基于零点指向技术抑制星载SAR距离模糊算法

给出了基于零点指向技术抑制星载合成孔径雷达距离模糊的算法.该算法主要利用阵列信号处理中零点指向技术的原理,将抑制距离模糊问题转化为在指定方向上功率极小化问题,又可等效为最小二乘零点功率约束优化问题.通过将约束矩阵特征值分解和选代相结合的方法对该优化模型进行求解,得到天线方向图最优加权系数,从而精确地控制零点的深度和宽度,达到对星载SAR距离模糊有效抑制的目的.仿真结果表明了该算法的有效性.     

基于工作流的星载SAR辐射定标系统研究与设计

在对原有星载SAR辐射定标处理系统的开发和认识的基础上,分析星载SAR辐射定标处理系统的领域需求及辐射定标数据的处理流程,并对工作流技术及工作流管理系统机制进行研究.在现有的SAR辐射定标处理系统中引入工作流技术及设计思想,实现系统处理的控制逻辑与具体的实现逻辑分离,及辐射定标数据处理的自动化或半自动化,提高数据处理的效率以及系统的灵活性和适应性.     

多通道/多波束星载SAR实现高分辨宽测绘带成像综述

传统单发单收星载SAR受最小天线面积限制,不能同时实现高分辨率和大测绘带,采用多通道接收可以有效解决该问题。本文阐述了多种结构的多通道SAR系统的实现原理,分析比较了多种系统在品质因子、数据量、信噪比、信号处理复杂度以及是否存在盲区等方面的优劣和异同,并给出整体性能评价。这些结论对实际系统设计提供了理论指导和有力支撑,具有一定的参考价值。     

星载SAR的噪声干扰分析

由于在星载SAR干扰功率计算中,采用传统的雷达干扰方程很难得到某些参数,因此计算结果可能不合理。根据星载SAR的成像原理和噪声干扰机理,从定性和定量两个方面分析了对星载SAR实施噪声干扰的可行性。在不考虑成像算法及传输损耗的影响下,提出了与星载SAR的方位、距离分辨率及其运行轨道等参数有关的干扰方程,分析了与传统干扰方程的不同及影响因素。依据星载SAR系统波位设计原理,分析了雷达天线端口及其接收机通道的信干比变化,并进行了仿真、计算。研究结果适用于星载SAR干扰的工程设计及计算。     

星载SAR影像上船舶方位向模糊去除算法

目的 掌握海上船舶分布状态对于海上交通流分析和通航安全管理具有重要作用。遥感技术,特别是星载合成孔径雷达(SAR)技术的发展,为大范围海上船舶检测提供了有效的手段,但受SAR成像机制影响,海上船舶目标在星载SAR影像上通常存在着不同程度的方位向模糊噪声,这些噪声易被误判为船舶,导致船舶识别中虚警率提高。方法 本文简述了方位向模糊噪声的产生原因,提出了一种新的星载SAR影像上船舶方位向模糊去除算法,该算法的核心是构建目标方位向角度一致性、方位向位置偏移距离和方位向模糊能量衰减3个判别规则,对潜在SAR影像亮斑目标进行逐层筛选,实现船舶真实目标和方位向模糊目标的判别。结果 选取中国渤海海域和黄海海域的30 m分辨率的Radarsat-2数据进行案例分析,并与船舶自动识别系统(AIS)实测数据进行比对校验,结果表明,传统的双参数恒虚警率(CFAR)算法和基于K分布的CFAR等算法对于船舶难以剔除方位向模糊,容易造成虚警,而本文算法对实验影像的船舶方位向模糊去除准确率优于95.8%,能够有效剔除船舶方位向模糊。结论 该算法为星载SAR影像上船舶方位向模糊去除提供了新的手段,有助于提高SAR影像上船舶目标检测的准确性。     

雷达DBF处理器的研制与系统测试

随着科学技术的发展,在现代雷达系统中DBF技术的应用越来越广泛。所谓DBF技术,即数字波束形成技术,是利用数字信号处理形成独立的多个波束,各个波束的主瓣与期望方向对准,而零陷则与干扰源方向对准。本文主要对基于多片DSPs的DBF处理器的研制与系统测试进行简单的分析。     

一种抑制FMCW SAR距离模糊的方法

在调频连续波合成孔径雷达(FMCW SAR)系统中,由于FMCW SAR发射信号的特殊性,距离向模糊严重.本文从FM-CW SAR系统的成像原理出发.采用码分的方法,交替发射调频斜率相反的调频连续波,对FMCW SAR距离模糊进行有效抑制.文章给出了该方法的算法推导及仿真结果,并进行了分析,仿真结果验证了该方法的有效性.     

