Multi-receiver wide-beam SAS chirp scaling imaging algorithm based on complex dual square-root series inversion

Conventional synthetic aperture sonar (SAS) imaging algorithms are typically designed for narrow-beam conditions, and their imaging performance significantly degrades under wide-beam scenarios, which severely limits the advancement of SAS imaging technology. This paper presents a high-precision imaging algorithm based on series reversion of the dual-square-root (DSR) form. Deriving the two-dimensional (2D) spectrum is a critical step in constructing filtering and phase compensation functions. However, the complex DSR structure of the range history complicates the derivation process, and approximations of the two-way propagation time under wide-beam conditions can negatively impact imaging quality. To address these challenges, this study preserves accurate time-domain information and the DSR structure, performs a Taylor series expansion, and applies series reversion to obtain a closed-form expression of the 2D spectrum. A frequency-domain expansion in terms of azimuth and range frequencies is also derived. Based on this spectrum, matched filtering is performed in both the azimuth and range directions, resulting in well-focused, high-resolution SAS simulation images. The effectiveness of the proposed algorithm is further validated through water-tank experiments, demonstrating favorable focusing performance and extending the applicability of SAS imaging to wide-beam conditions.