Book excerpt: The average rate at which the radar signal crosses a voltage level is linearly dependent on the root mean square of the turbulent wind component in the direction of the beam (1, 2), and therefore constitutes an anemometer with these characteristics. All tracers within the illuminated volume contribute to the signal. This anemometer therefore senses an average over the space they occupy which is at most equivalent to a cylinder standing half a pulse length high and straddling a diameter equal to the product of the range and beamwidth.