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The Ground-Based SAR Dynamic Measurement System is capable of acquiring the time-displacement sequence of ancient pagodas, enabling effective assessment of their structural health. To extract the instantaneous resonance frequency of the pagodas from signals containing noise, the conventional Hilbert-Huang Transform often encounters mode mixing issues, leading to the influence of false components on the measurement accuracy. Therefore, this study employs a non-interference method based on normal time-frequency transform Theory to monitor the pagodas.The essence of the normal time-frequency transform Theory lies in a kind of linear filter, which exhibits strong anti-interference capability in extracting periodic signal components. This approach yields time-varying, unbiased harmonic instantaneous amplitude, frequency, and phase. The monitoring and analysis of the ground-based SAR dynamic detection signals from the Rangdeng Pagoda in Tongzhou District, Beijing, were conducted in this study. Experimental results indicate that the amplitude and frequency derived from the normal time-frequency transform Theory better match the actual vibration characteristics of the pagoda. Additionally, this method involves lower computational complexity compared to conventional approaches and places greater emphasis on continuous time-frequency analysis. These findings provide scientifically reasonable foundational data for analyzing the architectural characteristics and safety assessment of ancient pagodas.
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