Research On Ground-Based/Spaceborne Inverse Synthetic Aperture Radar Imaging For Space Targets

As the increasing of aerospace activities,the space environment is becoming more and more crowded.In order to ensure the safety of space activities and maintain the stability of the space environment,a comprehensive and systematic awareness of the space situation is urgently needed for countries all over the world.As the main method of the space situation awareness,the space surveillance technology has attracted more and more attention.Due to the all-time,all-weather,and long-range working ability,radar becomes an important part in the space surveillance system.With the ability of space target imaging,the inverse synthetic aperture radar(ISAR)has also become a powerful tool in space monitoring and observation,and plays an important role in the classification,the recognition,and the mechanical damage diagnosis of the space targets.The existing space surveillance system is mainly consists of the ground-based system.In order to expand the scope of the target surveillance and improve the flexibility of surveillance system,the further development of the space-based space surveillance technology is required.The spaceborne radar has the unique advantages such as not being affected by illumination conditions.Spaceborne radar imaging for space targets has become an important development direction of the space surveillance technology.In this paper,the ISAR imaging methods for space targets have been studied comprehensively.Including the cross-range scaling of the ISAR image for space targets,the parametric range-instantaneous Doppler(RID)algorithm of the ground-based ISAR imaging for space targets,and spaceborne ISAR imaging for space targets.In the research of the parametric RID method of ground-based ISAR,the target is divided into two categories in this paper,including the steady space target with only the orbit movement and the maneuvering space target with attitude adjustment or in slow tumbling.The characteristics of the radar echo from the two kinds of targets have been analyzed respectively,and two different parametric RID imaging methods are respectively proposed.Theoretical analysis,simulations and real data experiments have been accomplished in this paper from the above aspects,the main contents are as follows:1.In order to solve the cross-range scaling problem of the ISAR imaging for space targets,a two-step accurate cross-range scaling algorithm based on the geometric relationship and the signal parameter estimation is proposed.For the target with the predicted orbit information,the method makes an effective use of the prior information,based on the analysis of the fundamental configuration for the space target ISAR imaging,a rapid cross-range scaling for the target image can be completed through the geometric relationship between target and radar.For the target without the prior orbit information,the method first uses the blob detection operator to extract the isolated scatterers of the target,and then uses the integral cubic phase function method to estimate the chirp rate of the echo from each scatterers.Finally,the linear relationship between the chirp rate and the corresponding range position of each scatterer is used to estimate the equivalent rotation velocity of the target during imaging,which can be used to complete the cross-range scaling for the ISAR images.Simulation and real data processing results have been used to verify the effectiveness of the proposed method.The results show that the proposed method can accomplish the cross-range scaling of the ISAR image for space targets accurately.2.To solve the problem of ISAR imaging for steady space targets with only the orbit movement,the parametric RID imaging method based on smoothed integrated high-resolution time-frequency-rate representation is proposed.First,the radar echo from a range cell is modeled as a multi-component LFM signal based on the characteristics of the echo of the orbit-moving target.Then,the chirp-rate of each component is estimated using the smoothed integrated high resolution time-frequency-rate representation method.After that,the instantaneous Doppler spectrum of the received signal from each range cell can be reconstructed according to the estimation results.At the same time,the RID imaging results of the target can be obtained.The effectiveness of the proposed imaging method is verified by the real data processing results,and the accuracy of the proposed imaging method in reconstructing the target image is demonstrated by the comparisons with similar methods.3.To solve the imaging problem of the maneuvering space target with attitude adjustment or in slow tumbling,the coherent integrated smoothed generalized cubic phase function algorithm is proposed for the multi-component cubic phase signal estimation,and a parametric RID imaging method based on the algorithm is proposed.First,on the basis of the analysis of the three-rotational features and the characteristics of the echo,the echo from a single range cell is modelled as a multicomponent cubic phase signal.Then,the characteristic of the cross-terms of the generalized cubic phase function kernel is analyzed,and the coherent integrated smoothed generalized cubic phase function algorithm with cross-term suppression is proposed.Finally,the echo parameters are estimated using this method,and the instantaneous Doppler spectrum of the received signal from each scatterers can be reconstructed accordingly and the RID images in corresponding time instant can be obtained.The effectiveness of the proposed method are verified by simulations in different signal-to-noise ratios and real data processing results.The anti-noise performance,cross-term suppression performance,and the estimation accuracy of quadratic chirp-rate estimation are demonstrated by comparisons with similar imaging methods.4.To solve the motion compensation problem caused by low signal-to-noise ratio and large imaging accumulation angle in spaceborne ISAR imaging for space targets,a parametric translational motion compensation method based on the parabola detection and the minimum entropy is proposed,as well as a parametric rotational motion compensation method based on minimum entropy.The proposed translational motion compensation method fit the change of the target range respect to slow time as a parabolic expression,the parabola detection method based on Hough transform is used firstly to obtain the initial estimation of the target range to complete the initial translational motion compensation of the radar echo.And then,the residual error of the initial compensation is estimated by using the parametric translational motion compensation method based on minimum entropy,and the accurate translational motion compensation can be completed.The proposed rotational motion compensation method estimate the rotation center and the equivalent rotational velocity simultaneously,the rotation compensation and cross-range scaling of the target image can be completed by using the estimation results.The effectiveness of the proposed the translational and the rotational motion compensation methods are verified by simulations in different signal-to-noise ratios and real data processing results.The accuracy of the proposed translational motion compensation method is demonstrated by comparisons with similar imaging methods.