Interference fading suppression in Φ-OTDR using space-time-frequency joint processing

Phase-demodulation-based phase-sensitive optical time domain reflectometry (Φ-OTDR) is widely used for the quantitative retrieval of distributed perturbations. However, the inherent interference fading in Φ-OTDR degrades the signal-to-noise ratio (SNR) and phase-demodulation accuracy, thereby limiting sensing performance. Although various digital signal processing methods have been proposed to address this issue without modifying the system hardware, most of them operate in a single domain, and only a few exploit the multidimensional characteristics of the sensing signals. In this work, a novel space-time-frequency (STF) joint processing method is proposed for effective interference fading suppression in a single-pulse coherent Φ-OTDR system. The received Rayleigh backscattered signals are processed jointly in the spatial, temporal, and frequency domains using spatial differential operation, temporal Fourier transformation, and a robust two-dimensional adaptive weighting strategy constructed from spectral characteristics and spatial correlation. Experimental results show that the proposed method corrects false phases caused by fading and reduces amplitude fluctuations from more than 40 dB to approximately 20 dB. Compared with the conventional moving rotated-vector-average (MRVA) method, the proposed STF method improves the average SNR by ∼16.6 dB and the phase-demodulation accuracy by ∼14.7 dB, while faithfully recovering the applied vibrations without waveform distortion. The proposed method provides an effective digital-domain solution for interference fading suppression in Φ-OTDR.