Optical Transmittance of a Rice Leaf via Ray Tracing

Opticalreflectance from a plant leaf increases in response to stress and disease. Previous studies at the University of Arkansasat Little Rock found that, while the reflectance from a rice leafincreased withincreased salinity,reflectance changes could not be used to differentiate one stress or disease from another. The objective of this studyis to characterize the angular distribution of opticaltransmittance for a healthyrice leaf using a ray tracing technique and assuming a three-media optical model. The ultimate goal is to relate this distribution to specificplant pathologies. Three rays are traced through the cross sec- tion of a healthyrice leaf by applying laws of geometric optics and considering air, cell wall, and chloroplast as media. The angular distribution of transmittance is calculated for each ray trace. Leiis defined as the length of irradiated upper epidermal surfaceleading to a continuous transmittance Tbi(0)at the bottom surface.The total transmittance is defined as the sum over i of Tbi(6).A6iis defined as the angle over which Tbi(9)extends and (0j - 6i) is defined as the angular differencebetween the bisector of A0iand the bisector of A0j.The probability density functionspdf(A0) and pdf(0j-0i) are defined and shown to have diagnostic potential.