RADIATIVE-TRANSFER MODEL FOR RELATING NEAR-INFRARED AND MICRONAIRE MEASUREMENTS OF COTTON FIBERS

Assessing cotton fiber quality has become increasingly important. Spec trophotometric reflectance measurements have shown promise in assessin g fiber fineness and maturity. A technique is proposed herein in which cotton sample reflectance is related to electromagnetic theory with a radiative transfer approach. Cotton fibers are assumed to be cylindri cal in shape. All calculations are performed assuming a wavelength of 2000 nm. It is shown that reflectance can be approximated as a functio n of the scattering and extinction coefficients of cotton. These coeff icients are related to the more fundamental parameters of fiber radius , refractive index, and absorption index by way of the Lorenz-Mie theo ry. Different values of radius, refractive index, and absorption index are input to an electromagnetic wave model to predict reflectances. C omparing calculated results and spectrophotometric data is limited bec ause the scattering phase function of cotton fibers is unknown at pres ent. This is left to another study. However, results hold that most of the variation in reflectance emanates from changes in absorption inde x, while some variation comes from changes in radius. Uncertainties in refractive index have very little influence on reflectance. The effec t of change in radius is heightened at low values of absorption index. Assuming that absorption by cotton fibers increases with maturity, it was concluded that the high correlations between near-infrared reflec tance (NIR) measurements and Micronaire measurements are much more rel ated to maturity than to fiber fineness. The radiative transfer approa ch proved quite useful in exposing some of the complex physical relati onships involved.