SAR辐射定标的融合算法研究

针对机载SAR辐射定标外场试验可重复性较差的问题,提出了一种结合内场仿真信息进行辐射定标的参数估计新算法:首先建立机载SAR定标成像模型,在进行模型有效性检验之后,利用定标成像模型得到SAR线性动态范围内定标体RCS的渐进经验分布,然后结合定标试验实测数据进行辐射定标参数的融合估计。仿真表明该算法可以减小估计结果的误差方差,提高定标精度。     

单发双收SAR 系统通用极化定标算法

单发双收极化SAR 系统只接收两个通道数据,使得极化定标可用的先验信息减少|同时由于这类系统收发极化方式的多样性(包括多种收发极化组合的双极化和简缩极化模式),目前还没有通用的定标算法。对此,该文提出了一种新的通用极化定标算法,可以广泛应用于多种收发极化组合的单发双收SAR 系统。该算法利用常见的三面角、0 二面角与45 二面角作为理想点目标,无需对目标场景和系统作假设,可以直接估计系统的发射端和接收端失真项。该文理论推导了定标算法的求解过程,仿真分析了定标器误差对失真参数估计的影响,通过点目标的定标结果和极化特征图验证了该通用定标算法的有效性。      

一种利用干涉敏感度方程的Pol-InSAR定标改进算法

目前国际上对极化SAR干涉定标技术的研究还处在理论和试验的阶段。所提出的算法存在诸多的局限性。本论文在分析极化SAR干涉系统误差源的基础上,提出了利用干涉敏感度方程的Pol-InSAR定标改进算法。该算法利用敏感度方程进行迭代参数估计,不仅提高了基线估计值的精度,而且克服了Kim等人(2000)提出的理论算法中的平地模型假设,扩大了Pol-InSAR定标算法的应用范围。最后通过模拟森林地区Pol-InSAR数据,仿真试验分析比较了改进算法与传统算法定标试验的结果,改进算法有很大的优势。     

超大阵面分布式相控阵雷达的自-交叉相位定标方法

针对传统的相控阵雷达定标算法无法适用于超大阵面分布式相控阵雷达的问题,该文提出了自定标、交叉定标相结合的相位定标算法。分析了超大阵面分布式相控阵雷达的误差来源;建立了超大阵面分布式天线阵列在工程约束下的误差模型,详细阐述了自定标和交叉定标的原理和方法,并将该方法从相位单元推广到雷达阵列。最后,对自-相交相位定标算法进行了仿真实验和工程应用。结果表明该算法能大幅提高超大阵面分布式相控阵雷达的主旁瓣电平比。      

一种基于特征点权重的机载InSAR系统区域网干涉参数定标方法

干涉参数外定标可以获取干涉相位偏置,并对干涉系统基线参数进行修正,提高干涉系统3维定位的精度。该文提出了一种新的区域网干涉参数定标算法,该方法采用特征点提取、最优相关匹配技术实现对交互连接的数据块同名点提取;利用加权联合定标技术实现少量控制点条件下干涉数据的参数定标,并对定标结果进行了理论分析。通过对具有不同地貌特征的实测机载数据的处理,验证了处理算法的有效性。     

基于粒子群优化的极化SAR定标算法

极化合成孔径雷达(SAR)的精确定标对于极化数据的终端应用至关重要。提出了一种基于粒子群优化的极化SAR定标算法,由于在估计误差参数过程中没有作任何的近似,相比于经典的极化定标算法,该方法即使在串扰参数较高时仍能保持很高的精确度。为了验证算法的有效性,分别使用仿真数据和真实的机载极化SAR数据来模拟极化失真数据,并采用多种极化定标方法对失真数据进行校准,校准结果证明了所提方法对极化误差参数有着更加稳定精确的估计。     

机载干涉SAR 区域网三维定位算法

区域网3 维定位是指同时获取多个干涉合成孔径雷达(InSAR)场景中各像素点的北向、东向和高程向的地理坐标。联合定标是区域网3 维定位的关键环节,能够保证3 维位置精度和相邻场景间的位置衔接性,并且能够在稀少控制点的条件下实现大区域多场景的3 维定位。该文提出一种适用于机载InSAR 系统的联合定标算法,该算法对多个场景的3 维位置同时定标。该算法利用最优化模型实现联合定标,并且在最优化模型中引入了权值,从而顾及到了不同质量、不同分布的控制点、同名点在联合定标中的权重差异。机载InSAR 实测数据的实验结果表明,该算法在3 维定位精度和实现过程的简洁度方面均优于传统的联合定标算法。      

一种基于Whitt算法的SAR极化定标改进方法

深入研究了Whitt等提出的基于人造点目标的极化定标算法（Whitt算法）,发现并证明了Whitt算法中对特征值对应次序的判断条件在某些情况下不成立,且分析了特征值次序对应关系错误对失真矩阵求解结果造成的影响。在此基础上,提出了新的判断条件和解决方法,对Whitt算法进行了改进。利用中国科学院电子学研究所研制的一部机载PolSAR系统进行了极化外定标实验验证,结果表明利用该改进算法进行极化定标参数求解具有更好的有效性和稳健性。     

