星载微波散射计的在轨定标技术现状及展望

星载微波散射计通过测量海面不同方位向的后向散射系数反演出海面的风速和风向,为了满足测量精度要求,必须对其进行在轨定标.本文总结了现有微波散射计的在轨定标技术,包括有源定标器法、陆地自然目标法、海洋目标法和星星交叉定标法;然后分析了每种定标方法的优缺点;最后,描述了现有定标方法适用扇形波束体制散射计和笔形波束圆锥扫描体制散射计的特性.     

星载雷达高度计沙漠散射特性及定标方法研究

为了提高星载雷达高度计海面风速产品的精度并更好地修正海况偏差的影响,有必要对高度计测量的后向散射系数进行定标。分布目标是星载雷达散射系数定标的有效手段,而沙漠的散射特性特别适于高度计的散射系数定标。检验了Jason-2卫星高度计的沙漠回波波形,在澳大利亚辛普森沙漠和我国的塔克拉玛干沙漠选取了适当的区域,收集了在这些区域长达7a的Jason-2高度计数据。基于这些数据,研究了Jason-2卫星雷达高度计在沙漠上的散射系数特性,并提出了基于沙漠的散射系数定标方法,分析了其原理、可行性和试验方案,探讨了高度计和现场定标散射计足迹匹配等关键技术,并对其定标误差进行了分析,论证了沙漠定标场可实现优于0.5dB的定标精度。该方法有助于进一步提升海洋2号(HY-2A)卫星风速和海况偏差产品的质量和应用前景。     

基于星载旋转扫描雷达的高分辨率实现

为了提高传统星载真实孔径雷达(微波散射计)空间分辨率、满足地球物理参数(雪水当量、冰雪冻融等)的观测需求,开展了扫描体制散射计的高分辨率分析和研究。基于距离向脉冲压缩处理和方位向多普勒处理技术,提出了一种旋转扫描体制下的分辨率提高方法。针对笔形波束圆锥扫描散射计的观测方位角在天线扫描过程中不断变化的特点,在正侧视和斜侧视时对模型分别进行了仿真验证。验证表明利用散射计旋转扫描多普勒信息能够建立与方位向分辨率的关系,可以有效提高微波散射计的空间分辨率。当正侧视时,方位向分辨率可以达到2km,斜前视或者斜后视时,方位向分辨率能够达到2~5km。针对雪水当量模型数据进行分析验证,设计的系统传递误差Kpc在5km分辨率下可以达到0.3,在2km分辨率下达到0.3~0.5。     

利用微波散射估计海面气体传输速度*

把作者提出的水气界面处气体传输率复合计算公式及适用于不同频率的微波散射反演公式〔1〕结合起来,探索根据微波散射直接反演水气界面处气体传输率的可行性。介绍了根据此反演方法所作的预测与Wanninkhof和Bliven〔2〕在Delft大学100 m长风水槽进行的微波散射和气体传输同步测量结果所进行的比较,比较结果是令人满意的。这表明:从微波散射系数反演水气界面风速,进而推求水气界面处气体传输速度是全球尺度遥测估计水气界面气体传输的一条很有希望的途径。在此采用的反演计算方法较之直接关联遥感据与传输速度的预测方法更有其普遍性和灵活性,即它不依赖散射计工作频率,同时还可依据不同的气体传输测量数据来源不断改进反演公式。     

星载微波散射计高分辨率σ~0图像重构方法研究

针对我国海洋二号卫星微波散射计(HaiYang-2Scatterometer,HY2-SCAT)数据存在的空间分辨率较低、无法满足对于地球冰冻圈、生物圈探测需求的问题,以其数据拓展应用为目标,开展了微波散射计高分辨率后向散射系数(σ0)图像重构技术仿真研究。采用仿真的方法实现并对比了AART(Additive Algebraic Reconstruction Technique)、MART(Multiplicative Algebraic Reconstruction Technique)、SIR(Scatterometer Image Reconstruction)3种分辨率增强的图像重构算法,得出了AART算法没有噪声抑制能力、MART算法噪声抑制能力较弱、SIR算法具有较强的噪声抑制能力,能更好地重构图像,达到分辨率增强效果的结论。然后采用HY2-SCAT测量L1B数据对结论进行了验证,重构了岛屿的地貌特征,得到了分辨率增强、细节丰富、边界清晰的重构图像;重构后的图像还可以应用于植被、冰盖和台风观测等地球地理学研究领域。     

后向散射系数的贝叶斯估计

后向散射系数是合成孔径雷达图像中重要的物理参数.由于合成孔径雷达测量系统的噪声干扰和其他不确定因素影响使得测量数据往往不够精确,这就需要对测量数据进行合理估计.为了对后向散射系数做出准确合理的估计,文章将后向散射系数的先验知识考虑进去,给出了后向散射系数的三种贝叶斯估计算法.贝叶斯估计的关键是概率密度模型的选取.例中选用贝塔(Beta)分布作为先验概率密度模型,伽玛(Gamma)分布作为条件概率密度模型得到了合理的估计结果,并与最大似然估计(ML)算法进行了比较,比较结果表明在对后向散射系数的估计中,贝叶斯估计算法要明显优于最大似然估计算法.     

