Publication: In situ salinity measurements in seawater with a fibre-optic probe
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IOP Publishing Ltd.
We have successfully proved the feasibility of an optical salinity meter for marine applications in a two-week measurement campaign, carried out for the realization of in situ salinity measurements in seawater. An optical instrument (optode), in which the main element is a fibre-optic refractive-index sensor based on surface plasmon resonance (SPR), has been developed for that purpose, and has been especially designed to be able to operate in realistic conditions. The performance of the optode has been evaluated on an oceanographic ship in the Baltic Sea, close to the Vistula estuarine area. The obtained results (in different tests, such as depth-profiling, towing and stationary measurements) show good correlation with the data provided by a commercial probe. Although the device is currently a part of a more complex measuring platform and uses an axial spectrograph as detector, the output power measurement used and the simplicity of its conception allow us to conceive a closed, extremely compact set-up which can be in principle commercially competitive with existing sensors.
© 2006 IOP Publishing Ltd. This work has been partially supported by European Project MISPEC, contract number EVK3-CT2000-00519, Spanish Project OPTIMA, Programa Nacional de Recursos Naturales, MCYT, ref. REN 2001-1495, and European Project METRI (Marine Environment Test and Research Infrastructure) EEC HPRI-CT-2001-00156. The authors are indebted to all partners of MISPEC project for their kind help during the development of this work, especially IFREMER and IO-PAS, and to Hans Amann and Jens Pfannkuche from MAT-TUB (Maritime Technology-Technical University of Berlin) for providing the CTD data during the real field measurements campaign.
 Lewis E L and Perkin R G 1978 Salinity: its definition and calculation J. Geophys. Res. 83 466–77.  Poisson A 1980 The concentration of KCl solution whose conductivity is that of standard seawater (35‰) at 15 ◦C IEEE J. Ocean. Eng. OE-5 29–32.  Dakin J and Culshaw B 1988 Optical Fiber Sensors: Principles and Components (London: Artech House).  Mignani A G and Lef`evre H C (ed) 2000 Proc. 14th Int. Conf. on Optical Fibre Sensors (Venice), Proc. SPIE 4185.  Esteban O´ , Navarrete M C, Gonza´lez-Cano A and Bernabeu E 1999 Measurement of the degree of salinity of water with a fiber-optic sensor Appl. Opt. 38 5267–71.  Zhao Y and Liao Y 2002 Novel optical fiber sensor for simultaneous measurement of temperature and salinity Sensors Actuators B 86 63–7.  Zhao Y, Zhang B and Liao Y 2003 Experimental research and analysis of salinity measurement based on optical techniques Sensors Actuators B 92 331–6.  Gentleman D J and Booksh K S 2006 Determining salinity using a multimode fiber optic surface plasmon resonance dip-probe Talanta 68 504–15.  Austin R W and Halikas G 1976 The index of refraction of seawater SIO/University of California. SIO Ref. 76-1 (Scripps Institution of Oceanography, La Jolla, CA, 1976).  Millard R C and Seaver G 1990 An index of refraction algorithm for seawater over temperature, pressure salinity and wavelength Deep-Sea Res. 37 1909–26.  Cong J, Zhang X, Chen K and Xu J 2002 Fiber optic Bragg grating sensor based on hydrogels for measuring salinity Sensors Actuators B 87 487–90.  Stanley E M 1971 The refractive index of seawater as a function of temperature, pressure and two wavelengths Deep-Sea Res. 18 833–40.  Rusby J S 1967 Measurement of the refractive index of seawater relative to Copenhagen standard seawater Deep-Sea Res. 14 427–39.  Minato H, Kakui Y and Nishimoto A 1989 Remote refractive index difference meter for salinity sensor IEEE Trans. Instrum. Meas. 38 608–12.  Pereira D, Frazao O, Ferreira J, Dias I, Dias J M, Teixeira M, Vaz N, Quintela A, Lopes J F and Santos J L 2005 Advanced optical technologies for monitoring estuaries and coastal environments Ciencias Marinas 31 275–84.  Schmidt H, Nguyen B H, Pfannkuche J, Amann H, Kronfeldt H D and Kowalewska G 2004 Detection of PAHs in seawater using surface enhanced Raman scattering (SERS) Mar. Pollut. Bull. 49 229–34.  Lucht S, Murphy T, Schmidt H and Kronfeldt H D 2000 Optimised recipe of sol–gel based surface-enhanced Raman scattering (SERS) substrates J. Raman Spectrosc. 31 1017–22.  Quan X and Fry E S 1995 Empirical equation for the index of refraction of seawater Appl. Opt. 34 3477–80.  Alonso R, Villuendas F, Tornos J and Pelayo J 1993 New ‘in-line’ optical-fibre sensor based on surface plasmon excitation Sensors Actuators A 37–38 187–92.