Dual-Frequency Phase Unwrapping for 3D InISAR Imaging of Non-Cooperative Targets

The Three-Dimensional Interferometric Inverse Synthetic Aperture Radar Imaging (3D InISAR) method tackles the interpretability challenges associated with two-dimensional ISAR. It achieves this by providing a 3D representation of the target, offering a more comprehensive understanding of its shape and features. However, this approach faces challenges related to interferometric measurement ambiguity, especially in operational scenarios where factors such as target type and range of the target come into play. Conventional methods for interferogram unwrapping used in Interferometric SAR systems for topographic mapping cannot be directly applied to man-made objects in ISAR due to the discrete nature of ISAR imaging, which violates the assumption of spatial continuity. To address these issues, various multi-receiver solutions have been proposed in the literature. This paper introduces a different approach: a maximum likelihood-based dual-frequency technique applied to 3D InISAR imaging. Leveraging the frequency diversity inherent in a wideband receiver and utilizing two non-overlapping sub-bandwidths, this method effectively resolves measurement ambiguity. Testing the method in a simulated scenarios highlights the enhanced reconstruction abilities of the method and the benefits of utilizing extended physical baselines.