Towards Red-edge Positions Less Sensitive to Canopy Biophysical Parameters Using Prospect-sailh Simulated Data

The position of the inflexion point in the red edge (680 nm to 780 nm), termed the red-edge position (REP) has been used as a measure to estimate foliar chlorophyll or nitrogen content. In this study, we assessed the utility of a new technique for extracting the REP, the linear extrapolation method recently proposed by Cho and Skidmore [Remote Sens. Environ. (in press)]. The assessment was based on synthetic canopy reflectance spectra using the PROSPECT and SAILH models. The models were parameterised to represent a wide range of canopy characteristics. REP calculated by the new method involving wavebands at 680, 694, 724 and 760 nm yielded the highest correlation with leaf chlorophyll content (R = 0.75) and with minimal effects of leaf and canopy biophysical confounders such as LAI, leaf inclination distribution and leaf dry matter content compared to traditional techniques including the wavelength of maximum first derivative, linear interpolation, inverted Gaussian modelling and third order polynomial fitting, respectively. However, the advantage of using the new method compared to the other REP extraction techniques diminishes with increasing bandwidth. In summary, the linear extrapolation technique shows high potential for leaf chlorophyll estimation with radiative transfer models. The efficacy of the technique under field conditions needs to be established.