Raman
Spectroscopy is no longer exclusively a laboratory analytical technique. It
has become a very promising way for chemical and environmental monitoring in
the undersea world.
Increasing concern over the natural environment has prompted regulatory bodies to enforce continued monitoring of coastal areas and estuaries. To meet this challenge, it has been necessary to develop marine equipment to:
- Monitor accidents and spills
- Act as alarm sensors
- Support oceanographic studies
Raman goes underwater
Marine Raman spectroscopic analysers have been designed for underwater operation in any marine or deep-sea environment from shallow estuaries to deep water trenches.
Pollution monitoring
Under the framework of two European projects in which HORIBA Jobin Yvon and partners IFREMER have participated (EU SOFIE N°MAS3-CT97-0157) & EU MISPEC N° EVK3-CT-2000-00045), feasibility investigations and method development studies were successfully conducted on the application of Raman spectroscopy to marine environment monitoring. Through several sea trials along the European coasts the first results of Raman marine analysis were obtained.
The major aims of this project were to investigate hydrocarbon pollution in the world’s oceans, specifically PAHs (Polycyclic Aromatic Hydrocarbons) - chemicals which have been found to be particularly harmful for the environment.
Concentrations of these pollutants is often extremely low, hence it is necessary to choose a technique appropriate to carry out such a demanding analysis. Thus, sensitivity enhancements given by SERS (Surface Enhanced Raman Spectroscopy) offered the real possibility to obtain remote measurements of such dissolved form organic compounds within the world’s oceans.
- Minerals
Raman spectroscopy is well established for the analysis of geological and mineralogical samples such as ores, gemstones and even meteorites. Hence, it is a candidate technique for the in situ identification of minerals found on the sea floor. Using the same core technology as the environmental monitoring Raman system, further studies have been planned to investigate methane hydrates and cold seep ecosystems by Raman spectroscopy which should provide important information on seafloor carbonates related to the micro and macro fauna.
The System Technology
Based on the patented and novel axial spectrograph technology from
HORIBA Jobin Yvon, the instrument is centred on a core unit which contains
the spectrograph, detector, the selected laser source and special electronics
for communication and data transmission for its remote operation. The measurements
themselves are achieved through fibre optic probes, linked to the core unit
by the way of watertight bundles of optical fibres. All the underwater equipment
and housings are pressure tested and optimised for applications down to 6000m
depth. The complete analyser system can be operated on simple towed vehicles,
vertical profilers or on sub-sea robots such as ROV (Remotely Operated Vehicles).
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