Quasi-objective coherent structure diagnostics from single trajectories (vol 31, 043131, 2021)

Summary: In this study, measures of local material stretching and rotation are derived that can be computed from individual trajectories without relying on other trajectories or an underlying velocity field. These measures are quasi-objective, approximating objective coherence diagnostics in specific frames. The condition of trajectory accelerations dominating angular acceleration induced by mean vorticity is highlighted, and examples demonstrate how quasi-objective coherence diagnostics can reveal Lagrangian coherent structures even from sparse trajectory data.