Forest Biomass Mapping Using Continuous InSAR and Discrete Waveform Lidar Measurements: A TanDEM-X/GEDI Test Study

This article addresses the implementation of an above ground biomass (AGB) estimation scheme relying on the height-to-biomass allometry at stand level in the context of the synergistic use of continuous TanDEM-X (bistatic) interferometric synthetic aperture radar acquisitions and spatial discrete GEDI waveform lidar measurements. The estimation of forest height and horizontal forest structure from TanDEM-X data in the absence of a digital terrain model (DTM) is discussed. The possibility of estimating (top) canopy height variations independent of topographic height variations is discussed using wavelet-based scale analysis. This understanding is then exploited to define a structure index expressing the (top) canopy-only height variations in the absence of a DTM. The potential of using the derived structure information to account for the spatial variability of height-to-biomass allometry derived from the GEDI measurements is addressed. The performance of the conventional height-to-biomass allometry and the one achieved by the locally adapted implementation are compared against reference lidar measurements and discussed. The analysis is carried out using GEDI and TanDEM-X interferometric measurements and validated by using LVIS lidar measurements over the Lopé National Park, a diverse tropical forest test site in Gabon.