Optical Remote Sensing using Raman Spectroscopy
Optical remote sensing of water temperature using Raman spectroscopy
Knowledge about water temperature and salinity, in both freshwater and marine environments is of great importance in fields such as oceanography, climate change and environmental science. It is vital to validate hydrologic modelling, to provide habitat information about plant/animal species in waterways, and to optimise underwater communications. Helen Pask, Chris Artlett, Caro Derkenne and Andrea Ribeiro have been engaged in laboratory and field studies to develop new methods for rapid depth-resolved mapping of water temperature and salinity profiles.
Our techniques are based on stimulated Raman scattering, in which a portion of laser light (eg. green) interacts with water molecules to produce a small amount of “Raman-shifted” light (eg. red). The spectral content of this red light depends on temperature and salinity. We designed a simple optical instrument comprising an excitation laser (532nm) and 3 spectral channels defined by optical filters with photomultiplier detection. Multivariate analysis is applied to optimally determine temperature and salinity from measured signals, while laser ranging methods enable depth profiling.
Raman spectra with changing temperature and fixed salinity (15 PSU).
Figure 3 – Raman spectra with changing salinity and fixed temperature (25 oC).
The setup is compatible with a variety of platforms: shore-based, ship-based, underwater or airborne, and will provide data in near-real time. The technology is similar to that used for laser airborne-depth sounding, and the information extracted can complement depth measurements.
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A recent publication can be found at: https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-25-31844
Some images from the field test of the equipment.