一种基于曲线SAR的三维目标特征提取与自聚焦新算法

曲线合成孔径雷达（Curvilinear Synthetic Aperture Radar,简称曲线SAR）是一种新的三维成像模式，通过让载机作曲线飞行，曲线SAR系统能同时在方位维和高度维形成大的合成孔径。本文提出一种曲线SAR的三维目标特征提取和自聚焦新方法。新方法是建立在一种灵活的接收数据模型之上的参数化的新方法。仿真实验证明了所提方法的有效性。     

Quaternion-Based Transformation for Extraction of Image-Generating Doppler for ISAR

Inverse synthetic aperture radar (ISAR) is an imaging technique that is dependent on an object's rotational motion over a coherent processing interval. Maritime vessels and aircraft possess 3-D rotational motion, whereas it is only their ISAR contributing motion that is useful to the ISAR imaging process; the contributing motion consists of the Doppler generating axis and the effective angle of rotation. This letter presents a quaternion-based transformation that converts measured attitude and position data into an object's Doppler generating axis and effective angular rotation rate. This transformation is significant since it isolates the component of the motion that directly influences the ISAR image. It provides an alternative approach that can be used to understand the causes of blurring of most ISAR images of sea vessels as well to identify good imaging intervals for applications such as cooperative ISAR for radar cross section measurement purposes.      

2D Superresolution ISAR Imaging via Temporally Correlated Multiple Sparse Bayesian Learning

In inverse synthetic aperture radar (ISAR) imaging, the image resolution is always limited by the bandwidth and the observation time. Sparse recovery (SR) is recently proposed to improve the range resolution or cross-range resolution effectively. However, for the two dimensional superresolution case, a SR-induced range cell migration (RCM) occurs among the High-Resolution Range Profiles (HRRPs) and definitely degrades the ISAR image. After that translational motion compensation is completed, the common sparsity of HRRPs is exploited to suppress the RCM in this paper. Furthermore, by taking the temporal correlation of HRRPs into account, an ISAR imaging method based on temporally correlated Multiple Sparse Bayesian Learning is proposed to improve the imaging quality. Simulated data and real data results demonstrate the effectiveness of the proposed method.     

Migration through resolution cell compensation in ISAR imaging

Range-Doppler (RD) processing is widely used in conventional inverse synthetic aperture radar (ISAR) imaging. The unwanted translational motion of moving targets is compensated by envelope alignment and autofocus. For existing ISAR imaging algorithms, the scatterers' migration through resolution cells (MTRC) caused by the rotational motion is usually ignored. With the improvement of resolution or the increase of target size, MTRC cannot be neglected. In this letter, the keystone formatting algorithm developed in SAR is used for the MTRC compensation in ISAR. Before the keystone formatting, coherent processing must be performed on the raw phase history data. An effective approach is proposed for this kind of coherent processing. Numerical examples are provided to demonstrate the performance of the proposed approach.     

Adaptive inverse synthetic aperture radar imaging for nonuniformly moving targets

A novel adaptive inverse synthetic aperture radar (ISAR) imaging technique is proposed for targets with nonuniform motion. The proposed algorithm is referred to as the generalized range-Doppler (GRD) ISAR imaging technique and is based on the fractional Fourier transform (FRFT). By utilizing this technique, clear ISAR imaging can be achieved for nonuniformly moving targets without involvement of complex motion compensation. Simulation results have proved that the new algorithm is robust and also computationally efficient as compared with previously reported algorithms such as joint time-frequency (JTF) imaging.     

Feature-Independent Aperture Evaluator for the Curvilinear SAR

Curvilinear synthetic aperture radar (SAR), as a more practicable 3-D SAR imaging system, utilizes parametric target feature estimates extracted from the received data to reconstruct the target image. The reconstructed image quality is then impacted by the estimation accuracy of the features. In this letter, through discussing the correlation between the system parameters and the estimation performance of the curvilinear SAR, a conclusion can be drawn on how the overall location accuracy of a target is determined by the correlation between the azimuth and elevation coordinates of the flight path, compactly characterizing the curvilinear aperture. Consequently, a new index, determined only with the aperture parameters, is proposed as an aperture evaluator, which is referred to as the feature-independent aperture evaluator (FAE). FAE can be used for guiding the operational aperture design     

ISAR Imaging of a Ship Target Using Product High-Order Matched-Phase Transform

Inverse synthetic aperture radar (ISAR) imaging of a ship target is very important compared with the plane target, and the imaging condition of the ship target is more complicated than that of the plane target due to the complexity of the ship's movement. In this letter, the received signal of a ship target is modeled as a multicomponent cubic phase signal, and the product high-order matched-phase transform is proposed to estimate the parameters of each component. Then, the instantaneous ISAR images can be obtained. Results of real data demonstrate the effectiveness of the new method proposed.     

