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 wire. As the electrical resistance of most metals is dependent upon the temperature of the metal (tungsten is a popular choice for hot-wires), a relationship can be obtained between the resistance of the wire and the flow speed. Several ways of implementing this exist, and hot-wire devices can be further classified as CCA (constant current anemometer), CVA (constant voltage anemometer) and CTA (constant-temperature anemometer). The voltage output from these anemometers is thus the result of some sort of circuit within the device trying to maintain the specific variable (current, voltage or temperature) constant, following Ohm's law. Additionally, PWM (pulse-width modulation)