The influence of architectural and spectral parameters of a tropical forest canopy under its reflectance described by IBIS model

Abstract

Studying and monitoring vegetation is the key to understand the current climate pattern in both regional and global scales. Dynamical Vegetation Models (DVM) are useful tools in biome studies, since they are based on physical principles as well as on initial and boundary conditions. They are able to obtain evidences of factors that influence the modeled environment, predicting future vegetation behavior and, in association with other models, making future predictions of vegetation influence on climate or the effect of climate change on vegetation itself. In particular, reflectance models are part of DVMs. Some studies have attempted to identify canopy elements influence on the vegetation cover albedo, obtaining the best configuration of parameters to be used. Important parameters are estimated from the reflectance in specific spectral bands. Thus, the objective of this study was to evaluate the IBIS model - Integrated Biosphere Simulator performance running it at three bands - red, near infrared, and blue, corresponding to the bands 1, 2 and 3 of the MODIS sensor, onboard of the TERRA and AQUA satellites. The sensitivity to optical parameters (leaf reflectance) and architecture (slope of the leaves) of the canopy was also evaluated. These optical and architectural parameters were calibrated according to the surface reflectance and vegetation index from MODIS for the Cuieiras Reserve (K34). The sensitivity analysis indicated a strong influence of the upper canopy parameters. The parameters combination that minimizes the RMSE of EVI - Enhanced Vegetation Index (RMSE = 0.0245) were the slope of the upper canopy leaves χup = 0.92, reflectance from the upper canopy leaves in the blue bandρblue-up = 0.0162, red bandρred-up = 0.0466 and near infrared bandρnir-up = 0.4427. © 2012 Sociedade Brasileira de Geofísica.