A Study Based On Speed Measurement Technology Of Underwater High Speed Airplane With Active Sonar

In this paper,the active sonar velocimetry is taken as the research object.The sonar reverberation and underwater background noise which affect the velocity measurement accuracy of active sonar velocimetry are studied.The main contents are as follows:Based on the theory of water entry trajectory and the hydrodynamic theory of supercavitation,the common coordinate system is established,and the forces acting on the vehicle when it enters water at high speed are analyzed,and the dynamic model is simplified by neglecting some minor effects,such as buoyancy,etc.Combined with Newton's second law of motion,the longitudinal dynamic model of the body entering the water is established.On the basis of the model of vehicle dynamics,the ambiguity diagram of sonar waveform is analyzed,combined with the characteristics of fast velocity and high acceleration,and the theory of Doppler frequency shift.A reverberation-resistant echo model of mono-frequency pulse signal is established to improve the accuracy of sonar detection.Based on the analysis of underwater background noise in acoustic echo signal,the possibility of background noise de-noising in active sonar echo by wavelet threshold de-noising algorithm is studied.The basic principle and algorithm of wavelet threshold denoising method are given.The main influencing factors of wavelet threshold denoising are analyzed,and the threshold function is discussed emphatically.Based on the existing threshold function,a threshold function between soft and hard threshold is proposed.Through the simulation experiment,it is proved that the new function threshold function has good noise reduction performance on the echo model in this paper.The accuracy of sonar measurement under interference background is improved.Using STFT as a time-frequency analysis tool,the velocity information of the de-noised echo signal is extracted.Through simulation experiments,the extracted velocity information is compared with the velocity information of the original vehicle.The effectiveness of the algorithm in active sonar velocimetry is verified.