Abstract: The PIV/PTV two-phase flow measurement is employed to study the “brownout” two-phase flow induced by a near-ground hovering helicopter rotor. The deflection of the rotor tip vortex trajectory and the merging progress of vortex pairs are characterized through Γ₂ vortex core identification and modal decomposition. POD results reveal the spatial distribution and frequency characteristics of dominant modes in different wake field regions. The instantaneous particle distributions exhibit wave-like pattern excited by the wake field. Large quantities of particles are identified in the near region of x/R = 2 – 3. Correlation analysis of POD mode coefficients indicates a close relationship between particle entrainment in this region and the transport of large-scale flow structures formed in the wake field.