Submitted to: Applied Optics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2006
Publication Date: 11/10/2006
Citation: Qin, J., Lu, R. 2006. Hyperspectral diffuse reflectance for rapid, noncontact determination of the optical properties of turbid materials. Applied Optics. 45(32):8366-8373.
Interpretive Summary: Absorption and scattering are two basic phenomena when light interacts with turbid food materials. Light absorption is related to chemical constituents of the material, whereas light scattering is influenced by structural properties (e.g., density and cellular structures). Measurement of absorption and scattering properties is important for understanding light interaction with food and agricultural materials and for the development of effective optical techniques to measure compositional and/or structural related properties. Several techniques are currently available for measuring the spectral absorption and scattering properties of biological materials. However, these techniques are generally too expensive, difficult to perform measurements and inefficient, which make them unsuitable for food and agricultural products. This paper reports on the development of a hyperspectral imaging technique for rapid determination of spectral absorption and scattering properties from turbid materials. Hyperspectral imaging enables simultaneous acquisition of spectral and spatial information from a sample over a specific spectral range. Experimental tests of the hyperspectral imaging system demonstrated that the technique achieved good measurements of both absorption and scattering properties for the model samples of known optical properties with the average errors of 12% or lower, which are comparable to other techniques currently available. Compared to other techniques, the hyperspectral imaging technique is fast, noncontact and easy to use, thus making it especially useful for food and agricultural products. The technique gives researchers an important tool for determining the optical properties of a range of food products including fruits and vegetables, which are largely absent in the literature. The technique can also be directly used for quality evaluation of turbid liquid and solid food products.
Technical Abstract: This paper presents a method and technique of using hyperspectral diffuse reflectance for rapid determination of the optical properties of turbid media. A hyperspectral imaging system in line scanning mode was used to acquire spatial diffuse reflectance profiles from liquid phantoms made up of absorbing dyes and fat emulsion scatterers over the spectral range 450-1000 nm instantaneously. The hyperspectral reflectance data were analyzed by using a steady-state diffusion approximation model for semi-infinite homogeneous media. A calibration procedure was developed to compensate the nonuniform instrument response of the imaging system, and a curve fitting algorithm was used to extract absorption and reduced scattering coefficients for the phantoms in the wavelength range from 530 nm to 900 nm. The hyperspectral imaging system achieved good measurements of the absorption and reduced scattering coefficients for the phantoms with the average fitting errors of 12% and 7%, respectively. The hyperspectral imaging technique is fast, noncontact and easy in use, which makes it especially suitable for measurement of the optical properties of turbid liquid and solid foods.