2～18GHz外场RCS测量系统的设计与实现

外场RCS测量是获取大型全尺寸目标电磁散射特性的重要手段。在介绍脉间频率步进雷达一维、二维成像原理的基础上,给出了一种宽带(2～18GHz)双通道雷达目标RCS测量系统的设计与实现。该系统可用于外场目标后向电磁散射特性测量和散射源高分辨力二维成像。介绍了系统的技术特点,讨论了影响外场RCS测量精度的几种主要误差来源并提出了解决办法,最后对系统性能进行了验证。     

神舟4号多模态微波遥感器散射计分系统

介绍神舟4号多模态微波遥感器散射计分系统的研制情况和在轨实验情况。首先简单介绍了系统组成、工作特点以及机载校飞实验, 随后介绍了数据处理过程以及遥感器地面信号处理系统的研制开发工作, 给出了在轨海面风场测量的实验结果以及亚马逊热带雨林的后向散射系数测量结果。     

海面微波散射系数的一个工程算法

介绍了一个基于徽波散射双尺度模型的散射来数工程计葬方法，根据AAFE的机载雷达散射计数据，拟合确定了计葬公式所需参数。该算法可以反映散射系数迎、顺风不对称性的重要特征。计葬的精度和效果与现有的若干方法相比也是令人满意的。     

基于多次散射目标模型的雷达成像研究

合成孔径雷达（Synthetic Aperture Radar, SAR）作为一种主动微波传感器,被广泛应用于遥感对地观测。然而,传统上的雷达散射模型是基于几何光学近似的,忽略了地物目标之间的相互作用,即多次散射效应。为了充分挖掘和利用毫米波雷达影像中目标电磁散射特性信息,亟需对典型目标的多次散射效应进行建模仿真和验证。基于矩量法（Method of Moments, MoM）分析了球体、二面角等目标表面等效电流分布与分段成像结果的对应关系,并利用后向投影（Back-Projection, BP）算法进行电磁仿真成像,总结了单/双基地雷达模式对成像中散射机制的影响。结果表明：目标表面等效电流分布以及分段等效合成孔径张角会随入射角度发生改变,其中分段等效合成孔径张角会影响方位向分辨率;双基地雷达成像结果中包含更丰富的电磁散射信息。本研究可为SAR系统设计和验证、典型目标回波特性数据收集以及如何基于高解析度SAR影像进行目标识别等研究提供借鉴与参考。     

包敦其河冲积扇全极化SAR数据同极化相关特征分析

冲积扇蕴涵气候演变信息,极化合成孔径雷达（Polarimetric Synthetic Aperture Radar-PolSAR）能够获取丰富的地表信息,更有效地提取冲积扇所在地区气候演变过程。不同极化正交基对应的同极化相关特征是反映地物特征的重要参数之一,其绝对值为同极化相关系数,辐角为相位差。利用全极化SIR-C L波段数据,提取并分析包敦其河冲积扇不同极化正交基对应的同极化相关特征,发现水平-垂直（h,v）线性正交基对应的同极化相关特征能够有效地反映该冲积扇的不同特征区域。此外,对同极化相关特征随包敦其河冲积扇地表粗糙度以及湿度的变化规律进行统计分析,结果表明（h,v）线性正交基对应的同极化相位差以及右旋-左旋（r,l）极化正交基对应的同极化相关系数对地表参数敏感,能够描述包敦其河冲积扇地表参数的变化。     

Multiband-scatterometer data analysis of forests

Abstract

The airborne multiband scatterometer DUTSCAT promises to become a useful tool for research in the field of active microwave remote sensing. The system can measure accurate σ ° values in six frequency bands simultaneously at a selected incidence angle and polarization. An evaluation of the use of this system for research in forestry, in particular the problems related with probing thick vegetation canopies, is given. The system can acquire information on the vertical distribution of backscattering. Through inversion of a multilevel model, σ ° of forests can be divided in contributions from a number of arbitrarily chosen layers ( three or four). A simple and accurate new approach for the computation of cc values for forests (or other thick vegetation covers) from scatterometer data is given and compared with the less accurate ‘ standard’ way of processing used for other types of targets.     

