146 IEEE SENSORS JOURNAL, VOL. 15, NO. 1, JANUARY 2015 A Portable Optical Sensor for Sea Quality Monitoring Filippo Attivissimo, Member, IEEE, Carlo Guarnieri Calò Carducci, Anna Maria Lucia Lanzolla, Member, IEEE, Alessandro Massaro, Member, IEEE, and Maria Rosaria Vadrucci Abstract—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. Index Terms— Optical sensing, lock in, fluorescence, sea water monitoring, chlorophyll. I. I NTRODUCTION F OR thousands of years the sea has been an important resource for the livelihood and well-being of European populations, but the possibility of exploiting this resource is increasingly threatened by degradation, mainly due to the pressure of human activities, as attested in international direc- tives [1], [2]. In this context growing attention has been paid to monitor air and water pollution for reducing health risk and preserving the ecosystem [3]–[5]. In recent years, the increasing of both manufacturing indus- tries and coastal tourism has exposed the Mediterranean Sea to great environmental pressures. On the other hand, the discharge of industrial and municipal wastewater can be considered a constant polluting source and a potential cause of alteration for the Mediterranean Sea [6], [7]. Eutrophication has been considered one of the major threats to the quality of marine ecosystems including Mediterranean. Manuscript received March 27, 2014; revised July 3, 2014; accepted July 3, 2014. Date of publication July 16, 2014; date of current version November 5, 2014. The associate editor coordinating the review of this paper and approving it for publication was Dr. Anna G. Mignani. F. Attivissimo, C. G. C. Carducci, and A. M. L. Lanzolla are with the Department of Electric and Information Engineering, Polytechnic of Bari, Bari 70125, Italy (e-mail: attivissimo@misure.poliba.it; carlo.guarnieri@libero.it: lanzolla@misure.poliba.it). A. Massaro is with the Center for Bio-Molecular Nanotechnologies, IIT Lecce, Lecce 73010, Italy (e-mail: alessandro.massaro@iit.it). M. R. Vadrucci is with the Regional Environmental Protection Agency, Lecce 73100, Italy (e-mail: m.vadrucci@arpa.puglia.it). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2014.2340437 It can be defined as “an increase in the rate of supply of biomass and organic matter” [8], mainly due to nutrient enrichment that stimulates the primary productivity of pelagic compartment (phytoplankton), of benthic micro and macro algae and high plants. The eutrophication reduction is a primary objective in both Water Framework Directive (WFD-2000/60/EC) [8] and in EU Marine Strategy Framework Directive (MSFD-2008/56/EC) [8]. Chlorophyll-a is considered as a proxy for indirect biomass measurements in pelagic ecosystems. Chlorophyll-a is a pigment involved in photosynthetic processes to produce carbohydrates and life-sustaining oxygen, starting from water, carbon dioxide and sun light. It is present in phytoplankton, macroalgae and other water plants. It absorbs most energy from wavelengths of violet-blue and orange-red light. The primary effects of eutrophication are excessive growth of phytoplankton, increasing concentration of chlorophyll-a , increasing of the amount of organic matter settling on the bottom and reduction of water transparency [10]. As a consequence, chlorophyll-a and water transparency represent important parameters for the assessment of the quality status of marine ecosystems [11] and therefore they are included in most eutrophication monitoring programs. For this reason, Chl-a values have the best geographical coverage at the European level [12]. In marine ecosystems, chlorophyll-a concentration shows an intrinsic natural variability as on temporal scale, as on spatial local scale (inshore-offshore) and on biogeographic scale. In Mediterranean sea the average values vary between 0.2-1.5 μg/l [12] except in proximity of rivers delta or estuaries, as in the case of Po river in the Northern Adriatic sea where the increase of nutrients input promotes algae replication rising the inner chlorophyll-a concentration up to 8 μg/l [13]. The “in situ” quantification of chlorophyll a is based on fluorimetric methods, using optical probes that measure arti- ficially induced phytoplankton fluorescence. Optical detection could be a good solution being the elements (photosynthetic organisms and organic and inorganic particles) to be monitored of micro-scale dimensions. Concerning large scale problems, optical probes were previously studied for other types of sea water pollution such as oil spill [14]. Often the variation of trophic status is not a visible feature as in oil spill, because it is in the chemical processes supported by micro-elements contained in the water. Hence a way to optically evaluate this 1530-437X © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.