Optical Transmittance of a Rice Leaf via Ray Tracing

Optical reflectance from a plant leaf increases in response to stress and disease. Previous studies at the University of Arkansas at Little Rock found that, while the reflectance from a rice leaf increased with increased salinity, reflectance changes could not be used to differentiate one stress or disease from another. The objective of this study is to characterize the angular distribution of optical transmittance for a healthy rice leaf using a ray tracing technique and assuming a three-media optical model. The ultimate goal is to relate this distribution to specific plant pathologies. Three rays are traced through the cross section of a healthy rice 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. Lei is defined as the length of irradiated upper epidermal surface leading to a continuous transmittance Tbi(0) at the bottom surface. The total transmittance is defined as the sum over i of Tbi(theta). Delta thetai is defined as the angle over which Tbi(theta) extends and (thetaj - thetai) is defined as the angular difference between the bisector of Delta thetai and the bisector of Delta thetaj. The probability density functions pdf(Delta theta) and pdf(thetaj -thetai) are defined and shown to have diagnostic potential