This Small Business Innovation Research (SBIR) Phase I project will develop a chlorophyll fluorescence sensor for deployment on a remote operating vehicle (ROV) or towed sled platform. The sensor will correct the measured fluorescence signal for beam attenuation at the blue excitation and the red fluorescence emission wavelengths. The sensor contains a reference channel to measure in situ the total beam attenuation coefficients at these wavelengths. A unique feature of the sensor is a RF modulated blue light-emitting diode (LED) excitation source, coupled with frequency-domain detection electronics. This will permit accurate determination of the optical measurement pathlength with an optical ranging technique. Measured pathlength and the attenuation coefficients then provide total excitation and fluorescence beam attenuation. In addition to being able to determine the corrected fluorescence intensity over a wide range of water optical conditions, the sensor will measure chlorophyll fluorescence lifetime. This feature is critical because it will solve the most fundamental problem that plagues simple chlorophyll fluorescence intensity measurements for determination of biomass, i.e., that chlorophyll fluorescence intensity cannot be directly correlated to microalgal biomass because the fluorescence quantum yield of chlorophyll in vivo is highly variable. Applications are expected in sensors for biological oceanography research and for marine environmental monitoring. In addition to marine application, other potential markets include agriculture, aquaculture, fish farming, plant genetic engineering, on-line process-analysis in bioreactors, and forestry.
