Terrasar-X Based Assessment of Canopy Structure Along a Land Use Intensity Gradient in Central Sulawesi, Indonesia

Abstract

The present study investigates the relations between statistical measures of TerraSAR-X backscatter coefficients and field inventory measures for tropical agroforestry systems in Central Sulawesi, Indonesia. The background of the study is to evaluate the potential of spaceborne SAR missions for the spatially explicit estimation of horizontal and vertical structure elements of land use systems in tropical regions in order to assess quantitative variables for ecological modeling purposes. Three TerraSAR-X dual-polarized high resolution Spotlight scenes were acquired in the first half of September 2008 and radiometrically processed to normalized backscatter values. The results of the correlation analysis reveal a number of significant statistical relations between first order statistics of the backscatter coefficients (e. g. coefficient of variation) and canopy variables (e. g. leaf area index, R= 0.8) as well as tree geometric variables (e. g. diameter at breast height, R= 0.59) at the plot level. For other variable, strongest relations are found when only the upper canopy layers (shade trees) are selected for analysis (e.g., stem height, R= 0.76; canopy cover, R= 0.62). The findings support the hypothesis that X-band radar signals are able to deliver estimates of the vertical component of tropical vegetation stands especially in land use systems that are characterized by distinct boundaries of vegetation layers (e.g. cash crops under shade trees) like the cacao agroforestry systems in Indonesia.