一种新的非平行轨迹机载双站斜视SAR成像算法(英文)

本文提出了一种用于非平行轨迹机载双站斜视SAR条带模式成像的新的解析算法。该算法用收、发雷达的多普勒调频率贡献比为加权系数推导了点目标回波的二维频谱。通过解目标位置相对于收、发载机飞行轨迹的耦合,将这个二维频谱中目标的距离参数和方位参数进行了分离。在二维频域内,补偿掉双站扭曲项后利用二维Chirp-Z变换(2D-CZT)校正了距离向和方位向的徙动,获得了精确聚焦的目标图像。雷达回波的二维残余徙动用沿距离向和方位向的分块来限制,推导了数据分块的条件,由此可以实现宽场景成像。仿真试验验证了这种2D-CZT算法的有效性。     

一种横向机动弹道下SAR成像算法

针对横向机动弹道下SAR成像回波方位向和距离向严重耦合、弹载SAR平台实时性要求高的特点,提出了一种基于频谱分析的扩展SAR成像算法。首先,以初始距离相同的目标作为成像处理对象,建立了横向机动下弹载SAR成像模型,分析了回波相位和瞬时距离的泰勒展开;然后,采用包含水平面速度和偏航加速度参数的相位因子依次进行距离徙动校正、二次相位补偿和多普勒中心频率补偿,实现了SAR图像的精确聚焦。该算法处理流程简单、实时性高,适合横向机动弹道下的中等分辨率的大斜视成像,给出了算法流程,仿真验证了算法有效性。     

一种孔径和频率二维稀疏的步进频SAR成像方法

 步进频率信号(SFWs)在不增加雷达系统瞬时带宽的情况下能够获得高的距离向分辨率的同时,也存在着抗干扰能力较差及其等效重复频率较低的问题,并且在方位向积累时间内由于雷达载机工作状态的变化,会导致方位向的数据录取不完整。针对上述问题,提出一种孔径和频率二维稀疏的步进频合成孔径雷达(SAR)成像方法。首先,分析了稀疏步进频率信号(SSFWs)的SAR成像模型,然后基于压缩感知理论完成距离向成像处理。其次,针对稀疏孔径的回波数据,通过构造成像算子和压缩感知重建模型的方法实现其距离徙动校正和方位压缩处理,进而获得二维成像结果。相比于传统的步进频率信号SAR成像,利用所提方法能够在少量的频率资源和雷达回波数据情况下实现准确的SAR成像。最后,通过对仿真和实测的步进频率雷达数据进行成像处理,验证了所提方法的有效性和可行性。     

大斜视FMCW-SAR波数域成像算法研究

结合FMCW(调频连续波)技术,可有效降低SAR(合成孔径雷达)的质量、成本,同时保证合成孔径雷达成像的二维高分辨率优势。针对大斜视工作模式下的FMCW-SAR成像,推导了FMCW-SAR的信号模型和波数域解析表达,分析了FMCW-SAR信号的多普勒特性,提出一种FMCW-SAR波数域成像算法。算法首先对多普勒偏移相位进行补偿,然后通过插值实现距离徙动的校正,最后进行二维逆傅里叶变换得到高精度成像结果。该方法可以在大斜视条件下获得理想的聚集成像性能,仿真实验对此进行了验证。     

基于步进频的雷达成像算法研究

在多目标情况下,雷达接收的信号是目标各点散射的矢量叠加,高分辨率的成像可以实现各目标的分离。用于目标成像有多种算法,本文使用基于步进频的卷积-反投影算法(B-P算法)对回波信号进行处理,得到了二维的目标像,同时在增加一根接收天线的情况下,也可以获得各散射点的高度信息。仿真结果验证了该算法的有效性。     

机载斜视SAR改进ETF快速成像算法

 根据机载斜视SAR(Synthetic Aperture Radar)成像模式，详细推导了任意场景位置的准确传递函数，在此基础上，提出了一种改进的ETF（Exact Transfer Function）成像算法。并推导得到了算法使用中分块处理应该满足的边界条件。由于推导过程基于准确运动模型和参考距离模型，方位相位的计算不做近似截取而是做准确计算，使得该算法具有更高的相位精度。同时该算法可运行于现有的成像系统，兼容性好；对数据分块并行运算，解决了斜视情况下大距离徙动带来的问题并且提高了运算速度。最后，点目标仿真成像结果证明了算法的有效性。     

