Remote Sensing Analysis of High-Density Canopy fAPAR Considering the Absorption Ratio of Senescent Leaves

The fraction of absorbed photosynthetically active radiation (fAPAR) is an important biophysical characteristic in models of vegetation productivity. Synoptic estimation of fAPAR has been performed by using Normalized Difference Vegetation Index(NDVI) as a linear proxy of fAPAR. However, in high-density canopies, the sensitivity of NDVI to fAPAR is reduced. The NDVI/fAPAR relationship is analyzed in high-density rice in this paper. In addition, we combine the absorption ratio of senescent leaves and green leaves in the photosynthetically active radiation (PAR) region, re-determines the meaning of green fAPAR, and analyzes the sensitivity of green fAPAR under different nitrogen treatments. Moreover, other more effective alternative vegetation indices such as Wide Dynamic Range Vegetation Index (WDRVI) and absorption coefficient of PAR (α
PAR
) by remote sensing are also utilized to evaluate changes in green fAPAR.