Theoretical Evaluation of Several Possible Along-Track InSAR Modes of TerraSAR-X for Ocean Current Measurements

The German satellite TerraSAR-X, scheduled for launch in late 2006, will permit high-resolution ocean current measurements by along-track interferometric SAR (along-track InSAR) in various experimental modes of operation, using different sections of its X-band SAR antenna array with a total length of 4.8 m as individual receive antennas. Depending on antenna and receive-chain settings, effective InSAR time lags of about 0.17 to 0.29 ms can be realized in combination with different noise levels, single-look resolutions, swath widths, and incidence angles. We give an overview of the characteristics of the possible InSAR modes and evaluate their suitability for current measurements on the basis of simulated data products. Our results indicate that the quality of interferometric stripmap data from TerraSAR-X will be clearly superior to the quality of the existing data acquired over the Dutch coast during the Shuttle Radar Topography Mission; accurate current retrievals can be expected at effective spatial resolutions on the order of 500 m. However, in modes using a multiplexed single receive chain, the effective swath width of stripmap data will be limited to only 15 km, while dual receive-chain operation offers a swath width of 30 km for stripmap data and promises a reasonable data quality even for ScanSAR data with a maximum swath width of 100 km. Finally, we consider fundamental relations between along-track baseline, instrument noise, and resulting InSAR phase noise to discuss the potential for current measuring performance improvements of TerraSAR-X follow-on satellites     

Automatic Extraction of Traffic Flows Using TerraSAR-X Along-Track Interferometry

Spaceborne synthetic aperture radar (SAR) offers great potential for the measurement of ground traffic flows. A SAR with multiple receiving apertures aligned in flight direction repeatedly images the same ground area with a short time lag. This allows for an effective detection of moving ground objects, whose range variation translates into an interferometric phase signal between the receiving channels. The high-resolution German SAR satellite TerraSAR-X offers several ways to create multiple along-track apertures. We exploit this to demonstrate satellite-based traffic-flow measurements using along-track interferometry (ATI) and Displaced Phase Center Array techniques. In this paper, we address the usage of different TerraSAR-X ATI modes for data acquisition and describe an automatic near-real-time processing chain for the extraction of traffic information. The performance of this TerraSAR-X traffic processor is significantly driven by incorporating a priori knowledge of road networks. We present examples of automatic traffic detection as well as empirical evaluations thereof using different kind of reference data.      

TerraSAR-X雷达卫星的系统特性与应用分析

TerraSAR-X是世界上首颗商用的新型高分辨雷达卫星,其成功发射和优良的数据服务引起了研究人员的广泛关注。首先介绍了TerraSAR-X雷达卫星系统的基本信息,并分析了卫星的3种成像模式及相应的特点。针对TerraSAR-x雷达卫星数据应用研究问题,给出了TerraSAR-X雷达卫星4种基本的影像数据产品的类型和特性,考察了国内外对TerraSAR-X数据应用的研究现状,并展望了其广阔的应用领域和发展潜力。     

TOPS Imaging With TerraSAR-X: Mode Design and Performance Analysis

This paper reports about the performed investigations for the implementation of the wide-swath TOPS (Terrain Observation by Progressive Scan) imaging mode with TerraSAR-X (TSX). The TOPS mode overcomes the limitations imposed by the ScanSAR mode by steering the antenna along track during the acquisition of a burst. In this way, all targets are illuminated with the complete azimuth antenna pattern, and, thus, scalloping is circumvented, and an azimuth dependence of signal-to-noise ratio and distributed target ambiguity ratio (DTAR) is avoided. However, the use of electronically steered antennas leads to a quantization of the steering law and a nonideal pattern for squinted angles (grating lobes and main lobe reduction). The former provokes spurious peaks, while the latter introduces slight scalloping and DTAR deterioration. These effects are analyzed and quantified for TSX, and a TOPS system design approach is presented. Next, the requirements concerning interferometry are investigated. Finally, several results are shown with the TSX data, including a comparison between the TOPS and the ScanSAR modes and the reporting of the first TOPS interferometric results.      

