  Particle tracking in turbulent flows is fundamental to the study of the
transport of tracers, inertial particles or even active objects in space and
time, i.e. the Lagrangian frame of reference. It provides experimental tests of
theoretical predictions (e.g. for the statistics of fluid accelerations and
particle dispersion) and helps to understand important natural processes where
particle inertia is important (e.g. cloud microphysics). While the spatial
(Eulerian) properties of turbulent flows have been studied for high,
atmospheric Reynolds numbers ($R_\lambda > 10^4$), the profound difficulties in
accurately tracking particles in turbulent flows have limited the Reynolds
numbers in the Lagrangian reference frame to the Taylor scale Reynolds numbers
$R_\lambda \lesssim 10^3$. Here we describe a setup that allowed Lagrangian
particle tracking at $R_\lambda$ between 100 and 6000 in the Max Planck
Variable Density Turbulence Tunnel (VDTT). We describe the imaging setup within
the pressurised facility, the laser illumination, the particles and the
particle dispersion mechanism. We verify that the KOBO Cellulobeads D-10
particles are suitable tracers. They carry negligible charge and their Stokes
number is small over the full range of experimental conditions. We present
typical data from the experiment and discuss the challenges and constraints of
the setup.
