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
Haar measure nontrivial but the modular function of formula_3 is trivial. The quotient of these cannot be extended to any character of formula_3, so the quotient space formula_114 (which can be thought of as 1-dimensional real projective space) does not have even a semi-invariant measure. Using the general theory of Lebesgue integration, one can then define an integral for all Borel measurable functions formula_84 on formula_3. This integral is called the Haar integral. If formula_11 is a left Haar measure, then for any Haar integrable function formula_84 on formula_3. This is immediate for indicator functions, being essentially the definition of left invariance.