  High-speed stereo PIV-measurements have been performed in a turbulent
boundary layer at Re$_{\theta}$ of 9800 in order to elucidate the coherent
structures. Snapshot proper orthogonal decomposition (POD) and dynamic mode
decomposition (DMD) are used to visualize the flow structure depending on the
turbulent kinetic energy and frequency content. The first six POD and DMD modes
show the largest and the lowest amount of energy and frequency, respectively.
Lagrangian coherent structure (LCS) based on the algorithm developed using the
variational theory is also applied to track the flow via attracting and
repelling trajectories. The shapes and the length of the trajectories show
variation with increasing advection time. LCS trajectories are overlayed with
the individual POD and DMD modes. Repelling and attracting lines cover the
structure of these modes. Reconstructed flow fields from individual POD modes
are also used to generate new LCS trajectories. The energy and frequency
content have a direct impact on the length of the trajectories, where the
longest reconstructed trajectories associate with the higher energy and lower
frequency modes, and vise verse. The multiple intersection points between the
repelling and attracting lines marked the low momentum regions.
