A SIMPLE FIBEROPTIC SENSOR TO DETECT THE PENETRATION OF MICROSENSORS INTO SEDIMENTS AND OTHER BIOGEOCHEMICAL SYSTEMS

We have developed a simple and mechanically robust fiberoptic microsen sor that enables optical detection of the sediment-water interface at a spatial resolution of <50 mu m The sensor measures with a tapered op tical fiber the increased backscatter of near-infrared light near the sediment surface. To determine the sediment surface position independe nt of ambient light conditions, we developed a miniaturized opto-elect ronic system with an intensity-modulated laser diode (780 nm) as the l ight source and a photodiode as the detector. Laboratory tests of our system were done with artificial as well as with various natural sedim ents and biofilms. Fiberoptic microsensors for surface detection can b e combined easily with both electrochemical and optical microsensors f or oxygen or other reactive species.