Accounting for Co-Registration Errors in the Interferometric Coherence Model of Semi-Transparent Media

Across-track synthetic aperture radar (SAR) interferometry is a well-established technique to obtain the topographic information using a pair of SAR images, whose coherence influences the topographic height accuracy. Volume decorrelation occurs in the presence of semi-transparent media, such as forests and vegetation, and is usually modeled using the vertical scattering profile, thus providing a link between the coherence and the physical parameters of the medium. This has been successfully exploited in polarimetric SAR interferometry and SAR tomography to retrieve 3-D structure information of the scene. Future SAR systems are expected to be equipped with larger bandwidths, which also allow for interferometric acquisitions with larger baselines and enhanced height accuracies. In these cases, a significant amount of co-registration decorrelation may occur within the volume, which should be considered in the model of volume decorrelation. This letter presents a novel volume decorrelation model, which accounts for co-registration effects and accurately predicts the coherence for interferometric acquisitions with large bandwidths and/or baselines. Simulation examples are shown for typical scenarios to prove the validity of the model, which is capable of predicting the phase of the complex coherence of a semi-transparent medium with subdegree accuracy. The proposed model will be a crucial tool to analyze semi-transparent media in future spaceborne SAR missions and drone-borne SAR systems.