Study on bidirectional reflectance distribution function features of wheat with different plant type

Abstract: Canopy structural property is a noticeable factor that exerts a certain influence on canopy bidirectional reflectance, thus it is primarily significant to detect a crop structure signature to refer to quantified remote sensing. This paper analyzed the variations in bidirectional reflectance of erective wheat J411 and loose wheat Z9507 under different solar zenith angles and viewed zenith angles in a solar principal plane. What's more BRDF (Bidirectional Reflectance Distribution Function) features for the two varieties were explored by exploiting six BRDF shape indictors in a red band (680 nm) and NIR (Near Infrared) band (860 nm) based on the semi-empirical BRDF kernel model and 25 field-measured multi-angle datasets from three years during the year 2003-2004、2004-2005, and 2008-2009. The results showed that during the jointing stage, the sensitive stage to identify canopy geometry, Z9507 conceived a larger bi-NDVI (Bidirectional Normalized Difference Vegetation Index) than J411 in a solar principal plane, that means the loose wheat held a larger coverage than the erective variety. Performances of six anisotropic indices differed in varieties and bands. For the erective variety, both ANIF and ANIX in the red band were slightly higher than the loose wheat, while in the NIR band the values for loose wheat exceeded the erective variety. Meanwhile, a similar variation trend presented for the two varieties was that the ANIX was always higher than the ANIF in two bands and values of the two indices in NIR band were larger than that in the red band for both two varieties. Referring to AFX, it displayed a different variation trend compared with ANIF and ANIX. Its values fluctuated around 1. In the red band, the AFX for two varieties were almost less than 1, and in the NIR band were beyond 1, which explicitly depicted the dominance of canopy geometric scattering in the red band and volumetric scattering in the NIR band. Moreover, in the red band the AFX of erective wheat was slightly higher than the loose wheat, while in the NIR band the AFX of loose wheat outweighed erective wheat. Therefore, it is concluded that the geometric weights of an erective variety in the red band are more significant than the loose variety, indicating a stronger geometric effect in the red band for erective wheat; and in the NIR band higher volumetric weights are for the loose variety, suggesting a stronger volumetric effect in the NIR band for loose wheat. Finally, it was illustrated that the anisotropic indices are more capable and applicable to extract crop canopy structural information.