Anemometer turbines usually requires a refresh rate of wind speed measurements of 3 Hz, easily achieved by sonic anemometers. Three-dimensional sonic anemometers are widely used to measure gas emissions and ecosystem fluxes using the eddy covariance method when used with fast-response infrared gas analyzers or laser-based analyzers. Two-dimensional wind sensors are of two types: Acoustic resonance anemometers are a more recent variant of sonic anemometer. The technology was invented by Dr Savvas Kapartis and patented in 2000. Whereas conventional sonic anemometers rely on time of flight measurement, acoustic resonance sensors use resonating acoustic (ultrasonic) waves within a small purpose-built cavity in
Cylinder set measure "γ" is the standard Gaussian measure on R. The canonical Gaussian cylinder set measure on an infinite-dimensional separable Hilbert space "H" does not correspond to a true measure on "H". The proof is quite simple: the ball of radius "r" (and center 0) has measure at most equal to that of the ball of radius "r" in an "n"-dimensional Hilbert space, and this tends to 0 as "n" tends to infinity. So the ball of radius "r" has measure 0; as the Hilbert space is a countable union of such balls it also has measure 0, which is a contradiction.