CROWN COPYRIGHT / HEALTH & SAFETY LABORATORY / SCIENCE PHOTO LIBRARY CROWN COPYRIGHT / HEALTH & SAFETY LABORATORY / SCIENCE PHOTO LIBRARY
Laser velocity measurement. Technician uses beams from a laser to measure the velocity of air coming from a dummy's mouth which is simulating breathing. The 4 beams of this Laser Doppler Velocimeter (LDV) or anemometer use the Doppler effect to measure the velocity of the gas. This effect raises or lowers the frequency of light when it is scattered by fine particles moving in the air. The gas velocity can be measured by monitoring the Doppler shift. Dummies like this are used to assess people's exposure to airborne contaminants. Photograph of research done by the Health and Safety Laboratory in Britain.
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