微脉冲激光雷达探测大气气溶胶定标反演新方法

利用一种新的自适应定标反演方法在有效探测高度内确定标定值,反演微脉冲激光雷达(MPL)回波信号,并同另外一台激光雷达系统在相同时间、相同地点的探测结果进行了对比。对比结果显示利用该方法得到的结果能够同大气实际情况吻合地较好。应用该算法对连续12h的观测(共25组)数据进行批处理,结果正确反映了当时的天气状况。这说明该算法应用于MPL信号处理时具有很好的稳定性。     

基于加权最优化模型的机载InSAR联合定标算法

多个相邻场景同时进行干涉参数外定标的过程称为联合定标,联合定标能够保证相邻场景的高程衔接性,能够实现无控制点场景的干涉定标。该文提出了一种适用于机载InSAR系统的联合定标算法,该算法利用控制点和同名点信息,建立了关于待定标参数的约束方程组,并通过最优化的方法对其进行求解。同时依据各控制点和同名点处的相干系数、位置分布的不同,对各约束方程进行了加权,从而顾及到了不同质量和分布的控制点、同名点在联合定标中的权重差异。实测数据处理结果表明,该文算法优于传统的基于敏感度方程模型的联合定标算法。     

SIR-C data quality and calibration results

The SIR-C/X-SAR imaging radar took its first flight on the Space Shuttle Endeavour in April 1994 and flew for a second time in October 1994. This multifrequency radar has fully polarimetric capability at L- and C-band, and a single polarization at X-band (X-SAR). The Endeavour missions were designated the Space Radar Laboratory-1 (SRL-1) and -2 (SRL-2). Calibration of polarimetric L- and C-band data for all the different modes SIR-C offers is an especially complicated problem. The solution involves extensive analysis of pre-flight test data to come up with a model of the system, analysis of in-flight test data to determine the antenna pattern and gains of the system during operation, and analysis of data from over fourteen calibration sites distributed around the SIR-C/X-SAR orbit track. The SRL missions were the first time a multifrequency polarimetric imaging radar employing a phased array antenna has been flown in space. Calibration of SIR-C data products involved some unique technical problems given the complexity of the radar system. In this paper, the approach adopted for calibration of SIR-C data is described and the calibration performance of the data products is presented     

X-SAR radiometric calibration and data quality

In April and October, 1994 the X-SAR was flown as part of the SIR-C/X-SAR space radar laboratory missions (SRL-1/2) on the Space Shuttle. Amongst other activities DLR is responsible for the calibration of all X-SAR data products and is running the German Processing and Archiving Facility (D-PAF). Calibration activities included three major parts. Before the first mission, the authors performed a detailed analysis of the overall system to localize the main error sources and developed algorithms and procedures to correct these errors. During the missions they concentrated their efforts on calibration campaigns at the Oberpfaffenhofen super test site. Post mission activities included the determination of the antenna pattern and the absolute calibration factor as well as detailed performance analyses. This paper describes the overall approach to radiometrically calibrate the X-SAR and provides information on system performance and data quality to users in the different application fields     

Polarimetric calibration of SIR-C using point and distributedtargets

In preparation for the Shuttle Imaging Radar-C/XSAR (SIR-C/XSAR) flights, the University of Michigan has been involved in the development of calibration procedures and precision calibration devices to quantify the complex radar images with an accuracy of 0.5 dB in magnitude and 5 degrees in phase. In this paper, the preliminary results of the SIR-C calibration and a summary of the University of Michigan's activity in the Raco calibration super-site is presented. In this calibration campaign an array of point calibration targets including trihedral corner reflectors and polarimetric active radar calibrators (PARCs) in addition to a uniform distributed target were used for characterizing the radiometric calibration constant and the distortion parameters of the C-band SAR. Two different calibration methods, one based on the application of point targets and the other based on the application of the distributed target, are used to calibrate the SIR-C data and the results are compared with calibrated images provided by JPL. The distributed target used in this experiment was a field of grass, sometimes covered with snow, whose differential Mueller matrix was measured immediately after the SIR-C overpass using The University of Michigan polarimetric scatterometer systems. The scatterometers were calibrated against a precision metallic sphere and measured 100 independent spatial samples for characterizing the differential Mueller matrix of the distributed target to achieve the desired calibration accuracy. The L-band SAR has not yet been adequately calibrated for inclusion here     

Overview of results of Spaceborne Imaging Radar-C, X-Band SyntheticAperture Radar (SIR-C/X-SAR)

