Refined ship interpretation in compact polarimetric SAR via formalism and joint feature space construction

The two-channel cost of Compact Polarimetric (CP) Synthetic Aperture Radar (SAR) with close performance compared to four-channel Full Polarimetric (FP) SAR, has great potential for observing and interpreting ship targets. In the existing literature of ship targets using CP SAR data, the ships are often studied as a whole target for detection purpose, and the refinement of the scattering mechanism of ships remains a challenge. CP SAR measurements depend on the transmitted wave, and there are different interpretations of the two-channel polarization ratio for the same scatterer in different CP modes. The diversity of interpretations inconveniences the use of CP data and leads to non-uniformity in target decomposition algorithms. Moreover, the existing CP target decomposition methods cannot provide a refined interpretation for the inner structure of ships. In response to the above issues, this study formalizes CP data, constructs a joint feature space, and applies iterative clustering to achieve refined ship interpretation in this paper. First, we propose a novel polarimetric formalism method that establishes a unified CP covariance matrix, ensuring a consistent interpretation of scatterer physics across different CP modes. Second, we construct a discriminative joint feature space, i.e. the RCP/αBCP plane, and further introduce the surface-to-volume ratio for dynamic adaptive threshold adjustment. Finally, we use the constructed classification space for initialization and then use the Generalized Hybrid Polarimetric Scattering Similarity (GHPSS) based Wishart classifier to iteratively classify the CP ship target. Experiments were conducted using CP ship data simulated from GF-3 FP data, and the results show that the method proposed can extract the ship’s scattering mechanisms in a refined manner and preliminarily determine the ship type based on the scattering mechanism. The results support the potential of using CP data for refined ship interpretation.