16 April 2008 Helicopter detection using harmonics and seismic-acoustic coupling
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Abstract
Unattended ground sensors (UGS) are routinely used to collect intelligence, surveillance, and reconnaissance (ISR) information. Unattended ground sensors consisting of microphone array and geophone are employed to detect rotary wing aircraft. This paper presents an algorithm for the detection of helicopters based on a fusion of rotor harmonics and acoustic-seismic coupling. The main rotor blades of helicopters operate at a fixed RPM to prevent stalling or mechanical damage. In addition, the seismic spectrum is dominated by the acoustic-seismic coupling generated by these rotors; much more so than ground vehicles and other targets where mechanical coupling and a more broadband acoustic source are strong factors. First, an autocorrelation detection method identifies the constant fundamental generated by the helicopter main rotor. Second, key matching frequencies between the acoustic and seismic spectrum are used to locate possible coupled components. Detection can then be based on the ratio of the coupled seismic energy to total seismic energy. The results of the two methods are fused over a few seconds time to provide an initial and continued detection of a helicopter within the sensor range. Performance is measured on data as a function of range and sound pressure level (SPL).
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T. Raju Damarla, T. Raju Damarla, David Ufford, David Ufford, } "Helicopter detection using harmonics and seismic-acoustic coupling", Proc. SPIE 6963, Unattended Ground, Sea, and Air Sensor Technologies and Applications X, 69630W (16 April 2008); doi: 10.1117/12.776899; https://doi.org/10.1117/12.776899
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