Event-guided dual-tracer strategy for reliable particle matching in particle-based velocimetry

Reliable particle matching in densely seeded flows with large displacements and strong velocity gradients remains a fundamental challenge in particle-based velocimetry. To address this problem, we propose an event-guided dual-tracer strategy to assist frame-based particle matching. A frame camera records the full tracer field, while an event camera continuously tracks only the sparse fluorescent tracers mixed into the main tracer population; their timestamped trajectories provide initial anchors, i.e., direct particle correspondences between the two frame images. An iterative anchor-expansion algorithm then uses these event-guided anchors as local motion references to grow additional well-supported anchors while leaving ambiguous candidates unmatched. Synthetic tests demonstrate a mean expansion precision consistently above 99% across the tested conditions. In a round-jet experiment, 334 event-guided anchors were expanded into 4964 additional accepted pairs. This strategy offers a practical route for using event sensing as a selective correspondence guide, enabling well-supported spatiotemporal particle matching in frame-based particle images while confining the event-camera bandwidth requirement only to the sparse fluorescent subset.