Research On Monopulse Squint SAR Imaging Information Processing Technique

Monopulse squint SAR system works in the squint mode by radar platform lateralmaneuvering, then realizes target tracking, which is an effective means for solving theprecision tracking of important military strategy target all weather and all day. Theadvantages of monopulse squint SAR are as follows: on one side, adopting2-Dhigh-resolution SAR imaging processing can be beneficial to improve signal-to-noise ratioand the target information obtained is rich, which is beneficial for improving the ability oftarget detection and identification; on the other side, the combination of SAR andmonopulse angle measurement can not only resolve mutiple scattering points of target inrange and Doppler’s2-D plane and decrease scintillation error greatly, but also obtain thespatial position information of target with measurement of the azimuth and pitch angle ofeach resolution cells in SAR images by monopulse processing, which is beneficial forimproving the ability of target’s locating and tracking. In this paper, we mainly carry out theresearch on key technology such as monopulse squint SAR system technique, angleinformation extraction method, target location and tracking methods and so on. The maincontributions and innovations are as follows:(1) Study on the monopulse squint SAR system technology. According to thecharacters of squint SAR’s complicated geometry and non-uniform resolution, the squintSAR’s resolution characteristic is analyzed, and then a method of squint SAR resolutionanalysis based on resolution ellipse is put forward. Based on the definition of generalizedambiguity function, the expression of resolution ellipse that can describe target’s resolutioncharacter on inclined plane completely is derived; then based on imaging characters ofground plane, analytical expression of ground resolution ellipse is derived, and the methodof geometry optimization restrained by multiple parameters is put forward. Compared withtraditional methods, this method can reflect the relationship between resolution ability andparameter of system and flight path, which can provide the theoretical foundation forsystem geometry design.(2) Study on the angle extraction by monopulse squint SAR. According to thecontradiction between the measurement of instantaneous angle and the coherent integrationof SAR in monopulse squint SAR, the relationship between the angle measuring error andthe coherent accumulative time is analyzed, and the characteristic of angle modulation inSAR merging is researched. An angular motion model of target is established with time changes. A method of angle estimation based on minimum total variation in monopulseSAR principle is proposed, which can solve the angle measurement with time-varying inmonopulse SAR. The angle measurement error introduced by the attitude disturbance of theplatform and the coherent integration of SAR is analyzed. And then, according to theproblem that angle measurement error of the target is serious at the low signal-to-noise ratio,a method to measure angles of multi-target is proposed based on the angle measurementusing monopulse SAR and the topological relation of target scene. Based on strongreflectors at high SNR, the angle error of low-SNR target can be extracted in image domainusing least square method and the method is verified by real measured data, which canrealize the tracking of arbitrary pixels in SAR image and improve the tracking accuracyeffectively in monopulse squint SAR.(3) Study on the technology of target location and tracking in monopulse SAR.Monopusle SAR can obtain distance, Doppler information, pitch angle and azimuth anglesimultaneously. The four-dimensional information is obtained independently, soinformation redundancy exists in target location. A multi-dimensional joint location methodunder the condition of dive quint SAR is proposed. The target can be located by building amathematical model of the four-dimensional information, and the influence on the targetlocation accuracy by altitude variation and measurement error is reduced throughintroducing the first-order parameter of angle motion. The research of two-dimensionalimaging and one-dimensional forward-looking tracking method is developed. The aliasingof adjacent target at the tracking terminal is analyzed and the relationship between thetwo-dimensional image of high squint SAR and the one-dimensional target image inforward-looking tracking stage is researched according to the impact on azimuth resolutionby flight path. The method of target tracking based on joint estimation of target amplitudein SAR and monopulse angle is proposed to realize angle tracking of the forward-lookingtarget at the terminal.