Spectroradiometric Monitoring of Nannochloropsis salina Growth

The high productivity of fluidically mixed open ponds for algal biofuel production is accompanied by high environmental and temporal variability. Therefore, a recognized need exists for rapid monitoring of open ponds to quantify algal growth rates, assess algal stress, detect the presence of invading species, and determine the optimum time for harvesting. Multispectral/hyperspectral approaches are now being used to optimize conventional agriculture practices and similar remote sensing techniques can potentially be used for monitoring algal ponds. In this work, we assess the application of remote techniques for algal biofuel production by using a dual-channel spectroradiometer to monitor the laboratory-scale growth of Nannochloropsis salina, a popular microalgal candidate for biofuels. One channel of the spectroradiometer measures the downwelling irradiance while the second channel simultaneously monitors the upwelling radiance, and the reflectance is calculated by ratioing these two signals. A detailed reflectance model is developed to interpret the acquired spectra, enabling a remote assessment the culture's optical depth as well as the relative optical activity of different algal pigments in N. salina. ► Reflectance of an algal culture is measured with a dual-channel spectroradiometer. ► Reflectance model developed with pigment-specific absorption and fluorescence. ► Matching the model to the measurements yields absorption, scatter, and fluorescence. ► Reflectance-derived parameters are consistent with extracted-sample measurements. ► Enables real-time measurement of chlorophyll concentration and algal growth.