The Salinity Processes in the Upper Ocean Regional Study (SPURS) is a series of science missions focused on understanding how surface salinity variations affect ocean circulation. While primarily a physical oceanography initiative, hydrographers reference SPURS data and methodologies when modeling regional sound speed profiles. Understanding upper-ocean salinity dynamics is critical for correcting acoustic refraction in deep-water multibeam surveys.
Check the historical salinity data from the SPURS project to see if we should expect a strong halocline in this survey block.
Salinity has a much smaller effect on sound speed than temperature or pressure, but in areas with massive freshwater runoff or high evaporation, ignoring it will introduce refraction errors in the outer beams.
Related terms
SVP
Sound velocity profile: how the speed of sound changes with depth through the water, measured to correct sonar depths.
Surface sound speed
The speed of sound right at the sonar face, measured continuously so the multibeam can steer its beams.
Refraction
The bending of sonar beams as they cross water layers with different sound speeds, which distorts depths if uncorrected.
Cast
One lowering of a sound speed or CTD probe through the water column to measure a profile.