Inertial particles advected by a background flow can show complex structures . We consider inertial particles in a 2D Taylor-Green (TG) flow and characterize particle dynamics as a function of the particle's Stokes number using dynamic mode decomposition (DMD) method from particle image velocimetry (PIV) like-data . We observe the formation of caustic structures and analyze them using DMD to (a) determine the Stokes number of the particles, and (b) estimate the particle Stokes number composition . Our analysis in this idealized flow will provide useful insight to analyze inertial particles in more complex or turbulent flows . We propose that the DMD technique can be used to perform a similar analysis on an experimental system.