need to measure velocities inside engines or through nozzles Environmental research (combustion research, wave dynamics, coastal engineering, tidal modeling, river hydrology, etc.). One disadvantage has been that laser Doppler velocimetry sensors are range-dependent; they have to be calibrated minutely and the distances where they measure has to be precisely defined. This distance restriction has recently been at least partially overcome with a new sensor that is range independent. Automation Laser Doppler velocimetry can be useful in automation, which includes the flow examples above. It can also be used to measure the speed of solid objects, like conveyor belts. This can be useful in situations where attaching a rotary encoder (or a different mechanical speed measurement device) to the conveyor belt is impossible or impractical. Medical applications Laser Doppler velocimetry is used in hemodynamics research as a technique to partially quantify blood flow in human tissues such as skin or the eye fundus. Within the clinical environment, the technology is often referred to as laser Doppler flowmetry; when images are made, it is referred to as laser Doppler imaging. The beam from a low-power laser (usually a laser diode) penetrates the skin sufficiently to be scattered with a Doppler shift by the red blood cells and return to be concentrated on a detector. These measurements are useful to monitor the effect of exercise, drug treatments, environmental, or physical manipulations on targeted micro-sized vascular areas. The laser Doppler vibrometer is being used in clinical otology for the measurement of tympanic membrane (eardrum), malleus (hammer), and prosthesis head displacement in response to sound inputs of 80- to 100-dB sound-pressure level. It also has potential use in the operating room to perform measurements of prosthesis and stapes (stirrup) displacement. Navigation The Autonomous Landing Hazard Avoidance Technology used in NASA's Project Morpheus lunar lander to automatically find a safe landing place contains a lidar Doppler velocimeter that measures the vehicle's altitude and velocity. The AGM-129 ACM cruise missile uses laser doppler velocimeter for precise terminal guidance. Calibration and measurement Laser Doppler velocimetry is used in the analysis of vibration of MEMS devices, often to compare the performance of devices such as accelerometers-on-a-chip with their theoretical (calculated) modes of vibration. As a specific example in which the unique features of Laser Doppler velocimetry are important, the measurement of velocity of a MEMS watt balance device has allowed greater accuracy in the measurement of small forces than