Speaker
Description
The availability of multiple Synthetic Aperture radar (SAR) acquisitions separated by different spatial baselines allows to form an imaging aperture in the elevation direction and therefore to estimate a vertical profile of the backscattered power (or reflectivity). This kind of profile depends on the radar frequency and polarization, the acquisition geometry, the 3-D distribution of the scatterers in space, and their dielectric properties. In particular, different frequencies provide imaging sensitivity to different physical forest structure components. Lower frequencies (P- and L-band) penetrate through and interact with vegetation elements from the canopy top down to the ground, and they have been demonstrated to be able to fully characterize 3-D structure and to distinguish between different structure types. The sensitivity to smaller vegetation elements, which are still relevant from an ecological point of view, increases with increasing frequencies (S-, C-, X-band), but at the same time the penetration is reduced. However, recent experiments for instance with TanDEM-X data have demonstrated that the limited penetration capability becomes actually an advantage for instance for characterizing structural canopy heterogeneity in the horizontal direction.
The characterization of the information content of the different frequencies in terms of physical structure is in a very early stage of development, and becomes of particular relevance to future planned and under study SAR missions, e.g. BIOMASS (ESA), NISAR (NASA), Tandem-L (DLR). Thus, the characterization of synergies and complementarities among observations at different frequencies is crucial not only for a unified generation of biophysical products, but also for the definition of observation strategies. In this work, vertical reflectivity profiles estimated at different frequencies (from P- up to X-band) are compared, and a first assessment of the contribution of each of them in distinguishing different forest structure types is carried out. For this, structure indices derived from the radar reflectivity profiles are compared against each other as well as against plot-derived indices. Experimental results will be presented, obtained by processing real airborne (DLR F-SAR platform) acquired over temperate and tropical forests.
