一种精确的前斜视SAR方位高分辨分析方法

基于前斜视SAR的运动特点和波束在场景平面上的扫描规律，建立了点目标与天线相位中心的瞬时斜距模型，提出了一种新的关于前斜SAR方位向高分辨特征分析的方法，通过对前斜视SAR合成孔径长度及方位分辨特性的研究，给出了合成孔径长度与方位分辨率近似公式的使用条件并作为前斜视SAR较为精确地成像与合理简化数据处理的基本依据．     

条带式合成孔径雷达成像方法研究

提出准正侧视合成孔径雷达小斜视角度的校正方法和子孔径参考信号相位对齐算法．准正侧视合成孔径雷达(SAR)成像的校正方法采用正侧视的予孔径聚束算法对准正侧视SAR的实测数据进行成像，根据所成的像估计出小角度斜视角，采用校正的斜视子孔径聚束算法完成最后的成像．子孔径参考信号相位对齐算法本质是将各个子孔径参考信号的相位调整为同相，并构造新的聚束窗函数进行SAR成像．理论分析指出，在不增加采样数据的条件下，该方法能增大雷达方位向成像场景范围．计算机仿真结果证实了所提方法的正确性．     

斜视合成孔径声纳成像的改进距离-多普勒算法

由于合成孔径声纳的发射信号载频低以及合成孔径声纳成像高分辨率的要求,合成孔径声纳成像中菲涅耳假设不成立。基于斜视距离等效模型,放弃菲涅耳假设,给出了方位时域校正距离走动频域校正距离弯曲的改进距离-多普勒算法。该算法校正了几何形变,使得成像结果与场景完全一致。仿真结果证明了改进算法有效地提高了斜视合成孔径声纳成像的质量。     

双站SAR图像几何失真校正方法研究

针对双站合成孔径雷达(SAR)中由于发射机、接收机斜视角和速度的不同导致获取图像存在几何失真的问题,提出了一种基于坐标尺度变换的双站SAR图像几何失真校正方法．首先根据双站SAR的几何关系,详细分析了目标的斜距历程．采用等效相位中心原理,将双站SAR模型等效于单站SAR模型,结合RD成像算法,建立了几何失真校正的数学模型．最后通过该数学模型,对静止二维点阵目标的成像结果进行了几何失真校正,校正结果与地面设定的场景完全一致,从而验证了该校正方法的有效性和正确性．     

一种曲线轨迹下的弹载前斜视成像算法

针对弹载SAR存在前视盲区的问题,提出了一种导弹运动轨迹配合的前斜视距离多普勒成像算法.该算法要求导弹沿曲线轨迹飞行,这样雷达天线以一定的斜视角指向目标,前视转换为前斜视模式就能够对目标成像.考虑到曲线轨迹下距离方程复杂、成像难度较大,首先获得距离方程的高阶近似表达式,并在时域作距离徙动校正;再利用级数反演法获得二维频率域表达式;最后通过二维匹配滤波获得成像结果.仿真实验验证了该算法的有效性.     

弹载SAR下降段成像算法研究

弹载SAR下降段成像中,弹体较大的下降速度和加速度将导致SAR回波信号的多普勒调频率沿方位向变化,影响方位聚焦.针对该问题,提出了一种利用方位非线性变标(NLCS)的弹载SAR下降段成像算法.该算法在距离徙动校正和距离压缩处理之后,通过引入方位非线性变标操作,补偿变化的多普勒调频率,并校正图像方位畸变,从而改善了方位聚焦深度和聚焦质量.数据仿真结果验证了算法的有效性.     

一种新的大斜视TOPS SAR全孔径成像方法

针对大斜视模式导致回波信号距离向和方位向耦合严重,循序扫描地形观测模式波束指向的变化导致全孔径回波信号的方位带宽大于系统脉冲重复频率,引起方位谱模糊的问题,提出了一种基于修正距离徙动算法和方位谱分析的全孔径成像算法.对于全孔径数据,首先通过方位预处理获取信号无模糊的二维频谱,然后采用修正距离徙动算法进行距离徙动校正,最后通过谱分析技术和方位去斜技术将信号聚焦在方位频域.仿真实验和实测数据结果验证了该算法的有效性.     

利用SPECAN算法的聚束SAR成像处理

讨论了距离向去调频聚束模式SAR信号的回波模型及特点,通过对聚束SAR信号的时、频域关系的分析,给出了适合去调频后的聚束SAR数据的成像算法。该算法结合了SPECAN算法高效和标准条带成像算法精确的优点,首先采用SPECAN算法对原始数据距离向去斜,其次采用距离-多普勒算法实现方位精确聚焦,与传统的距离-多普勒算法相比,成倍地降低处理的数据量,从而可实现聚束SAR的实时成像处理。对Ku波段实际飞行数据采用该算法压缩得到高分辨率的图像,验证了理论分析的正确性和所用方法的可行性。     

机载大斜视SAR的快速简易成像方法

大斜视角下SAR信号特点表现为大的距离走动和小的距离弯曲,这使得采用时域距离走动校正和二维可分离成像方法成为可能．但方位场景较大时要考虑聚焦深度的限制,须采用复杂的算法．提出一种将成像和校正几何形变相结合的分段处理方法,段与段之间可以完全衔接,实现快速连续实时成像．仿真试验和实测数据成像均证明快速简易方法是可行的．     

