A Novel Absolute Salinity Sensor for Ocean Science

Oceanographers routinely deploy instruments to measure the temperature and conductivity of seawater and thereby compute its salinity and density. These measurements play important roles in a number of areas, some of which include ocean circulation and heat transport, climate science, and meteorology. The “CTD” technology in broadest use for measuring Practical Salinity has changed little in the last four decades, and it requires a geographical correction for conversion to the modern Absolute Salinity standard. Through recent work, we have developed a new profiling technology based on measuring the optical refractive index of seawater, a parameter that is more closely related to density than is conductivity. Our new technology is based on an innovative multi-wavelength interferometer that provides unprecedented resolution of seawater density and can profile with millimeter-scale spatial resolution. Accordingly, it can provide an alternative or complementary measurement to the standard CTD approach. Because of its close correspondence with density it also provides a method for determining the Absolute Salinity, recently recommended as an alternative to conductivity-based Practical Salinity. Here we give an overview of the technology and present performance data from initial laboratory calibrations and ocean profiles.