We investigated the hyperspectral response of controlled mixed algal cultures containing two algal species at a time in transmittance mode to evaluate the response of a laboratory-based hyperspectral imaging system (HIS), as well as the validity of a linear spectral unmixing method in determining the composition of the mixed cultures. The ultimate goal of this project was to apply linear spectral unmixing based on linear mixing models used to predict the abundance or percent composition of algal species (endmembers) in mixed algal cultures. In this work, we compared the linear spectral unmixing results with the actual composition of the algal mixtures to assess the prediction error based on the difference between the actual concentrations and computed concentrations of algae.
By using linear unmixing, linear interactions among the spectra from individual endmembers or pure algae spectra were assumed. A secondary goal of the project was to demonstrate the linear trends associated with Beer-Lambert Law and changing path length in transmission mode to allow the computation of optical properties such as the absorption coefficient using the gradient in linear logarithmic plots from hyperspectral data.Changes in the spectral response of HIS to variations in volume and combinations of algae concentrations in transmission mode are presented. Equipment used, experimental details, data acquisition, and data conditioning are described in Section 2. The application of linear spectral unmixing to predict percent composition of algal mixtures is described in Section 3.
In addition, Beer-Lambert’s Law and its implementation to investigate optical properties, such as the absorptivity is presented in Section 3. Experimental results and analysis of HIS’ response in differentiating algae samples and volumes are also presented in Section 4 followed by discussion and conclusions.2.?Instrumentation, Experiments, and Data PreprocessingThe work presented here can be separated into data acquisition, data conditioning, spectral analysis for predicting algal composition of the mixtures and for computing prediction errors, and finally application of Beer-Lambert’s Law to investigate optical properties based on changing path lengths. The hyperspectral imaging system, data acquisition, noise characterization and data conditioning (preprocessing) are described in this section.
2.1. Hyperspectral Imaging SystemFigure 1 represents the hyperspectral imaging system in transmission mode. In this configuration, the halogen broadband diffuse light source (EKE 21V 150W) illuminates the sample from the bottom. After interaction with the sample, the transmitted light is collected by the camera lens, fed into a spectrophotometer, Cilengitide and captured by the CDD line-scan camera, which, all together form the hyperspectral imaging system (Hyperspec? VNIR P-Series Imaging Spectrometer, Headwall Photonics, Fitchburg, MA, USA) [32].Figure 1.