The Spaceborne Imaging Radar-C, X-Band Synthetic Aperture Radar (SIR-C/X-SAR) was launched on the Space Shuttle Endeavour for two ten day missions in the spring and fall of 1994. Radar data from these missions are being used to better understand the dynamic global environment. During each mission, radar images of over 300 sites around the Earth were obtained, returning over a terabit of data. SIR-C/X-SAR science investigations were focused on quantifying radar's ability to estimate surface properties of importance to understanding global change; and focused studies in geology, ecology, hydrology and oceanography, as well as radar calibration and electromagnetic theory studies. In addition, the second flight featured an interferometry experiment, where digital elevation maps were obtained by interfering data from the first and second shuttle flight, and from successive days on the second flight. SIR-C/X-SAR data have been used to validate algorithms which produce maps of vegetation type and biomass; snow, soil and vegetation moisture; and the distribution of wetlands, developed with earlier aircraft data     

Approach to derivation of SIR-C science requirements forcalibration

An attempt at determining the science requirements for polarimetric calibration for SIR-C is reported. A model describing the effect of miscalibration is presented, followed by an example showing how to assess the calibration requirements specific to an experiment. The effects of miscalibration on some commonly used polarimetric parameters are also discussed. It is shown that polarimetric calibration requirements are strongly application dependent. In consequence, the SIR-C investigators are advised to assess the calibration requirements of their own experiment. A set of numbers summarizing SIR-C polarimetric calibration goals is given     

Polarimetric calibration of the SIR-C C-band channel using activeradar calibrators and polarization selective dihedrals

A polarimetric calibration experiment of Shuttle Imaging Radar C (SIR-C) is carried out using several different calibration targets. These are C-band polarimetric active radar calibrators (PARCs), polarization selective dihedrals (PSDs), 22.5° rotated dihedrals, and a trihedral. A novel polarimetric calibration algorithm is proposed that combines existing algorithms and uses one PARC and two PSDs. An error evaluation example is shown to estimate the typical hardware error value of the calibration targets allowable for a given calibration error. The novel algorithm gives polarimetric calibration results comparable to those obtained using the existing algorithm for three PARCs. Since PSDs work at frequencies lower than design frequency, and hence can be commonly used at multiple frequency bands, the simple addition of just one more frequency band PARC allows polarimetric calibration of a dual-frequency polarimetric synthetic aperture radar (SAR) by means of the proposed algorithm     

Assessment of Atmospheric Propagation Effects in SAR Images

TerraSAR-X, the first civil German synthetic aperture radar (SAR) satellite, was successfully launched on June 15, 2007. After 4.5 days, the first processed image was obtained. The overall quality of the image was outstanding; however, suspicious features could be identified which showed precipitation-related signatures. These rain-cell signatures are thoroughly investigated, and the physical background of the related propagation effects is provided. In addition, rain-cell signatures from former missions like SIR-C/X and the Shuttle Radar Topography Mission are provided for comparison. During the commissioning phase of TerraSAR-X, a total of 12 000 scenes were investigated for potential propagation effects, and about 100 scenes revealed atmospheric effects to a visible extent. Some of the particularly interesting events were selected and are discussed in greater detail. An interesting case of data acquisition over New York will be presented, which shows typical rain-cell signatures, and the SAR image will be compared with weather-radar data acquired nearly simultaneously (within the same minute). By comparing the images, it can be clearly seen that reflectivities in the weather-radar image of 50 dBZ may cause visible artifacts in SAR images. Furthermore, in this paper, we discuss the influence of the atmosphere (troposphere) on the external calibration of TerraSAR-X. By acquiring simultaneous weather-radar data over the test site and the SAR acquisition, it was possible to flag affected SAR images and to exclude them from the procedure to derive the absolute calibration constant. Thus, it was possible to decrease the 1 sigma uncertainty of the absolute calibration factor by 0.15 dB.     

SAR内定标技术和内定标精度分析

分析了SAR内定标技术与内定标精度分析.讨论了SAR集中收发式的内定标技术,推导内定标状态下系统总功率和总功率变化量的表达式、系统增益和系统增益变化量的表达式;SAR内定标信号的处理;SAR内定标精度分析;最后完成对某地区SAR图像数据的灰度校正.     

敦煌辐射校正场地表反射率稳定性分析

辐照度基法确定卫星各波段的定标系数时,要求精确测量辐射定标场的地表反射率和漫射辐射度与总辐射度的比值。中国科学院通用光学定标与表征技术重点实验室分别于2013年6~8月及2014年8月期间,协同其他单位在敦煌校正场运用辐照度基法进行场地辐射定标,实测过程中使用ASD、SVC光谱辐射计,运用野外参考板反射率因子法确定敦煌校正场的地表反射率。详细阐述地表反射率测量方式及数据处理方法,根据实地观测数据,分析当前场区的地表反射率并与历史数据相互比对。结果显示,敦煌校正场地表反射率在时间和空间上均保持良好的稳定性。     

New Square-Root Domain Oscillators

This paper presents phase calibration technique without using any external tone for weaver image-reject receiver. Error signal (phase mismatch information) is generated using a simple algorithm and this signal is used for mismatch elimination. Calibration system has been implemented using simulink which shows an image rejection ratio of 59.5 dB can be achieved for RF signal operating at 1.8 GHz.