Estimating biophysical properties of Eucalyptus plantations using optical remote sensing techniques.

The feasibility of the inversion of optical remote sensing products to measure critical biophysical properties of Eucalyptus Forests at regional scales is investigated here. The biophysical variables used were leaf area Index, LAI, Diameter at Breast Height, DBH, Height and Age of Eucalyptus stands pertaining to a combination of different genetic materials (E. urophylla x E. grandis hybrids) and propagating systems (seeds or cuttings) and management system (planting and coppicing). The field sampling was done daily during 3 months, from April to June 1997, and covered 130 stands of minimum size of 9 hectares, within an Eucalyptus farming area of about 800 km(2) centered at 19 degrees S, 42 degrees W, Brazil. The stands ranged from 12 to 84 months old. The measurements of LAI were done using two pairs of LAI-2000 (LICOR) under conditions of diffuse light. The Normalized Difference Vegetation Index, NDVI, and the Soil Adjusted Vegetation Index, SAVI, were derived from a LANDSAT-TM image acquired on June, 5, 1997. Furthermore, a mixture model technique was applied to derive three new parameters: fraction of green vegetation, F-GV, fraction of shadow, F-SH, and fraction of soil, F-S. Regression analysis were done between biophysical variables and remote sensing products. Linear correlation with coefficients of determination, R-2, as high as 0.8 were found between LAI versus F-GV and LAI versus SAVI, on all genetic materials. In general, SAVI was shown to give better estimates of LAI than NDVI, which is explained by the openings in the canopy as the Eucalyptus grow older. The correlation with the other biophysical variables (Height and DBH) were also shown to be significant, although the R2 ranged from 0.4 to 0.6. The correlation between F-GV and SAVI was higher than 90% such that they can be used to estimate Eucalyptus biophysical parameters with the same statistical significance.