Abstract
Allometric relations that link forest above ground biomass to top forest (i.e. canopy) height are of particular significance in the context of lidar and interferometric Synthetic Aperture Radar (SAR) remote sensing, as both techniques allow accurate height measurements at ecologically relevant spatial scales. Besides the often unknown allometry itself, its spatial variation in heterogenous forest environments restricts the performance when using a single fixed height-to-biomass allometric relation. This paper addresses how forest structure information derived from interferometric TanDEM-X data can be used to locally adapt a known height-to-biomass allometry in heterogeneous forests, and to improve biomass estimation performance. The analysis is carried out using TanDEM-X interferometric measurements in three tropical forest test sites in Gabon. A structure index expressing forest density is derived from the TanDEM-X data. Then, a continuous relationship between the structure index and the allometric level that defines the forest height-to-biomass allometry is reconstructed from the available lidar data, and used to vary the height-to-biomass relationship. Finally, the potential of the derived structure index to support an allometric relationship common to all sites is evaluated. The experimental results show the appropriateness of TanDEM-X data for characterizing structure and in this way improving the biomass estimation performance.
Highlights
BIOMASS has a direct relationship to carbon content and is a measure of forest and ecosystem productivity
The open question is how far the knowledge of forest structure can be used to adapt the general heightto-biomass allometry to local scales. This paper addresses this question in the context of TanDEM-X and waveform lidar measurements
Reference forest height and biomass data as well as forest structure indices have been derived from airborne (LVIS) full waveform data acquired almost at the same time as the TanDEM-X data
Summary
BIOMASS has a direct relationship to carbon content and is a measure of forest and ecosystem productivity. Summarizing, two main factors limit the use of the height-tobiomass allometry in a wide context: (i) the large uncertainty in the knowledge of the allometric parameters (α0, β0) for the individual forest conditions (arising from the insufficiency or complete lack of appropriate reference measurements), and (ii) the inability to adapt (α0, β0) to the spatial variability of forests. Today both limitations appear less restrictive making a revisit of the height-to-biomass allometry attractive. The estimation of H and HS from TanDEM-X data, the performance of conventional height-to-biomass allometry and the use of HS to improve the height-to-biomass allometry performance for different tropical forest types and conditions are discussed
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