Impact of Rice Canopy Structure on Canopy Reflectance Spectra

摘要

Plant canopy reflectance is affected not only by the optical properties of canopy components, but also by canopy structure. In this paper, the radiative transfer model was used to simulate rice canopy bi-directional reflectance to determine its sensitivity to leaf area index (LAI) and inclination. In simulating canopy bi-directional reflectance over 400-940 nm, LAI was changed from 1 to 7 at an increment of 1; leaf inclination was changed from 50° to 85° at an interval of 5°. All other parameters in the model were measured in the field or deduced from references. It is found that with the rise in LAI, nadir reflectance decreases in visible light but increases in near infrared wavelengths. It tends to become stabilized when LAI is sufficiently large (e.g., >4). Decreasing with leaf inclination, canopy nadir reflectance becomes more sensitive to leaf inclination at a larger LAI. At 550nm and 670nm, bi-directional reflectance decreases with LAI regardless of view zenith. At 830nm, it is proportional to LAI over the view zenith angles of -85° - 40°. However, it is inversely related to LAI when it exceeds 3. Similar to nadir reflectance, bi-directional reflectance tends to become stabilized at a larger LAI at all view zeniths.