Determining the Optical Properties of Two-Layer Turbid Materials Based on Spatially Resolved Diffuse Reflectance

Authors: CEN, HAIYAN - Michigan State University; Lu, Renfu

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 4/28/2009
Publication Date: 6/21/2009
Citation: Cen, H., Lu, R. 2009. Determining the Optical Properties of Two-Layer Turbid Materials Based on Spatially Resolved Diffuse Reflectance. Proceedings of the ASABE Annual International Meeting. Paper No. 095769.

Interpretive Summary: Fruits, such as apples, have a surface layer (skin) whose properties and characteristics are distinctly different from those of the subsurface layer (flesh). To effectively measure internal quality of fruit, it is desired to separately quantify properties of fruit skin and flesh. This research was therefore aimed at developing a new method and technique to determine the optical properties of turbid food products, such as fruits, that are composed of two distinct layers of homogeneous materials in order to more accurately measure internal quality. A mathematical model along with computer algorithm was developed to simulate light transfer in two-layer media and extract optical properties from the media. The two-layer model was validated through both computer simulations and experimental data obtained from specially created model samples with known optical properties. The model achieved acceptable accuracies compared with computer simulation results. Relatively large errors were obtained in determining the optical properties of the model samples. This research showed that the method could be used to measure the optical properties of each layer in two-layer products such as fruits. However, to make the method practical, further improvements in computer algorithm and data acquisition technique are needed. Successful development of such method would enable more accurate assessment of internal quality of fruits and food products.

Technical Abstract: Hyperspectral imaging-based spatially resolved technique is useful for determining the optical properties of fruits and food products that are homogeneous. To better characterize fruit properties and quality attributes, it is necessary to consider fruit to be composed of two homogeneous layers, i.e., skin and flesh. This research was aimed at developing a nondestructive method to determine the spectral absorption and scattering properties of two-layer turbid materials with characteristics of fruit. An inverse algorithm for a two-layer diffusion model was developed for extraction of optical properties from the spatially resolved diffuse reflectance data acquired using a hyperspectral imaging system. The diffusion model and inverse algorithm for determining the optical properties of two-layer turbid media were validated with Monte Carlo simulations and experimental measurements from model samples with the optical properties resembling those of fruit. The average errors of determining two and four optical parameters were 6.8% and 15.3%, respectively, for Monte Carlo reflectance data. Moreover, the optical properties of the first layer of the model samples were determined with errors of less than 23.0% for absorption coefficient and 18.4% for reduced scattering coefficient. The two-layer diffusion model coupled with the hyperspectral imaging-based spatially resolved technique has the potential to measure the optical properties of such turbid materials as fruits and food products.