Particle Dynamics Analysis (PDA) is an extension of the LDA technique. Where in LDA the probe has it's own deteching optics, in PDA the probe contains only transmitting optics (the laser). Separate from the probe, a lens is focused on the laser interference area. Behind the lens is an array of optical sensors that measure the particle dynamics.
PDA's specific strengths are the ability measure a range of particles from sub-micron to several millimeters, up to supersonic speeds, multi-component velocity information and no calibration. It seems the technique is most often used with spherical particles, and this may be a limitation of the method. Dantec Dynamics has compiled a concise technological overview brochure.