Using hyperspectral remote sensing data for retrieving total canopy chlorophyll and nitrogen content

In this study the estimation of canopy chlorophyll and nitrogen content using hyperspectral reflectance data is presented. A large range of canopies was simulated using the PROSAIL radiative transfer model at a 1 nm sampling interval. Several widely used chlorophyll-related vegetation indices were tested in estimating canopy chlorophyll content. Subsequently, tests with field data were performed for 40 sampling locations within an extensively grazed fen meadow using an ASD FieldSpec spectrometer. PROSAIL simulations showed that the red edge chlorophyll index (CI_{red edge}) was the best index that was linearly related to the canopy chlorophyll content over the full range of potential values (R² = 0.94, RMSE = 0.29 g.m^-2). At the study site nitrogen content has been measured instead of chlorophyll. The CI_{red edge} was found to be a good and linear estimator of canopy nitrogen content (R² = 0.67, RMSE = 0.99 g.m^-2). Results demonstrate that CI_{red edge} can be applied across species with widely varying leaf structure without the necessity for extensive calibration for each species.