Research On Detection And Identification Method Of Low Altitude Turbofan Aircraft Based On Acoustic-seismic Fusion

Militarily,passenger aircraft mistakenly identified by the missile system as fighter aircraft destroyed tragedies occur from time to time,so it is necessary to effectively monitor and identify low-altitude aircraft;For civilian use,environmental protection departments carry out noise monitoring near the airport,which requires the detection and identification of low-altitude aircraft.Common low-altitude aircraft can be divided into turbojet aircraft,turbofan aircraft and turboprop aircraft according to the engine,in which the turboprop aircraft has obvious spectral characteristics,easy to identify,while the turbojet aircraft signal is similar to turbofan aircraft signal,difficult to distinguish.At present,there is less research on this aspect at home and abroad,and there is a lack of effective identification methods.Therefore,this paper tries to study the low-altitude turbofan aircraft as the object of detection and identification,and when the identification results exclude the turbofan and turboprop aircraft,it is classified as a turbojet aircraft.The difficulty of low-altitude turbofan aircraft detection is that the common aircraft detection method is not suitable for low-altitude and common aircraft identification methods are difficult to distinguish between turbojet aircraft and turbofan aircraft.Infrared detection is susceptible to weather,radar detection has a low-altitude blind spot,the available detection technology is mainly acoustic and seismic detection.Among them,the acoustic signal has the advantages of high frequency information and high signal-to-noise ratio,but at the same time,there are problems of fast attenuation speed and susceptible to ground masking and ground reflection.Although most of the existing studies identify the test turbojet engines and turbofan engines by the high-frequency characteristics of acoustic signals,it is difficult to detect the high-frequency characteristics in the actual low-altitude aircraft acoustic signals.The seismic waves formed by the propagation of acoustic waves to the ground coupling,which are not affected by the ground blocking and ground reflection,have the advantages of slow attenuation,rich information of low frequency band and long detection distance,but there are some disadvantages of narrow signal band range and weak signal strength.There are few studies on the identification of low-altitude turbofan aircraft by seismic waves,and it is not clear whether there are features in low frequency band that can distinguish low-altitude turbofan aircraft from turbojet aircraft.In order to solve the above problems of low-altitude turbofan aircraft detection and identification,under the funding of elastic wave detection research project,this paper has carried out a research on the detection and identification method of low-altitude turbofan aircraft based on acoustic-seismic fusion.Considering that turbojet aircraft and turbofan aircraft may have distinguishable low frequency characteristics,combined with the technical characteristics of acoustic and seismic detection,the research on low-altitude turbofan aircraft detection and identification is carried out by using acoustic-seismic fusion method,which mainly includes the following:First of all,from the low-altitude aircraft detection to carry out research.Through analysis,it is found that the aircraft signal is non-stable,which will lead to unstable time domain characteristics,but the expansion window for the sake of feature stability will lead to poor detection real-time.Therefore,by analyzing the peak envelope of aircraft signal,the paper puts forward the EOP(Envelope of Peak,EOP)characteristics which are not affected by the non-smoothness of aircraft signal,combined with acoustic-seismic fusion and support vector machine to achieve low-altitude aircraft detection.The accuracy of simulation detection is 95.6%,and the accuracy of actual data detection is 88%,false positive rate as high as 19.9%.After analysis,the reason for the low detection rate of the actual data algorithm is the complexity of the actual environmental noise,so the paper also studies the detection of low-altitude aircraft under complex environment,and puts forward a method to suppress the noise by analyzing the peak noise characteristics that seriously affect the detection rate of low-altitude aircraft.The detection accuracy of the measured data after denoising is 94.1%,which is 6.1% higher than before and false positive rate reduced by 12.5%.In order to further solve the problem of the identification of low-altitude turbofan aircraft,the paper analyzes the differences in the low-frequency band characteristics of low-altitude turbojet aircraft and turbofan aircraft from the simulation and measured data,and puts forward the characteristics of spectrum energy distribution,which provides a basis for the follow-up identification method.Finally,in order to solve the problem of the identification of low-altitude turbofan aircraft,the paper analyzes the difference of low-frequency characteristics of low-altitude turbojet aircraft and turbofan aircraft from the simulation test and measured data,and puts forward a acoustic-seismic fusion low-altitude turbofan aircraft identification method based on the spectrum energy distribution characteristics.Considering the practical application environment,the simulation test experiments on adding Gaussian white noise with a signal-to-noise ratio of-5d B-25 d B to the analog test signal show that the accuracy of recognition can reach more than 95% when the signal-to-noise ratio is 15 d B-25 d B.The results show that this method can effectively detect and identify low-altitude turbofan aircraft.