A Novel RCS Imaging Measurement Method Using Airborne SAR With CAC-RMA and Calibration

Current research on airborne synthetic aperture radar (SAR) predominantly focuses on image focusing quality and radiometric calibration of pixel intensity, while limited attention has been given to the radar cross section (RCS) measurement of the targets. In this paper, we propose a methodological framework for absolute RCS imaging measurement using an airborne SAR system. First, a constant amplitude constrained Range Migration Algorithm (CAC-RMA) is introduced for SAR imaging. It preserves the signal amplitude throughout the image focusing process. Based on CAC-RMA, we establish an amplitude and coordinate mapping among radar echoes, the target’s complex image slice, and the spatial frequency domain response. It guarantees the one-to-one correspondence during imaging and in subsequent RCS measurement. Furthermore, based on the radar range equation, we formulate a theoretical framework for angle-dependent RCS measurement and absolute calibration. Numerical validations demonstrate the efficiency of the proposed method in two phases: (1) Simulated scenarios with single/multi-point targets verify the feasibility of CAC-RMA and the proposed mapping relationships between radar echoes and the spatial frequency domain response of the image slice. (2) A calibration campaign under controlled scenarios utilizing trihedral corner reflectors is designed to establish absolute calibration coefficients through scenario equivalence. Subsequent RCS measurements of three groups of reflectors and an SLICY target demonstrated the average error of 2.5 dBsm when compared to ground truth.