当前通信标准化工作重点技术领域分析

电信网、互联网、广电网,固定网、移动网、无线接入网等各层面的网络融合正在不断加快和走向深入,用户需求的升级和技术业务的创新改变了通信业的发展轨迹,通信技术向其他领域的渗透更加明显,通信产业和市场发展对通信标准的需求也在不断增加,需要加快标准跟踪预研和标准化工作,满足社会对标准的需求.介绍了通信技术发展现状与趋势,以及当前通信标准化面临的重点或热点领域等.     

基于一阶海洋回波的HF-SAR提取表层海流性能分析

将合成孔径技术用于高频地波雷达,以实现单站提取表层海流,对于降低观测成本、提高效率具有重要意义。但现有的高频合成孔径雷达(HF-SAR)信号模型是基于理想点目标的,而未考虑海域分辨单元的Bragg散射效应。针对这一问题,基于一阶海洋回波理论,该文提出了用HF-SAR提取表层海流的改进的信号模型,并分析了Bragg散射对HF-SAR方位向回波的影响。然后针对方位向回波信号的特点,给出了相应的速度估计算法。最后通过蒙特卡洛仿真分析了HF-SAR对指定海域分辨单元的速度估计性能,结果显示对于流速和流向的估计精度能够满足工程应用的要求,这表明用HF-SAR提取表层海流是可行的。     

Shielding of Electromagnetic Fields of Current Sources by Hemispherican Enclosures

Presented here is a theory of electromagnetic shielding of fields due to current sources by an imperfectly conducting, hemispherican, open shell with its rim in contact with a perfectly conducting ground plane. Expressions for the shielding effectiveness (SE) of the enclosure excited by Hertzian dipole sources have been derived. Numerican values of SE obtained from these expressions have been compared with those for a similarly excited imperfectly conducting spherical shell [9].     

Surface Current Source Reconstruction for Given Radiated Electromagnetic Fields

A general analytic approach is presented for reconstructing: 1) the minimum energy source enclosed by a sphere, and 2) the surface current distribution on a sphere from the knowledge of the radiated fields. The surface current source is derived by adding proper non-radiating sources to the minimum energy source. In contrast to the minimum energy volumetric distribution, the surface current derived in this paper is practically realizable. Finally, we present a closed form formula for the reconstructed spherical surface current source. We will show that this spherical surface current is indeed the unique solution of the inverse source problem for square-integrable surface electric current on a sphere in a homogenous medium.      

Application of TerraSAR-X Data for Emergent Oil-Spill Monitoring

Synthetic aperture radar (SAR) signals can propagate through hazardous weather and atmospheric conditions with heavy cloud cover, volcanic dust, snow, or rain. The all-weather capabilities of SARs have attracted significant interest in remote sensing communities, since serious environmental disasters such as oil spills have been highly “elusive” to optical sensors, making visible spectrum data vulnerable to rapidly changing atmospheric conditions. In this paper, we discuss the technical functionalities of TerraSAR-X from the emergency response perspective, describing its technical abilities in terms of a damping ratio, radiometric accuracy, and noise level with reference to the actual Hebei Spirit oil-spill incident that occurred on the west coast of the Korean peninsula in December 2007. The damping ratios estimated from the TerraSAR-X data as a function of Bragg wavenumber for various wind speeds indicate that TerraSAR-X data can be effectively used to identify oil-spill areas with acceptable accuracy. We also received ERS-2, ENVISAT, RADARSAT-1, and ALOS PALSAR data for this oil-spill event, not simultaneously but with varying time delays. The processing results for the multitemporal data sets obtained from the X- and C-band SAR systems are useful since they can be used to determine the near-real-time migration of spilt oil. The results of the current study indicate that there are distinct advantages of using X-band TerraSAR-X data for oil-spill detection compared to the data obtained at other available frequencies.      

