Innovative methods to calculate biomass of tropical forests from TanDEM-X data

Satellites TerraSAR-X and TanDEM-X

Satellites TerraSAR-X and TanDEM-X 3D-scanning the earth surface
Image: EADS Astrium

Biotrop-X is a colaborative project between the Helmholtz Centre for Environmental Research (UFZ) and the German Aerospace Center (DLR). Its target is the development of new methods for local calculation of biomass stocks in different tropical forest areas using remote sensing systems such as TanDEM-X. The outcomes should contribute to continuous coverage mapping of above ground carbon stocks in vegetation and their dynamics. Concrete tasks are, first of all, finding relations between parameters measurable via remote sensing, e.g. the height profile of tree crowns, and intrinsic properties, like the biomass of the forest. Furthermore, it needs to be investigated whether these relationships are valid and applicable for different geographical regions and forest ecosystems, and what the accuracy of carbon balances inferred from repeated radar measurements would be.

Forest growth simulations serve as an important tool to answer these questions. With forest models like FORMIND large datasets of virtual forest inventories can be generated, which thereafter can be systematically screened for the above mentioned relationships. Found relations are validated based on measurement data from real forest inventory plots at different research sites in combination with the corresponding TanDEM-X measurements from these sites.

Rotation of Lidar point cloud

Simulated Lidar point cloud of a forest grown in FORMIND

The project is divided into the following stages: At first, information about forest height and structure are generated from TanDEM-X data. Then, different scenarios are simulated with FORMIND and resulting data will be searched for relations between the different forest characteristics. In the next step, the knowledge gained from the simulations will be transferred to the field data to make predictions about the biomass in the test areas based on radar data. Following that, it will be investigated, whether time series of radar scans allow conclusions on biomass dynamics. In the final stage, all predictions will be validated based on the inventory data and the models will be tested for their general applicability.

100 years of forest development

Canopy height model (CHM) of 25 ha of the Barro Colorado Island forest in Panama grown in FORMIND. Fires cause disturbance followed by natural succession. CHMs are derived from Lidar simulations. Radar will have lower spatial resolution than Lidar.

The anticipated result will be a model which allows deriving the biomass of an arbitrary tropical forest, independent of its geographic location or forest type, from TanDEM-X data. Subsequently, the model can be utilized for large scale mapping.

Test sites:
BCI, Panama
Loja, Ecuador

Contact: Nikolai Knapp, Rico Fischer

Funded by the German Federal Ministry for Economic Affairs and Energy