High-precision, robust, and rapid three-dimensional (3D) passive positioning of the radiation source is critical for modern reconnaissance systems. While synthetic aperture technology has advanced 2D passive positioning performance, existing methods fail to achieve full 3D positioning with sufficient accuracy and computational efficiency. This is because of the inherent limitations of the single-station platform in resolving elevation-angle ambiguity. To address this gap, we propose a Cross-Track Interferometric Synthetic Aperture (CISA) 3D passive positioning algorithm. The algorithm innovatively realizes robust elevation-angle measurement by recursively deriving the long baseline unambiguous phase difference step-by-step from a virtual short baseline. The 3D positioning is achieved by combining passive synthetic aperture and interferometric angle measurement. Furthermore, we establish the incoherence model of synthetic aperture passive positioning for the first time and propose a compensation method based on static acquisition data to improve the practicability of CISA. Simulation and experimental results demonstrate that the proposed CISA algorithm achieves a positioning accuracy of 4.73‰R, improves computational efficiency by 1–2 orders of magnitude compared to conventional methods, and exhibits superior robustness to noise. The research can provide a reference for the method research and engineering realization of synthetic aperture 3D passive positioning.

With the increasing demand for marine biosensing and water–air collaborative rescue in national production and life, establishing a robust cross-medium communication link has become one of the hotspots. Among them, microwave acoustic cross-medium uplink communication technology has been widely studied for its advantages of being able to be used all day and in all weather, there being no need for relay, and having high concealment. The principle is to extract the frequency of the acoustic water surface waves from the phase history of the radar echoes. However, wave interference can cause discontinuity of the phase history, resulting in difficulty in extracting the acoustic water surface waves and an increase in bit error rate (BER). This article analyses the reasons for the discontinuity of phase history and innovatively proposes a method for extracting acoustic water surface waves based on phase compensation. The discontinuity points of the phase history are compensated based on whether the range bin changes. Then, low-frequency water surface fluctuations and discontinuity points are filtered out through second-order differential joint outlier removal, which can effectively reduce the influence of phase history discontinuity on time–frequency analysis and communication decoding. The effectiveness of the proposed method was verified through simulations and experiments. The experimental results indicate that the BER of the proposed method is 25% of that of the Wavelet–Kalman Filtering method. The proposed method provides a new approach for microwave acoustic cross-medium uplink communication.