Research On Micro-motion Parameters Estimation Of Space Cone-shaped Targets Based On HRRP Sequence

Space cone-shaped target recognition, a key technique of ballistic missile defense system, has incurred abroad attention. Wideband radar, with its high range resolution, has the ability of detecting the threatening target from a target group, and the echoes involve rich information of a target. Therefore, wideband radar plays an important place in the space cone-shaped target recognition. At the present stage, the similarity of the shape and electromagnetic characteristic between a decoy and space cone-shaped target becomes increasingly higher. In this situation, micro-motion characteristic based recognition methods in space cone-shaped target recognition have aroused general interest. Combining the wideband radar echo and micro-motion characteristic of the space cone-shaped target, this dissertation mainly focuses on range alignment, micro-motion characteristic extraction and estimation methods of the target’s structure parameters and micro-motion parameters. The main work in this dissertation can be summarized as follows:1. Wideband echo models of space cone-shaped targets are istablished. In midcourse of the ballistic trajectory, translation and micro-motion coexist in the space cone-shaped target. Firstly, the translation of the target is analyzed to show that the trajectory of the space cone-shaped target in midcourse can be forecasted, only if three translation parameters at any time are given. Then based on two scattering center models, three kinds of micro-motion are studied. Finally, combining the motion characteristic of the space cone-shaped target and the chirplet decomposition technology, the analytic form of the wideband radar echoes of the space cone-shaped target is derived. And the electromagnetic data is used to verify its validity.2. The problems of range alignment for the space cone-shaped targets are studied. And a novel range alignment method based on the polarization scattering characteristic is proposed. Firstly, based on Capon and amplitude and phase estimation (APES), P-CAPES is developed to estimate the number, positions and polarization scattering matrixes of the scattering centers. P-CAPES, which has super-resolution ability, avoids the association problem among the full-polarization radar echoes. Then, based on polarization scattering matrix, the definition of the polarization similarity is given, which represents the similarity between two scattering centers. Finally, range alignment for targets with micor-motion is realized by using polarization similarity.3. Based on multiple target tracking (MTT) algorithm, an extraction method of micro-motion characteristic from wideband radar echoes is studied. When the micro-motion in the high resolution range profile (HRRP) is evident, MTT algorithm is applied to track the micro-motion curves on HRRP sequence. Otherwise, the micro-Doppler frequency of the space cone-shaped target is analyzed. Time-frequency transform is applied on the phase information, which is obtained from the wideband radar echo, to get the time-frequency distribution (TFD). Meanwhile, the relationship between TFD and micro-Doppler frequency of the space cone-shaped target is indicated. MTT algorithm is applied to track the micro-Doppler frequency curves in the TFD, which are assumed to be the tracks of maneuvering targets. Thus the micro-Doppler frequencies of each equivalent scattering center are extracted via the method.4. The estimation methods of space cone-shaped target’s structure parameters and precession parameters are discussed. Fistly, based on the midcourse ballistic trajectory a novel estimation method by using single-apect HRRP sequence is proposed. In this method, utilizing the midcourse ballistic trajectory and the space cone-shaped target’s reentry characteristic of ’zero angle of attack’, the angle between radar line of sight (LOS) and precession axis is calculated. Then a circular correlation coefficients based method is applied on the HRRP sequence to estimate the precession period. While the wideband radar echoes are coherent, the translation parameters can also be obtained. When the precession period and the angle between LOS and precession axis are known, the structure parameters and precession parameters of the target can be estimated by using the micro-motion curves extracted from HRRP sequence.When the angle between LOS and precession axis can’t be obtained, a method for estimating the target’s parameters by using two-aspect HRRP sequences is proposed. Without additional information, the method could estimate the target’s structure parameters and micro-motion parameters by using two group micro-motion curves extracted from two-aspect HRRP sequences respectively. And when the angle between LOS and precession axis is known, the method can improve the estimation accuracy.To extract the characteristic of micro-motion from HRRP sequence, there is a certain requirement of the echo’s signal to noise ratio (SNR). When the SNR cannot meet the requirement, the estimation methods are invalid because the micro-motion curves cannot be extracted from the HRRP sequence effectively. In the view of this situation, after giving the approximate expression of the micro-motion equation, a generalized Radon transform is proposed to extract the micro-motion characteristics in the condition of low SNR. Considering the shielding effect of scattering center, corresponding parameter estimation methods are given in the different ranges of viewing angle which have different number of scattering centers. And the proposed method can also effectively estimate the parameters even if the scattering centers are interrupted in the HRRP sequence.