条带模式合成孔径雷达回波数据的聚束成像算法处理

对条带模式SAR和聚束模式SAR的关系进行了研究,给出了一种如何利用聚束成像算法来处理条带模式SAR的原始回波数据的方法,这种方法基于两种模式成像处理器输入数据的不同特点和Dechirp解调原理,同时使用了频谱扩展的方法。在没有聚束模式SAR原始回波数据的情况下,可使用本文的方法利用条带SAR数据来模拟聚束SAR数据,以便研究聚束成像算法。此外在条带 SAR成像过程中,利用文中给出的算法,可以对某一小的目标区域进行精细成像。也可将此方法用于条带SAR的快视成像中。     

基于LFMCW的空空导弹弹载SAR子孔径成像方法

线性调频连续波(LFMCW)合成孔径雷达(SAR)具有体积小、功耗低、分辨率高的特点已成为当前轻小型导引头雷达技术研究的热点.本文在详细分析了线性调频连续波信号特点的基础上,针对毫米波雷达应用于空空弹精确制导的需求,对其在高速平台、前斜视条件下成像的应用,建立了精确的去调频连续波信号模型.提出了一种基于FMCW毫米波雷达的子孔径成像算法,并通过仿真实验,验证了模型与算法的正确性     

一种机载合成孔径雷达自主定位算法

针对机载合成孔径雷达(SAR)的应用,开展机载SAR自主定位技术研究,提出通过对目标所在区域多次成像进行机载SAR自主定位的算法。该算法不受载机速度和角度误差的影响,仅利用载机瞬时位置和雷达与目标之间的距离,能够大幅提高机载SAR自主定位精度;并在载机凝视目标飞行时提出基于最小二乘的定位算法,进一步提高定位精度。最后对机载SAR实测试飞数据进行处理,并与传统的基于距离多普勒(R-D)模型的定位方法进行了比较,处理结果验证了提出的算法能够大幅提高机载SAR自主定位精度。     

基于Keystone变换和MDCFT的高机动弱目标检测与参数估计

 常规雷达对隐身、超声速和高机动目标存在回波信噪比不足、距离徙动和多普勒谱扩展问题。将Keystone变换和修正离散Chirp-Fourier变换(MDCFT)相结合,提出了一种新的雷达信号处理算法。该算法通过Keystone变换补偿距离徙动问题,利用MDCFT对多普勒谱严重扩展的目标回波进行相参积累,提高目标检测性能的同时完成了对目标参数的估计,且该算法在方位向欠采样时仍可适用。最后对算法运算量及性能进行了分析,通过仿真验证了该算法的有效性。     

Role of processing geometry in SAR raw data focusing

Synthetic aperture radar (SAR) systems require that a focusing operation be performed on the received backscattered echoes (raw data) to generate high-resolution microwave images. Either due to platform attitude instabilities, or to Earth rotation effects, the SAR raw data may be acquired in "squinted" geometries, i.e., with the radar beam directed with an offset angle (squint angle) from the broadside direction. This research investigates the impact of the focusing operation carried out on squinted raw data acquisitions performed by SAR sensors operating in the stripmap mode. To this end the 2D frequency SAR processing approach is generalized with respect to conical, i.e., nonorthogonal, reference systems. This allows analysis of the geometric, spectral, and phase aberrations introduced in the images by the chosen processing geometry with respect to the acquisition, and identification of the focusing procedure that minimizes these aberrations. The whole theory is validated by experimental results carried out on simulated data. Moreover, the extension of this analysis to the interferometric case where these aberrations may have a significant role is also investigated     

A Raw Signal Simulator for Bistatic SAR

This article proposes a new efficient raw signal simulator for the bistatic synthetic aperture radar (SAR) based on 2D fast Fourier transform (FFT) to deal with cases of both ideal trajectory and trajectory deviation. It begins with analyzing the geometric configuration and the range history of the bistatic SAR in side-looking and squint modes of ideal trajectory as well as trajectory deviation. Then a detailed and mathematical study is conducted on the equivalence relation of bistatic-to-monostatic applications (BTMA) in the case of ideal trajectory and trajectory deviation. Also a set of formulas are derived for the equivalence relation between bistatic SAR and monostatic SAR on some reasonable assumptions. Therefore, the application of the simulation method based on the 2D FFT for the monostatic SAR can be extended to the case of bistatic SAR. Finally, the simulation results prove the validity of this method. By comparing the efficiency of the proposed method with that of the time domain method, it is shown that the former is a few orders of magnitude higher.     

