Improving TanDEM-X / GEDI Tropical Forest Height Mapping with Structure Information

Abstract:
The combination of TanDEM-X interferometric coherences with the GEDI lidar full waveform measurements can provide continuous high-resolution forest height maps at large scale with sufficient accuracy without using any information about the terrain topography. In this, the lidar full waveforms provide an approximation of the X-band vertical reflectivity function to be used in the height inversion of an entire TanDEM-X scene. However, the X-band limited penetration in denser forests stands, together with the possible inadequacy of using a single profile to cover stands with very different structure characteristics, may bias significantly the height estimates. In this paper, a methodology for compensating this bias based on a structure index is presented. The structure index is a proxy to forest (stand) density, and is derived from the (high resolution) TanDEM-X phase center heights without the need of terrain topography information. The proposed methodology was applied to more than 900 TanDEM-X scenes and 2.8 millions GEDI waveforms over the tropical forests of Gabon.