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

Abstract

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">red edge</sub> ) was the best index that was linearly related to the canopy chlorophyll content over the full range of potential values (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.94, RMSE = 0.29 g.m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ). At the study site nitrogen content has been measured instead of chlorophyll. The CI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">red edge</sub> was found to be a good and linear estimator of canopy nitrogen content (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.67, RMSE = 0.99 g.m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ). Results demonstrate that CI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">red edge</sub> can be applied across species with widely varying leaf structure without the necessity for extensive calibration for each species.