A fast fiber optic spectrofluorometer for Eddy Correlation measurements of benthic flux

Eddy Correlation (EC) is a relatively new technique for determining benthic fluxes to or from freshwater and marine sediments that addresses many of the challenges faced by traditional methods. Based on high-speed, simultaneous and co-located velocity and concentration measurements, EC has been successfully used to measure benthic fluxes of dissolved oxygen in a variety of settings. To expand the range of chemicals whose flux can be measured by this technique, a novel optical fiber spectrofluorometer has been created that is capable of high-speed, high-resolution in situ measurements of fluorescing compounds. This battery-operated spectrofluorometer utilizes an LED for excitation, as well as 1000 um optical fibers to carry light to and from the sensing volume. A tunable monochromator enables the detected emission wavelength to be adjusted; thus, the instrument can potentially be used to target a variety of compounds, as well as to characterize the fluorescent chemical composition of the environment. Emitted light is quantified by photon counting, using a photomultiplier tube coupled to a custom photon-counting circuit board. The instrument is controlled by a Raspberry Pi microcomputer, and is housed in a compact pressure housing for underwater deployment. Used in an eddy correlation setup, this spectrofluorometer will enable benthic flux measurements of a wide range of fluorescing compounds.