基于Vega软件的SAR实时仿真技术

进行合成孔径雷达（SAR）成像仿真是研究成像雷达的一个重要手段。本文在分析SAR成像仿真机理的基础上,提出了一种利用视景仿真软件Vega进行SAR实时成像的仿真方法。利用软件平台VC＋＋、Multigen Creator和Vega设计机载合成孔径雷达（SAR）成像仿真系统,分析了影响机载SAR成像质量的各种参数,论述了利用Vega的雷达仿真模块——RadarWorks开发机载SAR成像仿真软件的流程以及整体系统的实现等关键技术。     

干涉合成孔径雷达海浪遥感研究

海浪是重要的海洋环境参数, 它对港口建设、海上航行、油气田开发等具有重要的意义。合成孔径雷达(Syn thet ic Apertu re Radar, SAR ) 是目前大范围测量海浪的主要工具, 用它来估计海浪主波系统的波长和传播方向比较好, 但要定量的提供海浪的振幅以及SAR 图像强度与实际海面的关系是相当困难的, 而且由SAR 图像获取海浪方向谱也比较复杂。沿航迹干涉合成孔径雷达(Along-Track Interferometric Synthet ic Aperture Radar,ATI-SAR ) 是在平台飞行方向上安置两根天线的双天线合成孔径雷达。相对于合成孔径雷达, 真实孔径雷达调制传递函数对沿航迹干涉合成孔径雷达相位图像的影响很小, 因此沿航迹干涉合成孔径雷达更适合测量海浪。详细介绍了沿航迹干涉合成孔径雷达海浪遥感的成像机制, 为进一步反演海浪方向谱奠定了基础, 最后针对目前研究存在的问题以及今后有待研究的方向进行了探讨。     

机载SAR的定位误差分析与计算

对目标进行定位是合成孔径雷达的一项重要功能。文章主要分析了由惯性导航系统引入的未知误差对机载合成孔径雷达定位精度的影响问题:首先建立SAR目标定位几何模型,然后从成像的角度分析惯导系统引入的误差对定位精度的影响,推导了定位误差的数学表达式,为SAR系统定位精度指标设计提供了理论基础。     

全极化合成孔径雷达海浪遥感方法

提出了一种利用全极化真实孔径雷达测量方位方向和距离方向海浪斜率的新方法,该方法不同于极化方向角估计海浪方位向斜率方法,利用两种线极化图像信息将有关弱极化项剔除(流体动力学调制),获得仅包含倾斜项和极化调制项的雷达成像公式。利用机载SAR取代真实孔径雷达进行海浪反演,获得了与浮标致的结果。另外,在速度聚束模式情况下,推导了双极化合成孔径雷达图像谱同海浪谱的非线性变换关系。     

改进的斜视机载合成孔径雷达RD成像算法

距离一多普勒算法是合成孔径雷达成像处理中最常用的方法之一,通过在距离一多普勒域中插值来校正距离徙动.研究了机载合成孔径雷达在小斜视角下的成像算法,给出了机载斜视SAR的空间几何模型和回波信号特点.提出了改进的RD算法进行距离走动的校正,避免了插值运算,从而降低了计算复杂度.方法能满足小斜视角下的机载SAR成像处理,并进行了计算机仿真.理论分析和仿真结果表明:改进的RD算法是有效的,在峰值旁瓣比和积分旁瓣比几乎不变的情况下成像时间缩短了近3倍.     

基于TMS320C6701的机载SAR方位向处理的实时实现

机载合成孔径雷达可以在载机飞行的同时获得高分辨率合成孔径雷达图像。由于合成孔径雷达成像具有很多原理性优点,它在军事和民用领域都取得了广泛的应用。方位处理是合成孔径雷达成像算法中重要的一步,由于算法本身的复杂性和雷达数据的高速率,方位向处理的实时实现具有很大的挑战性。介绍了自主研发的、采用TI C67 DSP作为核心处理芯片实现方位向处理的高速信号处理系统。通过优化的结构设计和软件流程,有效保证了硬件资源的利用效率,成功实现了设计目标。     

