Leaf area index dynamics estimate in a watershed through remote sensing techniques

Author(s)

Alexandre Cândido Xavier

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2003-02-04
• Advisor: Carlos Alberto Vettorazzi

Abstract

The biophysical variable Leaf Area Index (LAI) is directly related to the evapotranspiration and the productivity and to estimate it on a regional level, remote sensing techniques can be employed. This work studies the relationship between LAI and spectral vegetation indices (Simple Ratio, SR; Normalized Difference Vegetation Index, NDVI; and Soil Adjusted Vegetation Index, SAVI) and vegetation, soil, and shadow endmember fractions, calculated through Linear Spectral Mixture Modelling (LSMM). The LAI in the field was monthly collected along 2001 with the LAI-2000 equipment for different land covers ( sugar-cane, pasture, corn, eucalypt, and riparian forest). Four Landsat-7/ETM+ images (from January, March, August, and November) were acquired and corrected for atmospheric effects through the 6S model. The maximum LAI value observed in the watershed was 4.90. The sugar-cane LAI presented the greater variation due to the management and characteristics of this crop. It was observed that LAI was better related to the NDVI, although it was not statistically different of the relationship LAI-SR. When LAI-NDVI relationship was analyzed for the four dates, it was verified the NDVI sensitivity to soil brightness and solar zenith angles variation. The IAF explained 57% to 72% of the variability in the NDVI. This relationship was inverted to generate LAI maps for the watershed, being observed a high correlation between mean LAI and precipitation. This work represents the beginning of a study that aims at the evaluation of remote sensing techniques as LAI predictors to future applications in evapotranspiration models. (AU)

• FAPESP's process: 98/14499-5 - Estimation of leaf area index dynamics in a watershed using remote sensing techniques
• Grantee: Alexandre Candido Xavier
• Support Opportunities: Scholarships in Brazil - Doctorate