FluxNet the gas in question. This mass flux makes the FluxNet project a valuable tool to scientists trying to monitor long term changes in trace gas flux within the atmosphere. Many different forms of anemometer exist on the current market. Unfortunately, the majority of the anemometers can only measure wind velocity in one plane and require a certain start-up wind speed. Sonic anemometers are solid state devices that measure the wind speed by passing ultrasonic sound waves through the moving air. As wind speed changes, so does the air density and when the density changes, so does the speed of sound.
Anemometer anemometers are also used, wherein the velocity is inferred by the time length of a repeating pulse of current that brings the wire up to a specified resistance and then stops until a threshold "floor" is reached, at which time the pulse is sent again. Hot-wire anemometers, while extremely delicate, have extremely high frequency-response and fine spatial resolution compared to other measurement methods, and as such are almost universally employed for the detailed study of turbulent flows, or any flow in which rapid velocity fluctuations are of interest. An industrial version of the fine-wire anemometer is the thermal flow meter,