Estimating Leaf Chlorophyll Concentration of Erectophile Crops Canopies from Multi-spectral Synthetic Data

A comparison of the sensitivity to leaf chlorophyll concentration in erectophile crops canopies is conduced by the analysis of a large synthetic dataset for the newly proposed broad-band OCVI (Optimized Chlorophyll Vegetation Index) and for several narrow-band vegetation indices (VI) specifically proposed as leaf chlorophyll estimators (i.e.: TCARI - Transformed Chlorophyll Absorption in Reflectance Index CARI, TCARI/OSAVI ratio - TCARI/Optimized Soil Adjusted VI - and REIP, Red Edge Inflection Position). The values of the broad-band OCVI correction factor, incorporated to take into account crop and soil types, sensor spectral resolution and scene sun zenith angle, are obtained for SPOT bandwidths using sun elevation and using the slope of the green-red soil line as a practical indicator of the soil spectral behaviour. Synthetic data are obtained by using in the direct mode the coupled PROSPECT+SAILH leaf and canopy reflectance models. Changes in sensitivity of a VI over the range of chlorophyll concentration are analysed, in addition to traditional regression-based statistics, by using a sensitivity function obtained according to the method proposed by Ji and Peters (2007). The broad-band Chlorophyll Vegetation Index outperformed as a leaf chlorophyll estimator at the canopy scale narrow-band VI, with the exception of the TCARI/OSAVI ratio for high solar elevation, wet soils and low leaf chlorophyll concentrations.