合成孔径雷达在海洋遥感中的应用

就合成孔径雷达的基本特征及其主要功能、海洋应用的要求等方面作了简单介绍,重点论述了合成孔径雷达在海浪遥感和海洋成像遥感中的应用,并提及其他的海洋应用。对合成孔径雷达在海洋遥感各领域中的应用前景作了探讨。     

机载SAR实时成像系统自聚焦方法研究

发展我国自主产权的机载SAR（合成孔径雷达）实时成像系统，对于军事国防、资源探测、灾害预报等领域均具有重要的意义，在SAR成像算法中，自聚焦的好坏是影响图像分辨率的关键因素，但是因为自聚焦算法的复杂性，国内目前尚未有效地解决它在实时环境中的实现问题，从而使得实时成像的质量比较差，提出了一种利用GPS（全球定位系统）数据改善机载SAR实时成像系统自聚焦性能的实现方法，并在自主研制的机载SAR实时成像系统上实现，使该系统的成像分辨率得到明显改善。     

极化合成孔径雷达测量海浪的研究

描述了极化合成孔径雷达海浪成像过程。提出了一种极化雷达反演海浪方向谱的方法,该方法利用合成孔径雷达图像谱与海浪方向谱之间简单的线性关系和最优方法反演得到海浪方向谱,并将结果与现场资料进行了比较。经过对同一海区机载雷达P、L、C 3个波段的图像进行反演,其方向谱相当一致,而且有效波高和波向与实测数据吻合相当好。     

基于机载SAR图像的海面船只实时检测分类应用架构

合成孔径雷达(SAR)被广泛应用于军事侦察、海洋监测、灾害应急评估等各类应用中.其中,SAR海面船只检测分类是SAR海洋应用的重要一环.限于SAR特殊的成像机理,SAR图像中的目标特征多变,导致基于SAR图像的目标分类应用进展缓慢.机载SAR因其实时、便捷的部署和使用方式得到了快速发展,基于机载SAR图像的海面船只检测...     

Radar measurement of directional ocean wave spectra at low incidence angles†

Abstract

There exist several techniques for the measurement of directional ocean wave spectra. The most conventional technique is the employment of pitch-roll buoys but a disadvantage of this technique is that it measures at a fixed point. Another promising technique is the use of airborne or spaceborne radars. We present here results of a comparison between the data from an airborne radar, which is measuring near vertical incidence, and measurements of directional wave spectra obtained by means of a pitch-roll buoy and processed by using the Long-Hasselmann iterative algorithm. Although preliminary, these results constitute a step towards the employment of the airborne radar based on the Radar Ocean Wave Spectrometer (ROWS) principle as defined by Jackson (1981), as a validation tool for spaceborne synthetic aperture radars.     

适用于宽带和窄带照射源的无源合成孔径雷达成像方法

无源合成孔径雷达成像利用外部照射源和运动接收机对感兴趣场景进行成像,具有良好的电子对抗性,并可降低系统成本,利于系统小型化,缓解频带拥挤。本文给出基于逆散射理论和微局部分析的无源合成孔径成像统一理论,适用于沿任意轨迹运动的机载接收机和静止或运动的照射源。考虑发射两种发射波形：窄带连续波(Continuous-wave, CW)和宽带脉冲波形,相应给出两种新的无源合成孔径成像模式：针对宽带脉冲波形的合成孔径无源成像(Synthetic aperture hitchhiker, SAH)和针对单频或超窄带连续波的多普勒合成孔径无源成像(Doppler synthetic aperture hitchhiker, DSAH)。首先建立回波相关信号模型,该模型可消除与发射机相关的相位项,然后利用滤波反投影理论和微局部分析对相关回波数据进行反演,对应SAH和DSAH这两种无源模式,分别将相关回波数据反投影到无源距离和无源多普勒等值线上,给出详细的分辨率分析。最后通过仿真实验对成像方法进行验证。     

双峰海浪谱的SAR图像交叉谱仿真研究

由6参数双峰频谱和cos-2s型分布函数得到了双峰海浪方向谱的波数谱形式,并利用海浪谱到合成孔径雷达(Synthetic Aperture Radar,SAR)图像交叉谱的非线性转换关系,对双峰海浪谱的SAR图像交叉谱进行了仿真,分析了不同海浪参数和SAR平台参数对SAR图像交叉谱的影响,并与SAR图像谱进行了比较。     

