previously possible, through directly measuring the ratio of this velocity to the speed of light. This is a fundamental, traceable measurement that now allows traceability of small forces to the S.I. System. See also Hot-wire anemometry Laser Doppler imaging Laser Doppler vibrometer Laser surface velocimeter Molecular tagging velocimetry Particle image velocimetry Particle tracking velocimetry Photon Doppler velocimetry Velocity interferometer system for any reflector (VISAR) References External links LDA/LDV principle LDV overview Basic Principles of Velocimetry Laser Surface Velocimetry Video Laser applications Doppler effects Measurement Transport phenomena