Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/27/2005
Publication Date: 7/17/2005
Citation: Qin, J., Lu, R. 2005. Determination of the optical properties of turbid materials by hyperspectral diffuse reflectance. ASAE Annual International Meeting Proceedings. Paper No. 053068. Interpretive Summary: Absorption and scattering are two basic phenomena when light is incident upon a turbid food sample. Quantitative determination of absorption and scattering coefficients, two fundamental optical properties, is crucial for understanding the interaction of light with turbid food materials and for developing effective optical techniques for quality inspection of horticultural and food products. Because of technical difficulties, we still do not have an optical property database for most food and agricultural products. This paper reports on the development of a novel noninvasive technique for determining the absorption and scattering coefficients of turbid agricultural products, including fruits and vegetables. A hyperspectral diffuse reflectance technique was developed to acquire light scattering from turbid samples in the visible and near-infrared spectral range. Hyperspectral imaging is a technique that acquires both spectral and spatial information from an object. Model samples with known optical properties that are similar to those of apples were created to test and evaluate the technique. Light scattering from the model samples was described by a mathematical model, from which absorption and scattering coefficients were obtained over the spectral range between 500 nm and 750 nm. The hyperspectral diffuse reflectance method accurately measured the scattering properties of the model samples. However, improvements are still needed for measuring the absorption properties of turbid samples. Successful development of the technique will provide researchers with a new tool for rapid, noninvasive determination of optical properties of fruits and other agricultural products and help engineers in designing more effective and efficient optical systems for quality evaluation of food and agricultural products.
Technical Abstract: This research was to develop a sensing technique for determining the optical properties of turbid food and agricultural products. Twenty four liquid simulation samples with absorption and reduced scattering coefficients similar to those of apples were created from absorbing dyes and fat emulsion scatterers. A hyperspectral imaging system was used to acquire scattering images of the steady-state diffuse reflectance from the simulation samples over the spectral region between 450 nm and 1,000 nm. The hyperspectral reflectance data were analyzed by using an analytical diffusion theory model for a homogeneous semi-infinite medium. A curve fitting algorithm was used to extract the absorption and reduced scattering coefficients in the wavelength range from 530 nm to 730 nm using the spatial profiles covering the source-detector separations from 1.8 mm to 9.9 mm. The average fitting error for the reduced scattering coefficient was 7.4%, whereas errors for the absorption coefficient were large. Further improvements in data analysis are needed for accurate determination of both scattering and absorption coefficients.