The traditional pulse repetition interval (PRI) transform method and modified PRI transform method have a low ability to recognise the complex PRI modulation type adopted in spaceborne synthetic aperture radar systems. To solve this problem, a short-time modified PRI transform (STMPT) method based on the traditional PRI transform method was proposed. The STMPT method converts the one-dimensional representation of PRI estimation results into a time-varying characteristic sensitive (TVCS) matrix of the PRI. Combined with the mathematical models of the four PRI modulation types including PRI fixed, staggered PRI, fast PRI change, and a more elaborated PRI sequence concatenating multiple fast PRI change sequences, the nonzero segment characteristics were obtained by incoherent accumulation and rearrangement of the TVCS matrix. Parameter estimation of the four PRI modulation types was also realised based on the geometrical and statistical characteristics. Finally, the effectiveness and performance of the algorithm were verified by simulation analysis.

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