平移不变模式双基地SAR距离聚焦深度分析

根据平移不变模式双基地合成孔径雷达的空间几何关系模型,分析了平移不变模式双基地合成孔径雷达点目标的距离徙动特性,并进一步推导出了平移不变结构双基地合成孔径雷达的距离聚焦深度计算公式。该式表明平移不变结构双基地SAR距离聚焦深度与双基地角、方位分辨力、收发分机波束指向和目标到飞机最近距离之比有关。最后通过仿真,验证了理论分析的正确性。     

机载单通道雷达实波束扫描的前视探测

针对机载单通道雷达采用合成孔径雷达(SAR)技术、多普勒波束锐化(DBS)技术等途径难以实现载机飞行路线正前方高分辨率成像问题,研究了一种利用方位实波束重叠扫描的新型机载单通道雷达前视探测方法,讨论了提高方位分辨率的可行性和适用条件。该方法根据目标回波强度受到波束扫描增益调制的特点,通过计算修正的Capon空间谱来实现方位超分辨。模拟实验表明,所提方法能够实现机载单通道雷达的前视成像,可以显著提高波束主瓣区域内强弱临近目标的分辨能力。     

A chirp scaling approach for processing squint mode SAR data

Image formation from squint mode synthetic aperture radar (SAR) is limited by image degradations caused by neglecting the range-variant filtering required by secondary range compression (SRC). Introduced here is a nonlinear FM chirp scaling, an extension of the chirp scaling algorithm, as an efficient and accurate approach to range variant SRC. Two methods of implementing the approach are described. The nonlinear FM filtering method is more accurate but adds a filtering step to the chirp scaling algorithm, although the extra computation is less than that of a time domain residual compression filter. The nonlinear FM pulse method consists of changing the phase modulation of the transmitted pulse, thus avoiding an increase in computation. Simulations show both methods significantly improve resolution width and sidelobe level, compared with existing SAR processors for squint angles above 10 deg for L-band and 20 deg for C-band     

Calibration of complex polarimetric SAR imagery using backscattercorrelations

A technique for calibration of multipolarization synthetic-aperture radar (SAR) imagery is described. If scatterer reciprocity and lack of correlation between co- and cross-polarized radar echoes (for azimuthally symmetric distributed targets) are assumed, the effects of signal leakage between the radar data channels can be removed without the use of known ground targets. If known targets are available, all data channels can be calibrated relative to one another and radiometrically as well. The method is verified with simulation and application to airborne SAR data     

Polar format algorithm for bistatic SAR

Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N/sup 2/ log/sub 2/N) performance. An O(N/sup 2/ log/sub 2/N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA.     

扫描模式航管监视雷达风电场杂波检测与抑制

近年来,全球风力发电装机容量呈指数增长。研究表明,风轮机对其附近的航管(ATC)监视雷达会产生严重影响。风轮机杂波的有效检测及抑制,对于保证空中交通安全具有重要意义。首先提出了基于回波谱宽特征的航管监视雷达的风轮机杂波检测方法。针对扫描模式下航管监视雷达频谱分辨率较低的问题,将基于自回归(AR)模型的超分辨率方法和质量中心的概念应用于雷达回波的快速谱宽和谱中心估计算法中,提高谱宽估计的精度。其次针对扫描模式下的风轮机回波数据不是一个完整周期数据的问题,基于缺省数据幅度和相位估计(GAPES)算法实现了扫描模式下风轮机雷达回波缺省数据的估计,而后利用风轮机杂波的周期性抑制风轮机杂波。该算法实现了风轮机杂波的有效检测和抑制,并且其不受限于风轮机与飞机目标在同一个距离单元的情况。仿真结果验证了所提方法的有效性。