Modelling and Synergetic Use of Optical and Microwave Remote Sensing. Report 2:LAI Estimation from Canopy Reflectance and WDVI: A Sensitivity Analysis with the SAIL Model

摘要

After reviewing potential vegetation indices and reflectance models for Leaf AreaIndex (LAI) estimation of agricultural crops, a sensitivity analysis is performed with the SAIL reflectance model towards the influence of disturbing factors on the LAI estimation from canopy reflectance and WDVI (Weighted Difference Vegetation Index). The WDVI was developed as part of the CLAIR model for correcting the near infrared reflectance for soil background. From the SAIL simulations it is concluded that the influence of external factors (soil reflectance, ratio diffuse/total irradiation and solar view geometry) will not pose a large problem for the relationship between LAI and WDVI. However, crop parameters other than LAI have a significant influence on the relationship between WDVI and LAI. Actual information on these parameters mostly is lacking. Since often these parameters (such as leaf inclination, leaf reflectance and leaf transmittance) change only gradually during crop growth, their influence is caught in the two empirical parameters of the CLAIR model, which are estimated from a training set.