Abstract: A monostatic sodar system (10) for atmospheric sounding includes a processor and display unit (12) that generates a set of acoustic chirps for transmission by transmitter 20. Discontinuities (22, 24 and 26) result in echoes (28, 30 and 32) being returned to a receiver (38) of system (10). Receiver (38) outputs extracted echo signals on line to the processor (12) for analysis. Detector (36) implements a Fourier domain matched-filter to extract echo signals from noise. By using a set of multiple chirps of increasing length with increasing intervals between them, substantially any feasible range can be accommodated using send-then-listen techniques with the benefit of high s/n performance.

Abstract: 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).

Abstract: 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).

Abstract: A monostatic sodar system (10) for atmospheric sounding includes a processor and display unit (12) that generates a set of acoustic chirps for transmission by transmitter 20. Discontinuities (22, 24 and 26) result in echoes (28, 30 and 32) being returned to a receiver (38) of system (10). Receiver (38) outputs extracted echo signals on line to the processor (12) for analysis. Detector (36) implements a Fourier domain matched-filter to extract echo signals from noise. By using a set of multiple chirps of increasing length with increasing intervals between them, substantially any feasible range can be accommodated using send-then-listen techniques with the benefit of high s/n performance.

Abstract: Sodar systems and methods for acoustically sounding air are disclosed in which chirps longer than 300 ms—and preferably with durations of tens of seconds—are used along with matched filter and/or Fourier processing methods to derive phase signals indicative of air characteristics in range. A listen-while-transmit strategy is preferred, the direct signal being removed by subtracting the phase signals from two or more receivers located near the transmitter so as to be in the same noise environment. The resultant differential signals can be related to cross-range wind with range distance. In one example, apparatus (100) is employed comprising a reflector dish (102) over which one central loudspeaker (110) and four microphones (112, 114, 130 and 132) are mounted, the microphones preferably being located on cardinal compass points and having their axes (124, 126) slightly angled with respect to the vertical transmission axis (122).

Abstract: Two SODAR systems (12a and 12r) for detecting and characterizing vortices (16) shed from landing or departing aircraft (14) as at an airport (10) are positioned so that one, the active system (12a) is located beneath the likely vortices (16) and the other, the reference system (12r) is located away from the vortices but in the same ambient environment. Thus, where a wind duct or thermal inversion (18) is present, both SODAR systems will detect echoes (22 and 28) generated thereby, whereas only the active system (12a) will detect echoes (24) from wake vortices (16). By differencing the outputs of the reference and active systems, better vortex identification and discrimination is achieved. Only one SODAR system need be used where sufficiently normal conditions prevail between aircraft activity, since readings taken in the absence of aircraft can be used as reference data for subtraction from ‘active’ data recorded during the presence of aircraft.

Abstract: A method and system for acoustically sounding the lower atmosphere involves the transmitting of an acoustic chirp and the processing of returned echoes and interference using wavelet and matched filter techniques. A single transmitter and four receivers may be used, with receivers located equidistant from the transmitter on the cardinal points of the compass. N, S, E, & W inputs are digitized and input to a wavelet filter (50) together with the transmitter chip signal (R or D) for the attenuation of the direct signal and ambient noise signals. The interference-attenuated signals are then processed in a matched filter (52) to extract phase and amplitude outputs (54 and 56), the phase output being unwrapped (70). The N and S phase signals and the E and W phase signals are then separately differenced (74 and 80) and the results used to compute (86 and 92) wind speed and bearing.

Abstract: Methods and apparatus for atmospheric sounding using acoustic chirps are disclosed, the transmitted and echo chirps being compared in a mixer that yields frequency sums and differences. Preferably, the mixing is performed as a complex multiplication in the Fourier domain. In one system (1) a signal generator (5) such as a PC sound card drives a loudspeaker (3) that serves as a transmitter and echo pulses are detedcted by a microphone (4) that serves as a receiver. Chirps transmitted by the loudspeaker (3) travel by different paths (7a and 7b) due to reflection from TILS or thermal inversion layers (2a and 2b) at different altitudes. The transmitted and echo chirp signals are compared in a mixer (6) from which various outputs (8 and 9) can be generated. One output (8) might be the magnitude of the difference between the transmitted and echo chirp tones, instant by instant, which is indicative of the altitudes of the respective TILs.