TSI PIV systems measure velocity by determining particle displacement over a precisely selected time using a double-pulsed laser technique. A laser light sheet illuminates a plane in the flow, and the positions of particles (naturally present or added to the flow to have sufficient number of tracers) in that plane are recorded using a digital camera. A short time (micro or milliseconds) later, a second pulse illuminates the same plane, creating a second set particle image.
From these sets of images, PIV analysis algorithms obtain the particle displacements for the imaged region, to give the velocity information at thousands of locations-quickly, easily, reliably. Flow properties such as vorticity and strain rates are obtained for the entire region. Mean velocity, turbulence intensity, and higher order statistics are also obtained.