基于两种计算模型的星载SAR定位对比分析

距离-多普勒(R-D)模型和有理多项式(RPC)模型是星载SAR定位常用的两种计算模型,通过计算机模拟两种模型的实现过程,利用两景高差不同的radarsat-2数据,分别采集高程在45m以内的控制点和高程在128m以内的控制点,对R-D模型和RPC模型定位精度进行对比分析.分析结果表明,随着高程的增加,R-D模型定位精度提高,而RPC模型定位精度下降,因此基于R-D模型的星载SAR定位较适用于高差大的地区.     

影响星载SAR舰船检测的关键因素

由于传统舰船检测方法较少考虑海洋表面微波散射机理、星载SAR舰船成像原理等影响舰船检测的因素,适应能力有限,该文对影响星载SAR舰船检测的关键因素进行了深入研究。通过对海洋因素、舰船因素、SAR系统因素等进行深入研究,详细说明了这些因素如何影响星载SAR舰船检测,并归纳总结了星载SAR舰船检测的发展趋势,为实现星载SAR舰船自适应检测奠定了基础。     

基于能量最小化的星载SAR图像建筑物分割方法

针对星载合成孔径雷达 (Synthetic aperture radar, SAR) 图像信噪比低、建筑物目标几何变形大以及周围背景复杂的特点, 本文提出了一种基于能量最小化的星载SAR图像建筑物分割方法.基于星载SAR图像数据构造条件概率能量项, 推动变形曲线向建筑物目标边界演化; 在能量泛函模型中定义长度能量项以保证变形曲线的平滑; 在水平集方法获取的SAR图像初始分割结果的基础上, 以高分辨率光学遥感影像中建筑物目标的轮廓作为先验信息, 构造先验形状能量项约束曲线在第二阶段的演化, 最终实现SAR图像建筑物的分割.实验结果表明, 该方法显著提高了建筑物目标轮廓的分割精度.     

Wide-swath SAR remote sensing using a multiaperture antenna with waveform diversity

Synthetic aperture radar (SAR) is a well-proven remote-sensing technique; however, current single-antenna SAR systems cannot fulfil the increasing demands for high-resolution and wide-swath imaging. This paper proposes a multiaperture antenna with waveform diversity for wide-swath remote sensing. This approach employs a multiple-transmit multiple-receive antenna configuration in elevation and an orthogonal transmit waveform. In this way, multiple pairs of virtual beams directed to different subswaths can then be formed simultaneously. Equivalently, a large swath can be obtained. Furthermore, orthogonal frequency diversion multiplexing (OFDM) linearly frequency modulated (LFM) waveform and beamforming on reception are employed in this paper. The system scheme, signal model, processing algorithm, signal-to-noise ratio (SNR), and ambiguity-to-signal ratio (ASR) performance, including both azimuth and range dimensions, are investigated. Simulation results show that the proposed method can obtain an improved range ambiguity suppression, thus enabling a wider swath for remote sensing.     

Performance improvement in multi-ship imaging for ScanSAR based on sparse representation

There is always a compromise between unambiguous wide-swath imaging and high cross-range resolution owing to the constraint of minimum antenna area for conventional single-channel spaceborne synthetic aperture radar(SAR)imaging.To overcome the inherent systemic limitation,multi-channel SAR imaging has been developed.Nevertheless,this still suffers from various problems such as high system complexity.To simplify the system structure,a novel algorithm for high resolution multi-ship ScanSAR imaging based on sparse representation is proposed in this paper,where the SAR imaging model is established via maximum a posterior estimation by utilizing the sparsity prior of multi-ship targets.In the scheme,a wide swath is generated in the ScanSAR mode by continuously switching the radar footprint between subswaths.Meanwhile,high crossrange resolution is realized from sparse subapertures by exploiting the sparsity feature of multi-ship imaging.In particular,the SAR observation operator is constructed approximately as the inverse of conventional SAR imaging and then high resolution SAR imaging including range cell migration compensation is achieved by solving the optimization.Compared with multi-channel SAR imaging,the system complexity is effectively reduced in the ScanSAR mode.In addition,enhancement of the cross-range resolution is realized by incorporating the sparsity prior with sparse subapertures.As a result,the amount of data is effectively reduced.Experiments based on measured data have been carried out to confirm the effectiveness and validity of the proposed algorithm.     