光纤陀螺在直流及交变磁场中的磁敏感性研究

介绍了光纤陀螺的磁敏感性机理并进行了实验研究。利用亥姆霍兹线圈装置和光纤陀螺测试平台,研究了光纤陀螺在直流磁场中的磁敏感性,得到光纤陀螺数据输出与磁感应强度基本呈线性关系,以及轴向磁场和径向磁场影响系数的大小和光纤陀螺磁敏感轴的方向。主要针对50Hz的交流磁场研究交流磁场对光纤陀螺零偏和零漂的影响及其交流磁敏感性,得到交流磁场对零偏的影响可以忽略,但磁感应强度与陀螺零漂值的大小基本呈线性关系。研究了不同频率交流磁场对光纤陀螺输出的影响,说明了光纤陀螺数据输出主要与瞬态的磁感应强度成正比,不同频率交流磁场对光纤陀螺零漂值的影响不同,存在一个频率(或频率范围)对光纤陀螺零漂的影响较大,其频率范围与光纤陀螺输出带宽有关。     

Along-Track Focusing of Airborne Radar Sounding Data From West Antarctica for Improving Basal Reflection Analysis and Layer Detection

This paper presents focused synthetic aperture radar (SAR) processing of airborne radar sounding data acquired with the High-Capability Radar Sounder system at 60 MHz. The motivation is to improve basal reflection analysis for water detection and to improve layer detection and tracking. The processing and reflection analyses are applied to data from Kamb Ice Stream, West Antarctica. The SAR processor correlates the radar data with reference echoes from subsurface point targets. The references are 1-D responses limited by the pulse nadir footprint or 2-D responses that include echo tails. Unfocused SAR and incoherent integration are included for comparison. Echoes are accurately preserved from along-track slopes up to about 0.5deg for unfocused SAR, 3deg for 1-D correlations, and 10deg for 2-D correlations. The noise/clutter levels increase from unfocused SAR to 1-D and 2-D correlations, but additional gain compensates at the basal interface. The basal echo signal-to-noise ratio improvement is typically about 5 dB, and up to 10 dB for 2-D correlations in rough regions. The increased noise degrades the clarity of internal layers in the 2-D correlations, but detection of layers with slopes greater than 3deg is improved. Reflection coefficients are computed for basal water detection, and the results are compared for the different processing methods. There is a significant increase in the detected water from unfocused SAR to 1-D correlations, indicating that substantial basal water exists on moderately sloped interfaces. Very little additional water is detected from the 2-D correlations. The results from incoherent integration are close to the focused SAR results, but the noise/clutter levels are much greater.     

手征平板介质波导中的场分析

本文首次研究了手征平板介质波导中电磁波的传播特性,给出了波导中的场分布、色散关系和截止方程,以及最低截止波数Kc随手征导纳ζc的变化规律。结论表明,在手征平板介质波导中,TE、TM和TEM模均不能单独传输,其伸输模是耦合模。当ζc趋于零时,本文的所有结果均退化成通常平板介质波导情形。     

直接电流注入与自由场照射之间等价性的评估

介绍了直接电流注入技术在导弹EMC性能测试中的具体应用。文中一方面从理论上分析了直接电流注入技术及其模拟测试装置,评价了直接电流注入技术代替自由场照射的可行性;另一方面通过导弹自由场照射的理论计算及试验测试,评价了直接电流注入技术代替自由场照射的有效性。为导弹的高EMC安全裕度测试提供了一个简单、经济、有效的测试方法。     

