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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.

The retroreflective-enhanced system combines PSP/TSP with specially treated glass microspheres to enable simultaneous surface and flow field measurements. The process involves a multi-layer coating system including primer, epoxy base coat, and acrylic polymer/ceramic binder, with microspheres applied while the binder retains adhesive properties. The glass microspheres may be uncoated, half-coated with aluminum, or pre-processed to be coated in another chemical. The system leverages dual optical characteristics: the underlying PSP/TSP responds to pressure and temperature changes through luminescence intensity variations at specific wavelengths, while embedded microspheres provide retroreflective properties enabling focused SAFS, shadowgraph, or BOS visualization techniques. This configuration allows simultaneous capture of on-body surface measurements and off-body flow field disturbances. The invention enables measurements from a single viewing orientation rather than requiring orthogonal optical access points. While specific excitation lighting, wavelength filtering, and camera positioning are still necessary, the system significantly streamlines experimental setup compared to traditional separate approaches. While initially developed for aerodynamic testing and flow visualization research, this invention supports optical measurement and surface analysis applications. By enabling simultaneous measurements from a single optical access point, the retroreflective-enhanced PSP/TSP offers a streamlined solution for systems where optical access limitations are critical. The system is a TRL 6, having undergone successful validation in wind tunnel testing, and is available for patent licensing.