合成孔径与实孔径雷达谱域成像算法对比分析

讨论了合成孔径雷达(Synthetic aperture radar,SAR)和实孔径雷达(Real aperture radar,RAR)一维扫描方式下的谱域成像实现问题.文中从SAR和RAR扫描下的波数域波散关系入手,分析了这两种扫描方式下的谱域填充区域和成像分辨率,指出了二者的异同,导出了相应的成像算法.单目标和组合目标的雷达成像仿真实验验证了两种扫描方式下成像算法的有效性和理论分析结果.     

Seasat detection of waves,currents and inlet discharge

Abstract

A new era of remote sensing for coastal and oceanographic monitoring was born on 26 June 1978 with the launch of Seasat. Duck-X was a 2 month experiment conducted during August to October 1978 off the east coast of the U.S.A. for the validation of the Seasat synthetic aperture radar (SAR), During this field experiment, various oceanographic phenomena were monitored. Ground truth observations of these phenomena have been correlated with Seasat SAR imagery. The ground truth sensors included airborne photographic and radar imagery, meteorological satellite imagery, land based radars, and conventional wave gauges. This paper focuses on ocean surface waves, ocean currents and coastal inlet discharge

Specifically, the direction and length of the principal ocean wave trains are compared for the periods of Seasat overflight of the Duck-X area. During these overflights significant wave heights were 1.5 m and less and the maximum wave period was 14 s. The current correlations concentrate on the western boundary of the Gulf Stream and its associated eddy structure. Inlet outflow is shown for inlets on the east coast of the U.S.A

This ground truth study has indicated that the SAR imagery contains an unanticipated abundance of information on a variety of oceanographic and coastal phenomena.     

Cover photograph Image from GOES-E spacecraft

Azimuthally travelling ocean waves are seldom well imaged by microwave real aperture radar (RAR) operating with conventional HH or VV polarizations. Attenuation of image intensity modulation in the azimuthal direction implies that ocean wave spectra derived from such images also will not be accurate. Real aperture radar cross-section modulation by long ocean waves is normally attributed to two principal sources, tilt modulation and hydrodynamic modulation. In ocean radar images both of these modulation sources are significantly attenuated in the azimuthal direction. Therefore, complete two-dimensional k-space wave spectra derived from microwave data often are quite different than physical ocean spectra. This paper uses fully-polarimetric radar measurements of ocean backscatter to identify a new source of backscatter modulation that is strongest in the azimuthal direction. This modulation source has potential for augmenting tilt and hydrodynamic modulation sources in the azimuthal direction where their weakness causes poor wave visibility. The predicted improvement in the measurement of ocean wave spectra using an optimized polarization is investigated by means of a RAR ocean imaging model. Fully-polarimetric, and conventional, radar spectrometers are proposed which are specifically optimized to sense wave-tilts in the azimuthal direction.     

Sparse synthetic aperture radar imaging with optimized azimuthal aperture

To counter the problem of acquiring and processing huge amounts of data for synthetic aperture radar(SAR)using traditional sampling techniques,a method for sparse SAR imaging with an optimized azimuthal aperture is presented.The equivalence of an azimuthal match filter and synthetic array beamforming is shown so that optimization of the azimuthal sparse aperture can be converted to optimization of synthetic array beamforming.The azimuthal sparse aperture,which is composed of a middle aperture and symmetrical bilateral apertures,can be obtained by optimization algorithms(density weighting and simulated annealing algorithms,respectively).Furthermore,sparse imaging of spectrum analysis SAR based on the optimized sparse aperture is achieved by padding zeros at null samplings and using a non-uniform Taylor window.Compared with traditional sampling,this method has the advantages of reducing the amount of sampling and alleviating the computational burden with acceptable image quality.Unlike periodic sparse sampling,the proposed method exhibits no image ghosts.The results obtained from airborne measurements demonstrate the effectiveness and superiority of the proposed method.