Research On The Imaging Technologies For Terminal Guidance Missile-borne SAR

Synthetic Aperture Radar(SAR)is a kind of all-weather,day-and-night high resolution microwave remote sensing imaging Radar.It’s through this that high resolution image similarly to optical cameras can be obtained in low visibility conditions.SAR was applied to missile platform for active 2D imaging.The image of the target area for matching processing,correcting accumulation errors and initial localization errors for Inertial Navigation System(INS).This was done by the missile-borne SAR,which is an effective way of improving precision of precision-guided weapons.The missile-borne SAR with longer range,high resolution imaging can be the detection,recognition and automatic options for attacking under the backgrounds of the far distance,the strong ground clutter,sea clutter.Unlike the traditional approach for airborne or spaceborne SAR,a high-speed dive ballistic missile terminal guidance stage,flight speed,there is a certain speed and acceleration in the vertical direction.Therefore,the terminal guidance missile-borne SAR imaging is needed to solve the following problems:(1)diving SAR imaging;(2)high squint SAR imaging;(3)image matching for missile-borne SAR;(4)the design and engineering of SAR simulation experiment system.In this paper,the following research is carried out.1、The high resolution imaging technology of the high squint SAR mode in terminal guidance is studied.Based on the characteristics of the terminal guidance movement with high squint,the geometrical model of the high squint missile-borne SAR in terminal guidance is established.Through the analysis of the phase error introduced in the time domain approximation of the instantaneous slant range of the projectile-target,the relation between the range migration and the squint angle is obtained.Combined with Fractional Fourier Transforn(FrFT),it is easy to deal with the characteristics of linear frequency modulation signal,so as to the high squint missile-borne SAR imaging algorithm based on FrFT applicable to terminal guidance.The algorithm uses two dimensional FrFT to focus in range and azimuth,and the simulation is implemented for demonstrating the validity of the proposed method.2.The imaging technology of the spotlight SAR,with high squint in terminal guidance is studied.Based on the characteristics of the missile-borne spotlight SAR platform movement in terminal guidance,the model of the missile-borne spotlight SAR echo in terminal guidance,is established by using the high order approximation model.An improved FS imaging algorithm is proposed for the missile-borne spotlight SAR with high squint by the analysis of the characteristics of the geometric and movement.The algorithm firstly corrected the linear range migration in time domain and then corrected the reference function,defined by the original algorithm.The range migration of the target is adjusted to the range migration of the scene center,through the corresponding frequency scaling factor.And then by correcting the range migration and removing the residual video phase,through the block shift and the second range compressing,it avoids the Stolt interpolation instead of Fourier transform and complex multiplication and reduce the calculation.At the same time,the contradiction of the extension points increasing with the highr squint in which original algorithm is solved by adopting a novel azimuth scaling function.The simulation is implemented for demonstrating the validity of the proposed method.3、The technology of image matching for the missile-borne SAR is studied.An image matching algorithm is presented based on improved SIFT to ameliorate the limitation of traditional SIFT algorithm.This algorithm utilizes constant false alarm rate property of ROEWA operators.The new eigenvector generated by the improved feature descriptor enhances the algorithm robustness to the speckle noise,reduces the dimension of the SIFT features operator,and accelerates the computational speed for SIFT,which improves the efficiency of image matching for missile-borne SAR.The simulation is implemented for demonstrating the validity of the proposed method.4、The signal processing technology of the missile-borne SAR imaging based FPGA+DSP is studied.According to technical parameters,the design scheme of the SAR transceivers front-end is determined.With the hybrid integration technology,the front-end of LFM transceiver is designed.The missile-borne SAR signal processing system is designed on the basis of analyzing cooperative working model on FPGA and DSP.In system,the SAR imaging algorithm is processed by DSP and LPF,Orthogonal transforms of the echo is pre-processed by FPGA.The exactness and feasibleness in the simulation experiment system of the SAR imaging are verified by simulation and test in outer field orbital.