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     

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     

Polarimetric SAR calibration experiment using active radarcalibrators

Active radar calibrators are used to derive both the amplitude and phase characteristics of a multichannel polarimetric synthetic aperture radar (SAR) from the complex image data. Results are presented from an experiment carried out using the NASA/JPL DC-8 aircraft SAR over a calibration site at Goldstone, California. As part of the experiment, polarimetric active radar calibrators (PARCs) with adjustable polarization signatures were deployed. Experimental results demonstrate that the PARCs can be used to calibrate polarimetric SAR images successfully. Restrictions on the application of the PARC calibration procedure are discussed     

新型C频段TE21模圆极化合成网络设计

指出了波导结构及微带形式的TE21模圆极化合成网络的不足,介绍了3 dB分支定向耦舍器的基本原理,设计了新型C频段空气带状线形式的圆极化合成网络,并对该结构进行仿真和测试,结果满足性能要求.此种合成网络可与耦合器设计为一体,既可以增加结构强度,还缩短了传输路径,降低了损耗,目前已经成功应用在多种型号天线系统上.     

Spectral and polarization selective fiber-optic elements

A pair of coupled step-index waveguides is analyzed. Characteristic equations are obtained and used to evaluate the cutoff frequencies and coupling constants. Mode transformation at tapers is analyzed. The spectral properties of fused couplers and tapered filters for which cutoff frequencies of higher modes were observed are studied. A fiber polarization splitter is realized. A semiconductor laser with an external dispersive cavity based on the spectral selective coupler is designed     

双通道跟踪接收机的动态极化校相

传统校相方法无法检测双通道单脉冲体制雷达极化失配问题.采用基于静态目标的动态极化校相方法,即在静态条件下,增加一个信标天线正交极化角校相环节,用于完成跟踪接收机和差信道的校相工作.数学模型的构建、仿真计算以及实测结果均表明,采用该方法可以准确识别双通道单脉冲体制雷达双通道极化失配问题,弥补了传统校相方法在检测跟踪接收机和差信道极化失配问题上的缺陷.     

改善单偏置天线交叉极化劣化的C-band馈源

描述了用波纹喇叭中的 HE_(21)模抵消单偏置抛物面天线非对称平面交叉极化分量的基本原理,介绍了 TE_(21) 模激励器、波纹喇叭的设计方法和展宽馈源抑制单偏置天线交叉极化分量频带宽度的设计方法,给出了 C 波段 2．4m 单偏置抛物面天线的实验测试数据,单偏置抛物面天线非对称平面交叉极化电平改善了10dB,抑制交叉极化分量的馈源相对工作频带宽度大于8％。这种 TE_(21)模激励技术和与主模 TE_(11)模相位差的调整方法,对馈源的电压驻波比几乎没有影响。     

Game theory and the frequency selective interference channel

As discussed in this paper, the frequency selective interference channel is important, both from a practical as from an information theoretic point of view. We show that it has many intriguing aspects from a game theoretic point of view as well, and that various levels of interference admit different types of game theoretic techniques.     

超宽带信道的频域测量及校准

介绍了超宽带频域信道测量的方法,分析了降低测量数据准确度的因素,提出了新的校准测量方法。基于收发天线的系统传输函数,讨论了超宽带天线方向角的变化对波形畸变的影响。在暗室中采用矢量网络分析仪,测量收发天线之间不同方位角的频域传输函数,测量频率范围为0.5 GHz至16 GHz,通过频域复数除法及加权平均,消除天线等测量硬件的误差影响。将该校准测量方案运用于车载超宽带信道的测量与建模中,获得了准确的小尺度衰落信道参数。     

Preliminary observations of volcanoes with the SIR-C radar

The two flights of the Shuttle Imaging Radar (SIR-C/X-SAR) in April and October 1994 provided a wealth of new image data over many of the world's volcanoes, including 13 of the 15 International Decade Volcanoes. A first look at these data shows that mapping of remote volcanoes (e.g., Nyiragongo and Nyamuragira in Africa) will now be easier, especially when aided by the collection of multi-parameter radar data over better known analogous volcanoes such as Kilauea, HI. The utility of the radar to identify different types of lava flows is shown for Fernandina volcano, Galapagos Islands. Growth of mudflow deposits (“lahars”) that were emplaced on Mount Pinatubo, Philippines, during the six months between the two missions is also illustrated. Additionally, interferometric radar data were collected over several active volcanoes; the potential uses of these data for topographic mapping and ground deformation studies are discussed     

Simulations of the time and frequency selective outdoor mobileradio channel

A prerequisite for the performance analysis and optimization of new mobile communication systems is a model for the channel behavior. Channel fading simulation based on the model is generally chosen for flexible validation, testing, and comparison of new designs. To simulate the time- and frequency-selective behavior of macrocell mobile radio channels, a method is presented, which is based on a physical model for the radiowave propagation process in these environments. The approach enables a generation of complex impulse responses as given by the statistics of the underlying channel behavior. Delay profiles and fading characteristics of the multipath structures can be efficiently simulated by reproducing the physical wave interference process, thereby incorporating the different channel characteristics that are observed in different environments, such as urban or suburban areas. The accuracy of the method is demonstrated by comparison of simulated results with the equivalent measured functions     

极化码在AWGN信道下的性能分析

首先介绍了信道编码技术对于5G各方面的重要性,其次对极化码的基本原理进行阐述,尤其对信道极化部分进行了详细阐述,对编译码方法进行阐述,重点阐述使用SC(连续消除)译码算法编写程序在AWGN(高斯信道)中进行仿真,最后对仿真结果进行分析,得出信噪比对误码率的影响,通过这些仿真结果可见信道编码可以提高信道的可靠性和网络性能,而这正是在未来5G通信中需要达到的效果。     

