P band penetration in tropical and boreal forests: Tomographical results

In this paper we discuss some relevant features observed concerning wave penetration at P-band in boreal and tropical forests. The discussion will be based on results obtained from the multi-polarimetric and multi-baseline data-sets relative to the forest sites within the Krycklan river catchment, Sweden, and the area of Paracou in French Guyana, collected in the frame of the ESA campaign BioSAR 2008 and TropiSAR 2009, respectively. The analysis is carried out by exploiting the SAR tomography technique, which allows to separate backscattering contributions from different heights within the vegetation layer. One first relevant result is relative to the difference between the vertical distribution of the backscattered power in the two investigated test sites. In the boreal forest site the most relevant scattering contributions are observed at the ground level, not only in copolarized channels but also in HV, whereas in the tropical forest the presence of scattering from the ground is poorer and the vegetation volume is well visible. Most relevant features of the investigated tropical forest site are those relative to the dependency of the vertical backscattering distribution with respect to topographic slope and forest biomass. In particular, the innermost forest layer is observed to be substantially invariant to topographic slopes, whereas the backscattered power at 30 m above the ground is observed to yield the best connection with forest biomass, resulting, in this case, in a correlation factor of 0.82 with respect to in-situ measurements at 125 m spatial resolution.