Tropical Forest Height and Underlying Topography from Tandem-X SAR Interferometry

Abstract

Spaceborne SAR Interferometry (InSAR) has the sensitivity to measure canopy height as well as the underlying topography. However, these measurements are limited by attenuation of the radar wave. In this paper, we refine an interferometric approach that exploits few-look averaged interferograms, a coherent electromagnetic simulator and field inventory data. Both the underlying topography as well as the canopy height (forest mean height, canopy top height) are estimated through a statistical method that relates the true ground position to the statistics of few-look InSAR phase-heights that are simulated using the simulator and field data. Using DLR's TanDEM-X InSAR data, we validate the approach over a well-studied Brazilian tropical forest with both field inventory and lidar data. As validated against lidar data, the estimated underlying topography has an accuracy of 3 m, while the forest mean height and canopy top height have an accuracy of 3 m and 4–5 m, respectively, at the resolution of one hectare forest stands. Given the global data availability of TanDEM-X and the future TanDEM-L, this approach has the potential of wall-to-wall mapping of the forest height as well as underlying topography using single polarization/baseline.