| Generally,the overall movement of an object is accompanied by the local movement of the components of its structure,which is the generalized micro-motion.Micro-motion can cause additional frequency modulation of the radar signal.In other words,micro-motion generates sidebands about the Doppler frequency shift of the object.This phenomenon is called micro-Doppler effect.Micro-motion is the unique motion mode of the target or its component structure,so the micro-Doppler signatures contain unique motion features and structural features of the components.This type of local movement is found in many contexts,and the application range and scene are very rich.If these parameters can be effectively extracted,it will play an important role in radar target recognition,national defense security and daily production.Therefore,the effective extraction of micro-Doppler signatures and the estimation of the motion parameters are now highly anticipated research directions.In this paper,the instantaneous frequency extraction and separation of multi-component nonstationary signals,the micro-Doppler signatures of a ship target on the sea surface and its key parts with local motion,and the micro-Doppler signatures of marine corner reflector targets are studied.1.With the deepening of research on non-stationary signals,the types of such signals are diverse.For the estimation and extraction of instantaneous frequency of more complex multi-component signals,the existing methods have limited application scope and discontinuous micro-Doppler curves in the time-frequency spectrogram of residual signals.In order to solve these problems,an improved Viterbi-successive elimination method is proposed to extract and separate the instantaneous frequency of multi-component nonstationary signals with different signal intensity.The Viterbi method is used to extract the instantaneous frequency of the signal.The Mallat algorithm is used to decompose the original signal and reconstruct the remaining signal,Then the cycle is repeated until all signal components are all extracted.The proposed improved Viterbi-successive elimination method does not need to estimate the intensity of the signal component in the elimination process,and has the advantages of small calculation amount,wide application range and high estimation accuracy.2.Aiming at the study of micro-Doppler signatures of micro-motion ship targets on the sea surface,this paper is divided into two parts.The first part is the study of electromagnetic characteristics of a micro-motion ship.The second part is the study and extraction of microDoppler signatures of a micro-motion ship.The ship ’s attitude changes with the wave on the sea surface,which is the six-degree-of-freedom motion.In this paper,the six-degree-offreedom motion of the ship on the sea surface is simulated by the Public Domain Strip method,and the six-degree-of-freedom motion model of the ship is established.The timevarying scattering echo of micro-motion ship is calculated by GO-PO hybrid method,and the electromagnetic scattering echo of micro-motion ship under different conditions is analyzed.Aiming at the study of micro-Doppler signatures,a complete set of micro-Doppler signatures simulation and motion parameter extraction process of micro-motion ships is proposed,and the micro-Doppler signatures of a ship under different sea conditions,observation angles and polarization modes are simulated and analyzed.An instantaneous frequency estimation method suitable for micro-motion ship is proposed.Based on the estimated instantaneous frequency curve,a method for estimating the micro-motion ship parameters is proposed.The estimated ship motion parameters can be well consistent with the ideal values in both period and amplitude.3.For the study of the rotating shipborne radar target on the sea surface,compared with the large-scale ship target,the echo of the shipborne radar will be submerged in the echo of the ship target,so it is difficult to detect.The micro-Doppler effect provides the possibility for the detection of small but critical micro-motion components on ships.In this paper,the micro-motion model of rotating shipborne radar is established.And the motion period and structural parameters of shipborne radar are estimated based on its micro-Doppler spectrogram.Then,the micro-Doppler spectrogram of ship equipped with shipborne radar is simulated and discussed by changing the observation angle,polarization mode and sea condition.From the micro-Doppler spectrogram,more suitable conditions for detecting the shipborne radar are found,and the reasons for its favorable observation conditions are clarified through its electromagnetic scattering echo analysis.4.The target mass and size of the ocean corner reflector are small,but its radar cross section of the ship is on the same order of magnitude.So,it is often used as a passive jamming of the ship target.In this paper,the marine corner reflector is analyzed by means of microDoppler signatures.The micro-motion model of marine corner reflector is established.Based on this,the micro-Doppler simulation of corner reflector under different wind speeds and different azimuth angles is carried out.The micro-Doppler signatures are discussed,and the difference between it and the ship is analyzed.Aiming at the towed corner reflector target with translational velocity,this paper uses the fractional Fourier transform to estimate its translational parameters.The echo component generated by the translation is regarded as a linear frequency modulation signal for detection.The formula of translational parameter estimation is derived,and its translational velocity is effectively compensated.Finally,a method for extracting and separating the instantaneous frequency of multiple corner reflector targets is proposed.The extraction of the instantaneous frequency curve is divided into three parts: the segmentation of the time-frequency spectrogram,the extraction of the subspectrogram and the connection of the curve.The simulation results show the reliability of the proposed method. |
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