Polarimetric channel characterization of foliage for performanceassessment of GPS receivers under tree canopies

The attenuation, depolarization, and fluctuation of a microwave signal going through a tree canopy are investigated by developing a Monte Carlo based coherent scattering model. In particular, the model is used to analyze the performance of Global Positioning System (GPS) receivers under tree canopies. Also the frequency and time-domain channel characteristics of a forest are investigated when a transmitter is outside and a receiver is inside a forest. A fractal algorithm (Lindenmayer system) is used to generate the structure of coniferous or deciduous trees whose basic building blocks are arbitrarily oriented finite cylinders, thin dielectric needles, and thin dielectric disks. Attenuation and phase change of the mean field through foliage is accounted for using Foldy's approximation. Scattering of the mean field from individual tree components and their images in the underlying ground plane are computed analytically and added coherently. Since tree trunks and some branches are large compared to the wavelength and may be in the close proximity of the receiver, a closed-form and uniform expression for the scattered near-field from dielectric cylinders is also developed. Monte Carlo simulation of field calculation is applied to a cluster of trees in order to estimate the statistics of the channel parameters, such as the probability density function (pdf) of the polarization state of the transmitted field, path loss, and the incoherent scattered power (the second moment of the scattered field), as a function of the observation point above the ground     

CLASSIFICATION OF MULTI-LOOK POLARIMETRIC SAR IMAGERY AND POLARIZATION CHANNEL OPTIMIZATION

In this paper, a new maximum likelihood (ML) classification algorithm is proposed to classify the multi-look polarimetric synthetic aperture radar (SAR) imagery. Experimental results with the NASA/JPL airborne L-band polarimetric SAR data demonstrate the effectiveness of the new algorithm. Furthermore, when using the algorithm in the classifications with subsets of the multi-look polarimetric SAR data, the polarization-channel optimization for the terrain type classification is implemented.     

通道误差对时频-MUSIC算法性能的影响和校正

提出了修正空间时频分布(STFD)矩阵的到达角(DOA)估计算法,该算法可实现对宽带线性调频信号的DOA估计;分析了通道不一致对算法性能的影响,建立了宽带信号模型的通道误差模型;给出了均匀直线阵列(ULA)情况下通道不一致的无源校正算法,该算法通过先粗测信号DOA,据此将修正STFD矩阵进行变换,变换后矩阵具有Toeplitz结构,通过恢复其Toeplitz结构来实现通道误差校正.     

Generation of digital elevation models by using SIR-C/X-SARmultifrequency two-pass interferometry: the Etna case study

The authors exploit the interferometric multifrequency potentiality of the SIR-C/X-SAR system which is equipped with an L-, C-, and X-band sensor. They present a solution to improve the unwrapping performance of the C- and X-band data by considering the L-band unwrapped pattern. A new algorithm for the generation of a single digital elevation model (DEM) combining L-, C-, and X-band information is presented. This solution is based on the fusion of the unwrapped phase patterns by using a Kalman filter. The proposed fusion operation also accounts for the coherence characteristics of the three data sets. The selected test site is the Mt. Etna region in Italy which is very interesting from the volcanological and geological point of view. Numerical assessments of the achieved results are provided by evaluating the height accuracy with respect to a reference DEM     

偏振探测系统的摄像机标定与图像畸变校正研究

偏振探测在许多相关领域的应用日益广泛,探测系统的标定及校准是精确提取被探目标的前提.本文针对偏振探测系统,分析了基于2D平面标靶的摄像机标定算法,建立了摄像机线性模型和非线性畸变模型,通过线性及非线性结合的算法,得到了精确的摄像机内外部参数.利用镜头的畸变模型,提出了一种采用牛顿迭代算法来求解高阶非线性方程组对图像畸变校正的方法,建立了各像素点畸变量与到畸变中心距离的关系,最后对畸变校正前后的图像进行了测试实验,测试结果表明:测试点实际畸变大小符合理论畸变量关系,很好地验证了镜头的径向畸变特性;经畸变校正后的偏振图像能有效提高被探目标提取的准确率,偏振图像的畸变校正对复杂背景下目标提取准确率的影响最明显.     

Two-dimensional angle and polarization estimation using the ESPRITalgorithm

It is shown how the ESPRIT (estimation of signal parameters via rotational invariance techniques) algorithm may be used with a square array of crossed dipoles to estimate both the two-dimensional arrival angles and the polarization of incoming narrowband signals. The ESPRIT algorithm exploits the invariance properties of such an array so that both angle and polarization estimates may be computed. Some typical examples showing the use of this approach are presented     

GF5B热红外通道星上定标与验证

以GF5B卫星发射前实验室定标为基础,采用星上0级黑体定标数据,建立了适用于GF5B热红外通道的星上绝对辐射定标模型。通过对2022年01月12日星上黑体定标数据进行处理,获得成像仪热红外通道的绝对辐射定标系数。对星上定标系统精度进行分析,并采用地面同步烟台浮标数据对定标结果进行精度验证,结果表明,在轨后星上定标系统的绝对定标精度为0.9 K;星地验证结果显示B11和B12通道亮温的偏差分别为0.33、0.77 K。说明基于星上黑体的定标方法具有较好的精度,定标结果可靠,可满足遥感数据定量化应用的需要,为实时准确获取热红外通道定标系数提供了方法借鉴。