Water salinity detection using a smartphone

Abstract This paper demonstrates the operation of a smartphone based platform salinity sensor for accurate and reliable monitoring of salinity level in oceanic water environment. To measure water salinity level using the smartphone, two different approaches have been proposed and their sensing performances have been compared. The first approach is based on Beer-Lambert principle where collimated light beam from an optical source while passing through the medium gets attenuated due to absorption by the medium which can be detected and analyzed by the smartphone. The second approach is based on evanescent field absorption from an uncladed U-bent sensing region of an optical fiber. Variation in salinity level of the surrounding medium of the fiber sensing region affects the absorption of evanescent field and this can be monitored by the smartphone. Two freely available android applications have been used for detection and analysis of salinity level. The designed smartphone sensor has an ability to measure salinity level variation as low as 0.1 parts per thousand (ppt) with high accuracy and repeatability. We envision that owing to its compact size, low-cost and truly user-friendly in nature, the sensing techniques could emerge as potential alternative to existing salinity sensors that would be useful for different in-field applications.