Forest and Water Mapping with TanDEM-X

Abstract

The interferometric SAR dataset acquired by TanDEM-X to generate a global Digital Elevation Model (DEM), covering at least twice the complete Earth’s mass, represents a unique data source to derive geo-information products at a global scale. Moreover, it gives the opportunity to monitor Earth’s dynamics at a local scale by the acquisition and analysis of time series. In the bistatic TanDEM-X system, characterized by the absence of temporal decorrelation, the volume correlation factor, which quantifies the amount of decorrelation due to scattering from a volume, is a good indicator to distinguish between forest and non-forest areas. A first global TanDEM-X forest/non-forest map at 50 m resolution, using such technique, has been released in May 2019 and is free downloadable for scientific use. In our study, we have further exploited the TanDEM-X bistatic data to determine deforestation in the past years. By applying an adaptive image segmentation approach, it has been possible to improve the forest/non-forest classification and to identify the detection of clear-cuts. In the case of water mapping with TanDEM-X, we are in the process of generating a global Water Body Layer (WBL), using the interferometric coherence of TanDEM-X interferometric acquisitions as the main input. The proposed approach takes also into account the geometric properties of SAR acquisition scenes, in order to mitigate the effects of geometric distortions, such as shadow and layover, and to improve the discrimination between water bodies and vegetated areas of low coherence.