Signal Processing of Noise Data from High-Speed Flyovers

Narrow-band spectra characterizing jet noise are constructed from flyover acoustic measurements. Radar and c-band tracking systems provided the aircraft position histories from which directivity and smear angles from the aircraft to each microphone are computed. These angles are based on source emission time. This allowed spectra to be correlated to aircraft position at the time of sound emission. Simulated spectra are included in this article to demonstrate spectral broadening due to smear angle. A detailed description of the signal processing procedures is provided. The spectra demonstrated the forward radiation of broadband shock noise of supersonic jets, confirming what has been observed in static tests. Nomenclature c0 = ambient speed of sound / = frequency fk = kth bin center frequency /„ = nth harmonic of /0 fR = Doppler shifted frequency fs = source frequency