EurOCEAN 2000 - Vlaams Instituut voor de Zee

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SPECTROSCOPY USING OPTICAL FIBRES IN THE MARINE
ENVIRONMENT (SOFIE)
Heinz-Detlef Kronfeldt 1 , Heinar Schmidt 1 , Hans Amann 2 , Brian Mac Craith 3 , Michel
Lehaitre 4 , Michel Leclercq 5 , Eusebio Bernabeu 6 , Boris Mizaikoff 7 , Dave Grant 8
1 Optisches Institut, Technische Universität Berlin, Germany; 2 Maritime Technik,
Technische Universität Berlin, Germany; 3 BEST-Centre, Dublin City University,
Ireland;
4 IFREMER, Centre de Brest, France; 5 Jobin Yvon S.A., Villeneuve d’Ascq, France;
6 Departamento de Optica, Universidad Complutense de Madrid, Spain; 7 Institut für
Analytische Chemie, Technische Universität Wien, Austria; 8 HYDROVISION Ltd.,
Aberdeen, Great Britain.
SUMMARY
The SOFIE project is a feasibility study whose aim is to design, construct and test a prototype
instrument for the in-situ detection of selected pollutants and salinity in sea-water. A key issue
is to combine four different spectroscopic methods in one overall instrument to have a versatile
instrument which may be adapted later to other specific needs. To this end four sensors were
developed for specific parameters and adapted to the requirements of the harsh marine
environment. These sensors are being linked to two core instruments which were designed and
built in this project. The final aim is to test the instrument under controlled conditions in flume
tanks and finally in field trials with the instrument settled on an open frame ROV.
INTRODUCTION
Real-time and in-situ sensors offer new possibilities for monitoring and survey of the coastal
zone which are complementary to existing measuring methods traditionally employing
sampling. As some essential parameters to monitor water quality are based on optical methods,
e.g. turbidity, colour, fluorescence of organic pollutants and pigments etc., the idea was to
extend on one hand the possibilities of using optical methods by increasing spectral range and
resolution accessible with one instrument and on the other hand by developing new sensors to
be attached to this spectroscopic core instrument. The key to achieving of this aim is the use of
optical fibres i and an especially designed imaging spectrograph ii . The basic lay-out of such an
system is shown in Fig. 1.
The term “optode”, often also referred to
as “optrode” is derived from optical and
electrode. The optode may be a sensor
using the fibres only for transmission of
the radiation or a section of the fibre
itself may form the sensing area (i.e. a
fibre optic chemical sensor, FOCS).
Fig.1 System of core instrument and optode
If the input fibres of several optodes are arranged at the entrance slit of an imaging
spectrograph the spectra transported by each fibre can be registered simultaneously by a CCD
array detector. This design inherently offers the ability for multiple-parameter detection. In this
context, the issue was to find out what are the specific requirements for each method, how to
combine them and where are the limitations. Another advantage of this optode system is the
flexibility to exchange and add optodes.