditions are considered during survey aquisition using the blue buttons provided.