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NASA’s LED-ID PTV system illuminates a seeded flow with an LED rather than a laser. Instead of using double-pulsed laser flashes to capture two separate images of particle positions, the system relies on the inherent intensity decay of an LED pulse to encode velocity information directly into a single long-exposure image. The LED’s light intensity decreases over time due to capacitor discharge characteristics of the driving circuit. This controlled decay serves as a built-in intensity marker, allowing for precise determination of particle velocity and directionality without requiring an actively modulated light source. In a single-color configuration, a monochrome camera captures a long- exposure image of particle streaks as they move through the illuminated region. Because the light intensity is continuously decreasing, the recorded streaks naturally encode velocity information based on their brightness gradient. Faster-moving particles create longer streaks, while slower particles form shorter ones. The intensity variation across the streak provides additional data about directionality, enabling flow field analysis with a minimal hardware setup. For more complex flow analysis, a two-color configuration can be employed to track three- dimensional motion. In this setup, two LEDs of different colors are positioned adjacent to each other to create overlapping light sheets. A color camera, or two monochrome cameras with a dichroic mirror, captures the streaks of particles as they move between these sheets. The color transition within a particle’s streak indicates its movement between the planes of illumination, allowing users to resolve out-of- plane velocity components. Image processing techniques (e.g., advanced algorithms, high-pass filtering methods, sub-interval streak segmentation) further enhance the system's accuracy. NASA’s LED-ID PTV system has been prototyped and demonstrated with excellent results, and is available for patent licensing to industry.