A novel spaceborne SAR wide-swath imaging approach based on Poisson disk-like nonuniform sampling and compressive sensing

Since the range swath width in the conventional single channel spaceborne synthetic aperture radar(SAR)is restricted by the system parameters,there is a trade-off between the azimuth resolution and the swath width in order to satisfy the Nyquist sampling criterion.In this paper,we propose a novel spaceborne SAR wide-swath imaging scheme based on compressive sensing(CS)for the sparse scene.The proposed method designs a Poisson disk-like nonuniform sampling pattern in the azimuth direction,which meets the demand of wider swath by restricting the smallest time interval between any two azimuth samples,with the conventional sampling pattern preserved in the range direction.By a similar way to the processing procedure of spectral analysis(SPECAN)algorithm,the linear range migration correction(RMC)is realized while carrying out range compression,which can meet the demand for focusing with middle level resolution.To reduce the computation load of CS reconstruction,we propose a novel fast reconstruction algorithm based on nonuniform fast Fourier transform(NUFFT),which greatly reduces the computation complexity from O(2M N)to O(4N log N).Experiment results validate the effectiveness of the proposed methods via the point target simulation and the Radarsat-1 raw data processing in F2 mode.     

星载合成孔径雷达(SAR)斑马图仿真与研究

星载SAR中,要根据斑马图、距离模糊度和方位模糊度来选择脉冲重复频率(PRF),因此斑马图非常重要。本文根据斑马图计算公式,并根据一定的卫星轨道和雷达参数,给出了斑马图仿真;同时讨论了信号脉宽、保护时间等因素对斑马图的影响,提出了自适应斑马图设计的方法,并给出了仿真结果。     

A novel approach for wide‐swath and high‐resolution SAR image generation from distributed small spaceborne SAR systems

In this paper we investigate the possibility to produce high‐resolution synthetic aperture radar (SAR) images of wide areas from the data collected by the distributed small spaceborne SAR systems. In particular, we focus on the data processing techniques for overcoming the Doppler ambiguity effects characterizing ground echoes and achieving high‐resolution SAR images of wide areas. A novel approach is proposed, the key idea of which is to retrieve the unambiguous azimuth wide (full) spectrum signal from the received ground echoes by using a space–time adaptive processing (STAP) algorithm to overcome the Doppler aliasing effect induced by the lower pulse repetition frequency (PRF); following this operation, conventional SAR data processing tools can be applied to fully focus the SAR images. The STAP‐based approach has the advantages of simplicity, robustness and high efficiency. We also discuss the array configuration requirements, and give a platform velocity/PRF criterion for array configurations.     

A novel operation mode for spaceborne polarimetric SAR

A novel operation mode for spaceborne polarimetric SAR,named polarization space-division adding polarization code-division (PSD-PCD) operation mode,is proposed in this paper through combining polarimetric SAR with elevation digital beam-forming (DBF) on receive.In a pulse repetition interval the up-chirp LFM sub-pulse is transmitted with horizontal polarization antenna,and with some delay the down-chip LFM subpulse is transmitted with vertical polarization antenna to realize code division.After every sub-ap...     

半球面共形阵列波束综合技术研究

针对天线的抗干扰提高信噪比问题,球面阵列天线的增益在不同方向灵活可变的优点,但球面阵列天线是非线性的,没有解析解,传统的线性波束综合方法很难解决球面阵列天线复杂多约束的增益问题。为解决上述问题,使用了零陷技术。现有的方法着重干扰方向已知情况下的零陷形成技术,而对干扰方向未知多变的情况研究很少,采用改进的遗传算法用于复杂的宽角零陷形成,可以解决干扰方向未知情况下的零陷形成难题。     

MIMO SAR OFDM chirp waveform design and GMTI with RPCA based method

Multiple-input multiple-output synthetic aperture radar (MIMO SAR) has drawn wide attention for its increased degrees of freedom (DOFs) compared to the traditional multi-channel SAR (MC-SAR) system. The MIMO SAR system, which makes each antenna illuminate one subswath, can widen the range swath without decreasing PRF. One of the foremost tasks involved in the MIMO SAR system is the waveform design at the transmitter. Moreover, at the receiver, how to accurately separate the auto-correlation signal from the cross-correlation interferences is the other important issue. In this paper, an orthogonal frequency division multiplexing (OFDM) chirp signal designing method is firstly proposed, which is based on low cross-correlation interferences and good peak-to-sidelobe ratio (PSLR) rules. Using the designed OFDM chirp signals, the focused signal of MIMO SAR system matched the robust principal component analysis (RPCA) basic model. The moving target (sparse signal), clutter (low-rank signal) and noise (noise signal) can be separated directly. Hence, RPCA based method can be employed for ground moving target indication (GMTI) with no need for extracting the matched signal or suppressing the unmatched interferences. Extensive simulations demonstrate the effectiveness of the waveform designing method and GMTI with RPCA based method for MIMO SAR system.