A portable optical sensor for sea quality monitoring

In this paper, we propose the modeling, the design, and the development of a high sensitivity cheap optical sensor for chlorophyll a and water transparency based on chlorophyll fluorescence and turbidity due to scattering for in situ monitoring of trophic status of seawater. The sensor is designed in order to detect very low chlorophyll concentration and low level turbidity by means of a numeric lock-in amplifier technique, with a common resonant input stage. The sensor is designed and implemented by considering a proper layout suitable for a good light source coupling. The presented prototype integrates on a board two LED sources emitting red and blue light to measure both chlorophyll-a and turbidity. The system assures a chlorophyll sensitivity of 1 mV/2.5 μg/l, a detectivity of 0.2 μg/l, with a 40-dB minimum attenuation of all the other light sources. It is attractive with respect to commercial systems because it guarantees considerable reliability with low manufacturing costs.