Forest structure from longer wavelength SARS

In this paper we address three topics related to SAR Tomography of forest scenarios at P-Band. In first place we discuss the role of pulse bandwidth, which is shown to play a critical role as for the capability of the Tomographic system to separate ground and canopy contributions. Accordingly, vertical resolution depends not only on baseline aperture, but also on pulse bandwidth. Another factor to be accounted for is phase calibration, as the quality of the vertical focusing carried out by SAR Tomography is strictly related to the condition that phase contributions due to platform motion or atmospheric propagation are properly compensated for. Finally, multiple scattering phenomena are likely to occur at longer wavelengths, resulting in Tomographic techniques not being suffice for the aim of discriminating ground and volume scattering. The three points above are here discussed in light of the results achieved in the framework of the ESA campaign BioSAR 2008. The analysis has been carried out by exploiting the Algebraic Synthesis technique, which provides a theoretical framework to decompose the SAR signal into ground-only and volume-only contributions. Ground-only contributions provide an easy and viable way to phase calibrate the data stack. Volume-only contributions, if correctly identified, allow a direct Tomographic imaging of the vegetation layer. The impact of pulse bandwidth is tackled by assuming a Common Band Filtering approach, which results in a vertical resolution improvement by a factor 2.