Impact of Dielectric Changes of Forest Volumes on L-Band SAR Reflectivity Profiles

Abstract

Synthetic Aperture Radar (SAR) Tomography (TomoSAR) allows reconstructing a vertical profile of the power backscattered by natural volumes by combining more than two SAR images acquired with slightly different incidence angles. Being an electromagnetic quantity, the profile depends on the radar frequency, polarization, and acquisition geometry, but also on the 3-D distribution of the backscattering elements and their dielectric properties. The characterization of each one of these factors is crucial to enable the extraction of physical 3-D structure attributes from TomoSAR profiles. The objective of this work is to investigate how L-band TomoSAR reflectivity profiles of forest volumes are affected by seasonal and weather-induced changes of their dielectric properties. Radiometric (e.g. ground and volume powers) and geometric (e.g. center of mass of the volume-only profiles and phase centers of the volume scattering layers) parameters have been estimated under different conditions and compared. Then, TomoSAR data sets affected by dielectric non-stationarities (i.e. changing conditions) have been considered in order to assess the invariance of each radiometric and geometric parameter. This analysis has been carried out by processing four L-band airborne TomoSAR data sets acquired before and after a rainfall, and in spring and autumn over the Traunstein forest (South of Germany).