Refractometer resolution limits for measuring seawater refractive index

Measurement of seawater salinity, with a high accuracy, has become a key issue in thermodynamic ocean control. One of the most direct ways is to measure the seawater refractive index, which can then be related to the salinity. Refractometry is the most direct and simplest way to measure refractive index. Recent advances in high resolution position sensitive devices (PSDs) compel us to consider the physical limits and resolution of beam deviation measurement methods, such as refractometers, when additional constraints such as compactness are imposed. This work proposes to assess what can be achieved with such technology with respect to the current technical state of the art. In particular, we present the resolution dependence to refractive index variations, and derive the limits of such a solution for designing seawater sensors based both for coastal and deep sea applications