欧亚国际

最近，来自欧洲和中国的科学家利用无人机和Airphen多光谱相机在知名期刊Remote Sensing of Environment发表了题为Impact of the reproductive organs on crop BRDF as observed from a UAV的文章，主要研究了成熟期冠层结构和生理变化对BRDF的影响。部分科学家来自法国Hiphen公司，Hiphen是世界知名的遥感表型设备以及技术服务供应商。

Impact of the reproductive organs on crop BRDF as observed from a UAV  

Wenjuan Li a, b, 1, *, Jingyi Jiang a, d, 1, Marie Weiss a, Simon Madec a, Franck Tison a, Burger Philippe c, Alexis Comar b, Fr´ed´eric Baret a 

a INRAE, Avignon Universit´e, UMR EMMAH, F-84000 Avignon, France

b HIPHEN, F-84000 Avignon, France

c INRAE, UMR AGIR, Toulouse, France

d Research Center of Forest Management Engineering of State Forestry and Grassland Administration,  Beijing Forestry University, 100083  Beijing, China 

ABSTRACT

Several crops bear reproductive organs (RO) at the top of the canopy after the flowering  stage, such as ears for wheat, tassels for maize, and heads for sunflowers. RO present specific architecture  and optical  properties as compared to leaves and stems, which may impact canopy reflectance. This study aims to understand and quantify the influence of RO on the bi-directional variation  of canopy reflectance and NDVI.

Multispectral camera observations from a UAV were completed over wheat, maize, and sunflower just after flowering  when the RO are fully  developed and the leaf layer with  only marginal senescence. The flights  were designed to sample the BRDF with  view zenith angles spanning from nadir to 60◦ and many compass directions. Three flights  corresponding to three sun positions were completed under clear sly conditions. The camera was always pointing to two adjacent plots of few tenths of square meters: the RO were manually removed on one plot, while  the other plot was kept undisturbed. 

Results showed that the three visible bands (450 nm, 570 nm, 675 nm), and in a lesser way the red edge band (730 nm) were strongly correlated. We, therefore, focused on the 675 nm and 850 nm bands. The Bi-Directional Reflectance (BRF) of the canopy without RO shows that  the BRF values were almost symmetrical  across the principal  plane, even for maize and sunflower  canopies with  a strong row structure.  Examination  of the BRF difference between the canopy with  and without RO indicate  that the RO impact canopy BRDF for the three crops. The magnitude of the impacts depends on crop, wavelength and observational geometry. These obser- vations are generally consistent with  realistic  3D reflectance simulations.  However, some discrepancies were noticed, mainly explained by the small magnitude of the RO effect on canopy BRF, and the approximations made when simulating  the RO layer and its coupling with  the bottom canopy layer. We finally  demonstrated that the RO layer impact the estimates of canopy traits such as GAI as derived from the multispectral observations.