Extraction Of Projectile Motion Features Based On Radar Polarization

With the development of the conventional ordnance technology, especially theimprovement of weapons system hitting accuracy, more precise techniques onprojectile motion features measurement are indispensable to weapons test andapproval. And the methods for measuring centroidal motion features, such asspinning rate, nutation angle, precession period and flying attitude, are neededurgently. Though radar based techniques are effective to acquire projectile motionfeatures, they have the disadvantages of less acquirable parameters, lower precisionand shorter tracking distance. It is difficult to measure centroidal motion features ofprojectiles effectively at present. The issues on mesasuring projcetile centroidalmotion features become a key difficult problem in the field of ordance test.The aim of the dissertation EXTRACTION OF PROJECTILE MOTIONFEATURES BASED ON RADAR POLARIZATION is to investigate a radar basedmethod to measure centroidal motion features of projectile by processing the indexof echo amplitude modulation, which emphasizes on discussing the realization ofprojectile centroidal motion measurement while radar transmits linear polarizedelectromagnetic wave and the projectile has polarized scatering structures. Throughanalyzing the mechanism and representation of projectile centroidal motion, radarscattering model which can express projectile motion features is established, themethods to extract motion features through radar echo is provided, projectile motionfeature measurement based on radar polariztion characteristics is realized.The scatering mechanism caused by the characteristics of geometric structureand motion is analyzed first. Echo model of the projectile with slots at the base isestablished. The index of amplitude modulation is founded as the parameter whichexpress the features of projecitle centroidal motion directly. The relationshipsbetween the parameter of radar echo and feature of projectile centriodal motion issettled, which is the theoretical basis for projectile spinning rate, precession periodand flying attitude processing.As for traditional digital demodulation method, the main factors that deterioratethe precision of spinning rate are the frequency resolution and the signal to noiseratio of the spinning component. A high resolution method based on the Chirp ZTransform is suggested, which can improve the precision of measurement and avoidnon-stationary problem induced by data downsample. As for the special types ofprojectile echo that the signal to noise ratio is comparatively low, a method based onacceleration compensation is proposed, which can improve the precision of spinningrate measurement and increase valid distance about30percent. An accurate method to process the index of amplitude modulation from radarecho is proposed based on Hilbert Transform, which can avoid the mutualinterference of the amplitude modualtion item and the frequency modualtion item.By adopting the moving Clean-IFFT method which based on iteration in the timeand the frequency domain, the spectral leakage is alleviated and the accurate indexof modulation is obtained. The relationships between the index of modulation andthe periods of precession and nutation show that the lower frequency componentsand the higher frequency components represent the features of precession andnutation respectively. The lower frequency components and the higer frequencycomponent can be constructed using the method of Empirical Mode Decomposition.Simulation and analysis show that the direct searching based precession periodprocessing method and the auto-correlation function based nutation periodprocessing method both can achieve accurate results, whose precisions are about onepercent.The effect of projectile attitude on the index of amplitude modulation of radarecho are analyzed. By the means of numerical computing, the relationship betweenthe attitude and the index that represents the attitude is established. The index isextracted from radar echo. As for the issue that α and β can not be resolve out withone equation, a method based on theoretical knowledge about the relationship andangular motion restriction is proposed. The attitude was solved out by parameteridentification technique. Simulation and data precessing results validate the methodof projectile attitude solution. The accuracy is about0.5degree.At last, ordance shooting tests and the recorded radar data processing arecarried out to testify the methods of projectile motion features extraction. Theresults of four projectile shooting tests show the validation and feasibility of themethods of spinning rate, motion periods and the attitude proposed here. Thespinning rate of base bleed projectile, the precession period and the attitude ofprojectile with slots at the base are obtain using radar for the first time. The resultsof the precession period and the attitude can be consistent with the theoreticalanalysis. There is no more accurate comparison measurement techniques in ourcountry. However, the results aslo show that the methods of the precession periodand the attitude measurement can be applicable only in the initial stage of thetrajectory that radar can track steadily, which the angle between the LOS of radarand the normal of projectile base. Usually it is valid when the angle is less than5degree. The results of nutation period processing are affected by the value of the AMindex directly. When the AM index is low, the modulation by nutation is relativeweak. And the method suggested here can not extract the period effectively. Thusproper manner of slotting grooves at the base of projectile should be adopted toincrease the AM index so as to improve the processing results.