Identification of crop canopy geometry based on multi-temporal and bidirectional canopy reflected spectrum

摘要

Investigations have been made on identification of erective, middle and horizontal varieties by multi-temporal and bidirectional canopy reflected spectrum in wheat. Reflectance at near infrared 800nm of loose varieties was higher than that of erective varieties at jointing stage. The combination of ratio and canopy reflectance at 800 nm at erecting stage could be used for identification of crop geometry based on the multi-temporal data. There are two methods for identification crop geometry parameters, one was by the bidirectional canopy reflectance and different wavebands and view angles, the bidirectional reflectance of visible and near infrared bands at 15°, 30°and 45° field of view for the main viewing plane could be used for identification of plant structural types based on bidirectional data. For erective varieties, the bidirectional canopy reflectance at near infrared was f45° > f15° > f30°, at visible band was f45° > f15° ≈ f30°; For middle varieties, the bidirectional canopy reflectance at near infrared and visible band was f15° > f45°> 130°; For horizontal varieties, the bidirectional canopy reflectance at near infrared and visible band was f45° > f30° > f15°.The other method was by inversion of semi-empirical BRDF models. The structure parameter sensitive index (SPEI) which based on the weight for the volumetric kernel (f_(vol)), the weight for the geometric kernel (f_(geo)), and the weight for constant corresponding to isotropic reflectance (f_(iso)) was defined in this study for crop geometry identification. SPEI was proved to be more sensitive to identify crop geometry structures than structural scattering index (SSI) and normalized difference f-index (NDFI), SPEI could be used to distinguish erective, middle and loose geometry varieties. So, it is feasible to identify horizontal, middle and erective varieties of wheat by multi-temporal and bidirectional canopy reflected spectrum.