Scattering-Order-Based Decoupling Model for TWR Building Interior Structures Extraction

Building interior structure sensing using through-the-wall radar (TWR) is crucial for safety and security applications. However, existing methods struggle to decouple first-order wall reflections from second-order corner interactions, resulting in ambiguity between wall discontinuities and corner features. To address these challenges, this paper proposes a scattering-order-based decoupling model integrating geometric optics (GO) and physical optics (PO) principles to enable accurate building characterisation. Our proposed model decomposes total radar returns into distinct components including first-order scattering from walls and second-order double-bounce scattering from corners. For wall characterisation, the scattering response is derived via PO integrals, considering reflections from parallel and perpendicular orientations relative to the radar. For corner detection, a coupled GO-PO model is developed to explicitly capture double-bounce interactions between adjacent walls. This analytical formulation isolates the corner representation by excluding first-order contributions, ensuring the corner signature consists exclusively of coupled scattering energy. As a result, this approach effectively suppresses first-order wall scattering artifacts and reduces wall-induced ambiguities. Based on these analytical derivations, we designed a physics-based dictionary method to enable building interior structure extraction. Extensive simulations and experiments validate that our model improves wall and corner extraction, supporting more reliable building interior reconstruction.