二维圆周综合孔径阵列优化及其毫米波成像特性研究

运用模拟退火算法对由20-30根天线组成的二维圆周综合孔径阵列进行优化排列,得到优化排布结果。在此基础上依据综合孔径成像的基本原理,分析了毫米波的成像算法,在u-v域运用了栅格化处理（Gridding方法）和线性插值方法。运用该成像算法对已优化排布的阵列进行了仿真,并进一步讨论了天线数目、插值方法等因素对成像特性的影响。     

Improvement of a Doppler-Radiometer Using a Sparse Array

A 2-D Doppler-radiometer has been proposed to improve the poor angular resolution of microwave radiometers, using aperture synthesis on a moving platform. In this letter, we investigate drawbacks of the Doppler-radiometer, which have not been discussed previously in detail. The imaging method is revised to be suitable for imaging of distributed sources, which is the more common situation than a point source, and then the specklelike sidelobes in the point source response are discussed. In distributed source imaging, the specklelike sidelobes in the point source response of the Doppler-radiometer severely degrade the imaging performance, so it is necessary to reduce them. The cause of specklelike sidelobes is discussed, and a sparse array is proposed to improve the imaging performance of the Doppler-radiometer. The improvement is demonstrated by simulation of the point source response, showing reduced speckle.     

非理想航迹城市建筑群MIMO下视阵列SAR三维仿真

在缺少真实下视阵列合成孔径雷达（synthetic aperture radar，SAR）系统而带来数据获取和成像算法研究等困难的当下，下视阵列SAR三维仿真的研究具有重要意义。为了还原载机平台真实的飞行航迹，验证阵列SAR技术在高层建筑物密集城区的地形测绘能力，摒弃传统仿真研究基于匀速直线运动的假设，以高度骤变的城市建筑物为对象，分析构建了多输入多输出（multiple input multiple output，MIMO）下视阵列SAR非理想航迹运动误差模型，提出了非理想航迹城市建筑群MIMO下视阵列SAR三维距离多谱勒成像算法。利用航空平台的航迹与姿态建模仿真技术，以及快速高效的回波仿真技术对成像算法进行了仿真实验，验证了方法的正确性和有效性。     

加速迭代硬阈值ISAR稀疏成像

加速迭代硬阈值(AIHT)作为一种压缩感知(CS)算法,具有计算复杂度低、内存占用小的特点,在较小数目的观测下,经过有限次迭代便能获得较好的重建效果。因此,本文将该算法应用到逆合成孔径雷达(ISAR)稀疏成像,对该方法的具体特征和适用性进行了详细分析。仿真结果表明,在相同信噪比和回波脉冲数条件下,基于AIHT的ISAR成像方法,相比于稀疏贝叶斯算法(SBL),在重建时间上缩短了至少2个量级;相比于迭代加权最小二乘法(IRLS)和平滑l0范数算法,在重建质量上提高了约3倍。经实测数据处理结果验证,在1/4原始脉冲数条件下,该方法仍具有良好的聚焦性能和压低旁瓣效果。     

Two-Dimensional Spectrum Matched Filter Banks for High-Speed Spinning-Target Three-Dimensional ISAR Imaging

In this letter, a 3-D inversed synthetic aperture radar imaging algorithm for targets in high-speed spinning is proposed based on 2-D spectrum matched filter (MF) banks. Each spectrum MF bank yields a focused slice for its corresponding scatterers. By extracting the spatial parameters from all slices, the 3-D image of the target can be constructed. Numeric simulation confirms the validity of the algorithm.      

DEM Reconstruction in Layover Areas From SAR and Auxiliary Input Data

In this letter, a methodology to overcome the layover problem and obtain the 3-D reconstruction of urban areas will be discussed. Interferometric synthetic aperture radar (SAR) (InSAR) systems allow the estimation of height profiles of the Earth surface, but in the case of urban scenarios, estimation becomes a hard task due to the presence of SAR geometrical distortions, with layover above all. First, the layover signal in InSAR images is investigated; then, a procedure to specifically manage layover areas is presented. The proposed method consists of introducing an auxiliary data exploitation, optical data or SAR shadowing, in the maximum a posteriori statistical estimation technique to improve the digital elevation model reconstruction, particularly on phase discontinuities. We test the method on simulated data, showing its effectiveness.     

Deriving time-series three-dimensional displacements of mining areas from a single-geometry InSAR dataset

This paper presents a method for deriving time-series three-dimensional (3-D) displacements of mining areas from a single-geometry interferometric synthetic aperture radar (InSAR) dataset (hereafter referred to as the SGI-based method). This is mainly aimed at overcoming the limitation of the traditional multi-temporal InSAR techniques that require SAR data from at least three significantly different imaging geometries to fully retrieve time-series 3-D displacements of mining areas. The SGI-based method first generates the multi-temporal observations of the mining-induced vertical subsidence from the single-geometry InSAR data, using a previously developed method for retrieving 3-D mining-related displacements from a single InSAR pair (SIP). The weighted least-squares solutions of the time series of vertical subsidence are estimated from these generated multi-temporal observations of vertical subsidence. Finally, the time series of horizontal motions in the east and north directions are estimated using the proportional relationship between the horizontal motion and the subsidence gradient of the mining area, on the basis of the SGI-derived time series of vertical subsidence. Seven ascending ALOS PALSAR images from the Datong mining area of China were used to test the proposed SGI-based method. The results suggest that the SGI-based method is effective. The SGI-based method not only extends the SIP-based method to time-series 3-D displacement retrieval from a single-geometry InSAR dataset, but also limits the uncertainty propagation from InSAR-derived deformation to the estimated 3-D displacements.     

