US Patent 7703319 Characterization of aircraft wake vortices

A bi-static sodar system and method are used to measure and monitor the wake vortices of aircraft in the flight path of an airport runway. A loudspeaker (16) is arranged on one side of the flight path (12) and transmits a series of acoustic pulses to illuminate portion of the flight path. Multiple microphones (18, 20 and 22) are arranged on the opposite side of the flight path (12) so as to receive direct signals from the loudspeaker (16) and forward-scattered echo signals from an echo source (26) within the illuminated portion of the flight path. The microphones (18, 20 and 22) are arranged at different distances from the loudspeaker so that the time intervals between the receipt of the direct and echo signals from each pulse will vary because of the different locations of the microphones. This variation is used to assist in identifying the location and other characteristics of the echo signals and in generating an output indicative of a wake vortex (28).