用最小回路求两个简单多边形的交、并、差集

针对求两个简单多边形交、并、差集问题,提出一种基于最小回路的新算法。首先,将初始多边形P和Q初始化为逆时针方向,并将两个多边形交点处的关联边排序。然后,从各个交点出发利用最小转角法搜索最小回路,并根据这些最小回路中包含P和Q边的方向性对它们进行分类。最终,不同类别的最小回路将对应P和Q的交、并、差集。算法的时间复杂度为O((n+m+k)logd),其中n、m 分别是P和Q的顶点数,k是两多边形的交点数,d为将多边形分割的单调链数。算法几何意义明显,对于多边形布尔运算中的重合顶点、重合边等奇异情形,具有较好的适应性。     

Influence factors of sparse microwave imaging radar system performance:approaches to waveform design and platform motion analysis

Sparse microwave imaging radar is a newly developed concept of microwave imaging system,which tries to combine the traditional radar imaging system with sparse signal processing theories,achieving the aim of reducing the complexity of microwave imaging systems and enhancing the system performance.In this paper,we introduce some basic concepts of sparse signal processing theory,and then apply it to the traditional radar imaging system to get the mathematical model of sparse microwave imaging system.We analyze the factors that determine the performance of sparse microwave imaging radar,including scene,waveform and platform.According to the radar model,we analyze how these factors influence the radar system and how to optimize them.Simulation results of the sparse microwave imaging radar system are also provided.     

HY-2 雷达高度计和微波散射计

海洋动力环境卫星(HY22) 是一种获取海洋动力环境信息的专用对地遥感卫星, 计划中的我国第一颗海洋动力环境卫星(HY22A ) 以微波遥感器为主, 包括一台雷达高度计、一台微波散射计和一台多通道微波辐射计。介绍HY22 雷达高度计和微波散射计的系统设计和主要技术指标。
     

基于互测BGM的系统级故障诊断集团算法

本文提出了基于互测BGM故障模型的系统级故障诊断集团算法的理论,定义了绝对故障和最终诊断图,由此能找到所有基于互测BGM故障模型的相容故障模式,即使不满足t 可诊断性,也大大减少了系统级故障诊断的复杂度,尤其是对强t 可诊断系统。     

Preliminary analysis of ERS-1 wind scatterometer data over land surfaces

This Letter presents preliminary observations made with the ERS-1 wind scatterometer over land surfaces. A global backscattering coefficient image, synthesized from the original raw data indicates a strong correlation between the radar signal and the distribution of the main vegetation types throughout the world. In particular, tropical vegetation formations are well identified. The effects of angular and multitemporal variations on the backscattering coefficient σ⁰ are shown for different terrestrial surfaces. Illustrations are given for the African continent which presents numerous vegetation types along a north-south latitudinal gradient. Results indicate the strong capability of the ERS-1 scatterometer to discriminate and monitor vegetation change at a global scale.     

Semi-empirical calibration of the IEM backscattering model using radar images and moisture and roughness field measurements

Estimating surface parameters by radar-image inversion requires the use of well-calibrated backscattering models. None of the existing models is capable of correctly simulating scatterometer or satellite radar data. We propose a semi-empirical calibration of the Integral Equation Model (IEM) backscattering model in order to better reproduce the radar backscattering coefficient over bare agricultural soils. As correlation length is not only the least accurate but also the most difficult to measure of the parameters required in the models, we propose that it be replaced by a calibration parameter that would be estimated empirically from experimental databases of radar images and field measurements. This calibration was carried out using a number of radar configurations with different incidence angles, polarization configurations, and radar frequencies. Using several databases, the relationship between the calibration parameter and the surface roughness was determined for each radar configuration. In addition, the effect of the correlation function shape on IEM performance was studied using the three correlation functions (exponential, fractal, and Gaussian). The calibrated version of the IEM was then validated using another independent set of experimental data. The results show good agreement between the backscattering coefficient provided by the radar systems and that simulated by the calibrated version of the IEM. This calibrated version of the IEM can be used in inversion procedures to retrieve surface roughness and/or moisture values from radar images.     

Sparse microwave imaging:Principles and applications

This paper provides principles and applications of the sparse microwave imaging theory and technology.Synthetic aperture radar(SAR) is an important method of modern remote sensing.During decades microwave imaging technology has achieved remarkable progress in the system performance of microwave imaging technology,and at the same time encountered increasing complexity in system implementation.The sparse microwave imaging introduces the sparse signal processing theory to radar imaging to obtain new theory,new system and new methodology of microwave imaging.Based on classical SAR imaging model and fundamental theories of sparse signal processing,we can derive the model of sparse microwave imaging,which is a sparse measurement and recovery problem and can be solved with various algorithms.There exist several fundamental points that must be considered in the efforts of applying sparse signal processing to radar imaging,including sparse representation,measurement matrix construction,unambiguity reconstruction and performance evaluation.Based on these considerations,the sparse signal processing could be successfully applied to radar imaging,and achieve benefits in several aspects,including improvement of image quality,reduction of data amount for sparse scene and enhancement of system performance.The sparse signal processing has also been applied in several specific radar imaging applications.