GPS天-地无源双基地雷达探测海面移动目标

GNSS卫星作为一种照射源,可与地面接收机构成天-地无源双基地雷达系统,用于海面移动目标探测。但是,海面目标（如船只）反射的GNSS信号能量微弱,常被淹没在背景噪声和干扰信号中。针对这一问题,本文提出利用目标的运动特点聚集目标回波能量的目标探测方法。首先,将船只的运动轨迹看作合成孔径,采用SAR成像技术——距离多普勒算法（range-Doppler algorithm,RDA）实现目标回波能量的压缩聚集,同时抑制干扰信号（如海面杂波）。然后,使用相位梯度自聚焦算法（phase gradient autofocus,PGA）作自聚焦处理,进一步聚集目标回波能量。通过现场试验采集的数据验证了本文算法。试验结果表明,本文方法能够同时聚集多个目标回波能量,精确地估计目标到接收机的距离,并判断目标的移动方向。     

Antenna Mask Design for SAR Performance Optimization

In this letter, an effective technique for synthetic aperture radar (SAR) antenna mask design is presented for optimizing the system performance of an active phased array SAR. The SAR antenna radiation pattern has an important effect on the system performance. Therefore, the authors derived the quantitative equations for the SAR antenna mainlobe and sidelobe mask design on the basis of the system performance measures such as the range-to-ambiguity ratio (RAR), the noise-equivalent sigma zero (NESZ), and the radiometric accuracy. The antenna mask template should be designed to minimize the ambiguous signals reflected from the antenna sidelobes and maximize the system sensitivity, i.e., the NESZ, determined by the antenna mainlobe. The simple iterative method such as random-mutation hill climbing was utilized to successfully assign the sidelobe level at each ambiguous area using the derived equations. Finally, the antenna patterns were synthesized with reference to the optimized antenna mask templates using the particle swarm optimization, and the swath width, RAR, and NESZ performances were evaluated in order to confirm the effectiveness of the proposed technique.      

An optimal determination of variable antenna height and power for in-orbit SAR operations

An optimal power and antenna height determination over a wide range of incidence angles is proposed for in-orbit operations of the spaceborne stripmap synthetic aperture radar (SAR) with variable antenna height and variable radiating element power. The antenna height and the average transmitted radio-frequency power of a radiating element for each incidence angle are determined so that the mapping area can be maximized with the constraints on the signal-to-noise ratio, ambiguities, and swath width, given the SAR geometry (an altitude and incidence angles) and radar wavelength. With the receive-chain power consumption of one transmit/receive module (P/sub r/=10 mW) and the SAR instrument power consumption without the phased array antenna (P/sub I/=5 W), the illustrative design example shows that the mapping area of the proposed SAR for the maximum incidence angle (/spl eta//sup max/=75/spl deg/) is about 269.1% of that resulted from utilizing only the variable antenna height. The proposed optimization would have a more beneficial effect on applications that need the high-incidence-angle operations.     

一种顾及现势指向的上行天线阵相位中心精确标校方法

针对上行天线阵相位中心标校技术粗糙、精度不高等问题,引入精密工程测量技术测定天线实际状态,提出了一种顾及现势指向的相位中心精确标校方法。首先,利用工业摄影测量系统获取天线各姿态的型面数据,并通过最小二乘法拟合求解出现势性强的机械轴;然后,用矩阵法解算各姿态下机械轴的交点作为旋转中心;最后,基于反角度加权插值法推估得到天线在任意姿态下的机械轴,进而从投影中心沿机械轴延伸既定长度获得可靠的相位中心。以3台φ3 m上行阵天线为试验对象,通过工程控制网统一摄影测量坐标系,并按照本文方法标校天线相位中心。电信号合成效果表明,本文方法能有效克服天线自重变形、机械安装等因素的影响,实现了相位中心的精确标校,增强了上行天线阵合成信号的幅度。     

Tight integration of GPS observations and persistent scatterer InSAR for detecting vertical ground motion in Hong Kong

A method for tightly integrating GPS observations and the persistent scatterer (PS) interferometric synthetic aperture radar (InSAR) is proposed to detect vertical ground motion in Hong Kong, China. The tropospheric zenith wet delays (ZWD) derived from GPS observations at sites in the SAR scenes are used first to model and correct for the tropospheric effects in the interferograms generated from the SAR images. The vertical motion rates (VMR) of the GPS sites determined based on the continuous GPS observations obtained at the sites are then used as constraints in the PS InSAR solutions to further enhance the quality of the solutions. Data from 12 continuous tracking GPS sites in Hong Kong and 8 ENVISAT ASAR images acquired during 2006–2007 are used to demonstrate the application of the proposed method. The results from the example show that the method is capable of detecting accurately the vertical ground motion.