  Directional area scattering factor (DASF) is a critical canopy structural
parameter for vegetation monitoring. It provides an efficient tool for
decoupling of canopy structure and leaf optics from canopy reflectance. Current
standard approach to estimate DASF from canopy bidirectional reflectance factor
(BRF) is based on the assumption that in the weakly absorbing 710 to 790 nm
spectral interval, leaf scattering does not change much with the concentration
of dry matter and thus its variation can be neglected. This results in biased
estimates of DASF and consequently leads to uncertainty in DASF-related
applications. This study proposes a new approach to account for variations in
concentrations of this biochemical constituent, which additionally uses the
canopy BRF at 2260 nm. In silico analysis of the proposed approach suggests
significant increase in accuracy over the standard technique by a relative root
mean square error (rRMSE) of 49% and 34% for one- and three dimensional scenes,
respectively. When compared with indoor multi-angular hyperspectral
measurements reported in literature, the mean absolute error has reduced by 68%
for needle leaf and 20% for broadleaf canopies. Thus, the proposed DASF
estimation approach outperforms the current one and can be used more reliably
in DASF-related applications, such as vegetation monitoring of functional
traits, dynamics, and radiation budget.
