Estimation of spruce needle-leaf chlorophyll content based on DART and PARAS canopy reflectance models

摘要

Needle-leaf chlorophyll content (Cab) of a Norway spruce stand was estimated from CHRIS-PROBA images using the canopy reflectance simulated by the PROSPECT model coupled with two canopy reflectance models: 1) discrete anisotropic radia- tive transfer model (DART); and 2) PARAS. The DART model uses a detailed description of the forest scene, whereas PARAS is based on the photon recollision probability theory and uses a simplified forest structural description. Subsequently, statisti- cally significant empirical functions between the optical indices ANCB 670 − 720 and ANMB 670 − 720 and the needle-leaf Cab content were established and then applied to CHRIS-PROBA data. The Cab estimating regressions using ANMB 670 − 720 were more robust than using ANCB 670 − 720 since the latter was more sensitive to LAI, especially in case of PARAS. Comparison between Cab esti- mates showed strong linear correlations between PARAS and DART retrievals, with a nearly perfect one-to-one fit when using ANMB 670 − 720 (slope = 1.1, offset = 11 μ g · cm − 2 ). Further com- parison with Cab estimated from an AISA Eagle image of the same stand showed better results for PARAS (RMSE = 2.7 μ g · cm − 2 for ANCB 670 − 720 ;RMSE = 9.5 μ g · cm − 2 for ANMB 670 − 720 )than for DART (RMSE = 7.5 μ g · cm − 2 for ANCB 670 − 720 ;RMSE = 23 μ g · cm − 2 for ANMB 670 − 720 ). Although these results show the potential for simpler models like PARAS in estimating needle-leaf