中轨SAR海面运动舰船回波建模研究

中轨SAR具有宽测绘带及重访时间短的优势,是低轨SAR与高轨SAR的重要补充。然而,相对于低轨SAR,中轨SAR具有合成孔径时间长,轨道特性复杂等特点,常规斜距模型不适用于中轨SAR。考虑了回波非"停-走-停"的情况,结合轨道及运动舰船特点,对中轨SAR舰船目标斜距模型进行定量化分析。得到舰船在静止、匀速运动、加速运动时四阶斜距模型能够满足成像要求,当受海浪影响时四阶斜距模型将失效的结论。最后实现中轨SAR海面舰船回波精确建模。     

斜视圆迹环扫SAR模式特性分析及成像方法简

Circular scanning SAR(CSSAR) is a new mode for fast large area SAR imaging by increasing the azimuth scanning speed. The squint CSSAR possesses the advantages that the side-looking CSSAR does not have due to its unique observing direction. However, the available signal characteristic analysis and imaging method for side-looking CSSAR become questionable when applied to the squint CSSAR. This paper establishes the echo range model and analyzes several parameters such as azimuth scanning speed, Doppler characteristics and azimuth resolution according to the moving feature of squint CSSAR. Furthermore, the internal relationship between the squint CSSAR and the classical stripmap mode is revealed. The range approximation model as well as the corresponding imaging method is analyzed. Computer simulation results validate the conclusions and the imaging method.     

New method for azimuth-dependent correction of highly squint missile-borne SAR subaperture imaging

Squinted imaging is one of the most important modes in the missile-borne synthetic aperture radar (SAR). Usually, from the view of practical applications, the missile-borne SAR adopts subaperture processing in order to implement quick look imaging. In the highly squint mode, the echo signal couples greatly between range and azimuth, so traditional algorithms perform the linear range walk correction in the azimuth time domain firstly to mitigate greatly the range-azimuth coupling, which causes the problem of position dependent azimuth phase, resulting in the azimuth uniform processing disabled and impacting the azimuth depth of focus (DOF). Based on the deep analysis of the instantaneous slant range model in the highly squint missile-borne SAR, this paper proposes high-order phase filtering to correct azimuth-dependence for implementing the identical azimuth-focusing processing. Simulation results validate the effectiveness of the proposed algorithm.     

Imaging method for highly squinted SAR with spatially-variant doppler centroid correction

In the high squint SAR imaging, the linear range walk correction (LRWC) is usually adopted to mitigate the coupling between range and azimuth. The conventional algorithms only consider the effects of Doppler frequency modulation rate dependence but ignore the spatially-variant Doppler centroid; this will affect the final focusing. In this paper, the effects of spatially-variant Doppler centroid in high-squint synthetic aperture radar (SAR) are analyzed and discussed, and a modified nonlinear chirp scaling algorithm with spatially-variant Doppler centroid correction in high squint SAR azimuth processing is proposed in order to improve the quality of the final focusing. Both simulation and real data processing validate the effectiveness of the proposed method.     

Imaging algorithm for highly squinted SAR data processing based on phase disturbing

For quick look imaging, a phase disturbing algorithm (PDA) for focusing synthetic aperture radar (SAR)subaperture data acquired at a high squint angle is proposed. First, the signal model is addressed and then the range processing and azimuth processing are analyzed in detail. The PDA performs the linear range walk correction (LRWC) in the time domain and the range cell curvature correction (RCCC) in the frequency domain to mitigate the range-azimuth coupling. Additionally, a disturbing phase is introduced in the frequency domain to remove the variation of the Doppler chirp rate with the azimuth position caused by LRWC in the time domain,and so an identical reference function can be employed in azimuth processing. Simulated results and raw data processing validate the effectiveness of the proposed algorithm.     

一种新的斜视波束指向SAR信号处理方法

针对斜视波束指向合成孔径雷达(BS-SAR)信号时,存在距离向与方位向的强耦合性及方位频谱的模糊问题,提出了一种基于方位重采样的信号频谱处理方法．线性距离走动校正后对信号频谱进行方位向重新采样,将其完全等效为正侧视合成孔径雷达信号的频谱．针对斜视BS-SAR,将方位重采样与谱分析技术相结合,得到无模糊及方位空变的二维频谱;再采用传统的正侧视BS-SAR算法,实现对场景的聚焦．仿真实验表明,文中方法可以有效应用于斜视BS-SAR的数据处理中．     

脉内聚束SAR方位高分辨率宽测绘带成像

针对星载合成孔径雷达(SAR)方位高分辨与宽测绘带之间的矛盾,提出脉内聚束SAR模式实现高分辨宽测绘带成像．建立了脉内聚束SAR模型,分析了脉内聚束SAR回波信号特性,得出脉内扫描技术会导致不同方位子场景上散射点相互叠加引起距离模糊的结论．针对该距离模糊,利用俯仰维多孔径进行空域滤波解模糊;并分析了地形起伏对成像结果的影响．脉内聚束SAR利用脉内扫描获得更长的合成孔径,以此实现高的方位分辨率; 同时在采用低脉冲重复频率的情况下,获得宽测绘带,从而实现了高分辨宽测绘带成像．仿真实验结果验证了该方法的有效性．