To detect delamination and internal void defects within sandwich composite ma-terials, such as those used in wind turbine blades, this study employs a Remote Impact Test (RIT), analyzing the dispersion characteristics of the generated stress waves. RITs were conducted on specimens that varied in both thickness and defect type. Time-frequency spectrograms and dispersion curves were then obtained using two time-frequency analysis techniques: wavelet analysis and reassigned spectrograms (derived from Short-Time Fourier Transformation). The accuracy of defect identifica-tion is demonstrably improved through the cross-examination of the findings from these methods.