Three-dimensional particle tracking velocimetry and size estimation using stereo schlieren systems

Stereo single-lens focused shadowgraphy is utilized as an optical diagnostics technique for visualizing two-dimensional projections of high-velocity and explosively-launched material fragments in non-parallel light in stereo high-speed cameras. Centroids of the fragment projections in each frame of a high-speed video sequence are extracted via digital image processing techniques including image segmentation. Fragments tumbling on multiple axes of three-dimensional space result in noisy position measurements. Kalman filter-based tracking is implemented in each stereo camera view to generate an optimal estimate of the object's velocities and trajectory in the presence of noise by recursively updating position predictions with centroid position measurements. The trajectories of the fragments are reconstructed in three-dimensional space via triangulation of the 2D trajectory in each stereo camera at each frame. Size estimation is determined via the spherical assumption of the projected size of fragments and the pixel area conversion to an equivalent diameter for each fragment.