Analytical Evaluation of Transient Magnetic Fields Due to RWG Current Bases

A new analytical approach for obtaining the time samples of the magnetic field intensity due to an impulsively excited Rao-Wilton-Glisson (RWG) basis function is presented. The approach is formulated directly in the time domain. It is shown that the magnetic field is related to the arc segments formed by the intersection of the triangular patch of the RWG basis with the sphere that is centered at the observation point and that has a radius of , where is the speed of light. In particular, the magnetic field can be expressed as the variations of two quantities with respect to . The first quantity is the arc segment length, and the second quantity is the bisecting vector of the arc segment. Analytical representations of these quantities are presented. Contrary to previous studies, these representations do not require the calculation of the intersection points of the sphere with the boundaries of the bases. The validity of the obtained time domain formulae is demonstrated through comparison of the results with those obtained in the frequency domain by using numerical quadrature. Finally, it is demonstrated that the derived formulae yield closed-form expressions when convolved with piecewise polynomial temporal basis functions.     

Investigation of Ocean Surface Wave Refraction Using TerraSAR-X Data

As a scientific and technological continuation of the X-band Synthetic Aperture Radar (X-SAR) and Shuttle Radar Topography Mission (SRTM) missions, the new X-SAR, namely, TerraSAR-X (TSX), was launched on June 15, 2007. Since then, it has provided numerous high-quality data over land and ocean operationally. In this paper, surface wave refraction and diffraction are investigated using TSX imagery acquired over the coast of Terceira island situated in the North Atlantic. Peak wavelength and wave direction are determined by SAR 2-D image spectra. They are compared to measurements of X-band marine radar and results of the WAve prediction Model (WAM). Significant wave height in the near-shore shallow water region is estimated from TSX Spotlight mode data following the wave refraction laws and using the developed XWAVE empirical algorithm. Image spectra of the TSX subscenes in the full-coverage region are given to investigate significant changes of wave direction and length. By analyzing another TSX image acquired in StripMap mode, a shadow zone in the lee side of Terceira island is identified. It is influenced jointly by wave refraction and diffraction. Furthermore, a cross-sea pattern revealed in the image spectra is investigated. The cross sea is generated by the diffracted wave rays from the northern and southern coasts of the island. Less wave directional spreading for the cross-sea situation is observed as well when compared to the image spectra at the origin of diffraction.      

电磁场问题的“场”理论与“路”理论

基于Maxwell方程组的电磁场理论（“场”理论）和基于基尔霍夫定律的集总参数电路理论，以及基于电报方程的分布参数电路理论（“路”理论）是求解电磁场问题的主要理论工具。文中详细讨论了这三种理论间的关系，给出了应用“路”理论简化电磁场问题分析的几个典型例子，并讨论了应用“路”理论分析“场”问题的局限性和相关注意事项。     

分布式小卫星系统沿航迹干涉SAR测速去模糊方法

本文结合分布式小卫星系统的多基线结构阐述了沿航迹干涉SAR(Along-Track Interferometric SAR)测速的解模糊问题,提出利用多个卫星的干涉相位信息去除沿航迹干涉SAR的测速模糊。以往单颗卫星作SAR-GMTI时,用固定长度基线的双天线作动目标检测总会遇到速度模糊问题,而此问题在分布式系统中多基线组合情况下则迎刃而解。本文还分析了小卫星编队立体队形及地球自转等因素下的动目标测速去模糊。     

一种新的机载条带式SAR沿航向运动补偿方法

提出了一种新的机载条带式SAR沿航向运动误差的补偿方法.它不用插值,所以节省了运算量、避免了插值带来的图像质量下降,因而对机载SAR系统的实时成像有好的应用前景.理论分析、仿真和实测数据成像证明了该方法的正确性和有效性.     

并矢分析在电磁场求解中的应用

给出广义电磁场矢量和并矢波动方程的格林函数积分解,在物理定律和边界条件的约束下,用并矢分析的方法证明了两解的同解性,并对自由空间并矢格林函数的对称性进行了并矢分析展开验证。结合并矢分析法求解电磁场的两个应用实例,表明并矢分析法相对于传统方法具有简捷明了的特性。