Progress in retrieving canopy structural parameters and chlorophyll content using the refined hyperspectral and multi-angle measurement concept and CASI data

摘要

We attempt to test the refined concept of combining multi-angle and hyperspectral remote sensing proposed by [1] using airborne data. The concept proposes a system that acquires hyperspectral signals only in the nadir direction and measures in two additional directions in two spectral bands, red and NIR. It has been successfully demonstrated that the off-nadir hyperspectral simulations could be closely reconstructed based on the nadir hyperspectral reflectance and off-nadir multi-spectral reflectance in red and NIR bands. This is shown using the Compact Airborne Spectrographic Imager (CASI) data acquired over a forested area in the Sudbury region (Ontario, Canada). Through intensive validation using field data, it is demonstrated that the combination of the hotspot and darkspot reflectances has strong response to changes in vegetation clumping. Furthermore, the model inversion using a LUT approach is employed to retrieve chlorophyll content per unit leaf area. In order to explore the impact of clumping on the chlorophyll content retrieval, we compared the results of the inversion based on leaf area index (LAI) and based on effective LAI (Le). In the comparison with the field-measured data, the determination coefficient increases and RMSE decreases when LAI is considered.