Acoustic identification and classification of helicopters - using mathematical model transforming ambient noise into frequency domain and identifying rotor frequency ratio from power spectrum

摘要

Acoustic helicopter identification and classification from ratios of main and rear rotor frequencies involves repeatedly detecting background noise and feeding it into a mathematical model which transforms it into the frequency domain. A derived difference power spectrum is transformed into a multiplicatively weighted frequency difference power spectrum. A frequency diagram is generated in which the highest amplitude is defined as the main rotor frequency. The ratio of the second highest amplitude, corresp. to the rear rotor, to the highest amplitude is compared with typical stored values to determine the type. USE/ADVANTAGE - Helicopter types can be selected from undefined frequency mixes.