A STUDY OF THE RELATIONSHIP BETWEEN RADAR BACKSCATTER AND REGENERATING TROPICAL FOREST BIOMASS FOR SPACEBORNE SAR INSTRUMENTS

The relationship between mean backscattering coefficient, as measured by spaceborne SAR instruments, and the areal density of above-ground b iomass in regenerating tropical forest is investigated for a study are a in the central Amazon basin. Measurements of tree height, diameter, and species composition were made in 1994 in the Tapajos region of Par a State in Brazil in order to estimate the biomass density in 15 widel y distributed sample plots. These plots were chosen so as to character ize homogeneous forest areas representing a range of ages of regenerat ion from new regrowth to mature forest. The mean backscattering coeffi cients of these forest areas, as measured by SAR instruments on the ER S-1 and JERS-1 satellites and by SIR-C on the Space Shuttle, was deter mined so that its dependence on the biomass density of regenerating fo rest at different radar wavelengths and polarizations could be quantif ied. Results confirm the findings of similar studies of different type of forest, and of radar backscatter models, that the longer wavelengt h (L-band) SAR imagery may be used to discriminate between different l evels of forest biomass up to a certain threshold and that cross polar ized backscatter is more sensitive to changes in biomass density. The shorter wavelength (C-band) SAR imagery is limited to differentiating between vegetation and bare soil when it is dry. The biomass density l imit of around 60 tonnes per hectare, above which the L-band backscatt er shows no further sensitivity to increased biomass density, suggests that spaceborne SAR imagery is suitable for estimating the biomass de nsity and determining the extent of cleared and regenerating forest in tropical regions. (C) Elsevier Science, Inc., 1997.