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Techniques based on coherent combination of complex (amplitude and phase) SAR data, in particular Pol-InSAR and 3D multibaseline SAR Tomography (Tomo-SAR), can extract rich information on complex scenarios with multiple scatterers mapped in the SAR cell. However, forest scenarios are characterized by a temporal decorrelating volume canopy scatterer, and a set of related open problems exists, in particular for Tomo-SAR techniques to be applied to space monitoring of biomass. Multipass/multibaseline 4D Differential Tomography (Diff-Tomo) is a promising advancement in this field, furnishing space-time signatures of multiple scatterer dynamics in the SAR cell, in particular with urban applications. In this paper, to deal with the forest decorrelation issues in Tomo-SAR, experimental advances are presented of the original extension of Diff-Tomo methods for analyzing vegetated scenes, to extract jointly geometric and dynamic information of forest layers. The Diff-Tomo enabled functionalities are separation in the height dimension of different temporal coherence levels that are mixed (undiscriminated) in classical total coherence analyses ("Tomography of coherences"), and 3D Tomography robust to temporal decorrelation. Extended airborne P-band multipolarimetric results and phenomenological investigations are shown.

Multibaseline (MB) SAR tomographic (3D) elevation beamforming, i.e. spatial spectral estimation, is a promising technique in the growing field of advanced interferometric SAR methods for sensing complex scenarios with multiple (layover or volumetric) scatterers mapped in the SAR cell. Recently, the Tomo concept has been integrated with the differential interferometry concept, producing the new "differential tomography" (Diff-Tomo, "4D") processing mode. Advances in the experiments of these new frameworks are presented for complex multiple scattering scenarios, also with temporal signal variations, both from scatterer deformation motions and temporal decorrelation. Results are reported of Tomo/Diff-Tomo single-look superresolution and light-burden processing in urban areas, with the new generation high-resolution COSMOSkyMed data. Moreover, new results are shown concerning the innovative capability of Diff-Tomo of analyzing volumetric forest scenarios, based on the original concept of the "space-time" signatures of temporal decorrelation. E-SAR P-band analyses are reported about separation of the canopy and ground temporal decorrelation mechanisms.

3D SAR Tomography exploiting multibaseline data is an important evolution of SAR Interferometry, to sense complex scenarios with multiple scatterers mapped in the SAR cell. This concept has been also integrated with multipass Differential Interferometry, producing the Differential Tomography (Diff-Tomo, "4D") mode which furnishes "space-time" signatures of multiple (layover) dynamic scatterers. Diff-Tomo allows the joint resolution of multiple heights and deformation velocities of the scatterers mapped in a SAR pixel, i.e. 4-D (Multidimensional) SAR imaging, with applications e.g. in the monitoring of subsidences of complex urban areas and infrastructures. Moreover, Diff-Tomo has been also conceived in higher order version ("5D"), to extract information of layover nonuniform deformating scatterers, including the case of thermal dilations. In this paper, recent UniPI/RaSS Multidimensional Diff-Tomo work is extended, presenting latest 4D/5D algorithm advances and related first extensive trials with COSMO-SkyMed data. In particular, a new 5D single-look Diff-Tomo processor with superresolution capability and light computational burden for seasonal thermal dilation in layover zones is treated.

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