  Direct estimation of Lagrangian turbulence statistics is essential for the
proper modeling of dispersion and transport in highly obstructed canopy flows.
However, Lagrangian flow measurements demand very high rates of data
acquisition, resulting in bottlenecks that prevented the estimation of
Lagrangian statistics in canopy flows hitherto. We report on a new extension to
the 3D Particle Tracking Velocimetry (3D-PTV) method, featuring real-time
particle segmentation that outputs centroids and sizes of tracer particles and
performed on dedicated hardware during high-speed digital video acquisition
from multiple cameras. The proposed extension results in four orders of
magnitude reduction in data transfer rate that enables to perform substantially
longer experimental runs, facilitating measurements of convergent statistics.
The extended method is demonstrated through an experimental wind tunnel
investigation of the Lagrangian statistics in a heterogeneous canopy flow. We
observe that acceleration statistics are affected by the mean shear at the top
of the canopy layer and that Lagrangian particle dispersion at small scales is
dominated by turbulence in the wake of the roughness elements. This approach
enables to overcome major shortcomings from Eulerian-based measurements which
rely on assumptions such as the Taylor's frozen turbulence hypothesis, which is
known to fail in highly turbulent flows.
