针对C波段组网SAR卫星的风场优化反演方法研究

地球物理模型函数是一种常被用于同极化合成孔径雷达(synthetic aperture radar,SAR)的风场反演方法.在使用该方法提取SAR数据的风速时,需要将风向作为输入信息,这导致反演风速的精度受风向精度的影响,且使SAR风场反演无法独立完成.为了解决这些问题,通过数值模拟获取仿真的组网SAR卫星数据,3颗S...     

基于准线性近似方法的SAR图像海浪参数反演研究

本文根据相干斑噪声的时间快变特征和非海浪纹理现象的时间缓变特征，基于交叉谱提出了一种对相干斑噪声和大尺度非海浪纹理的抑制的方法，进而结合SAR图像谱和海浪谱之间的准线性映射关系，基于SAR数据对海浪参数进行了反演。在反演过程中，首先仿真分析了不同海况下准线性近似法的海浪反演能力，结果表明：风浪引起的方位向截断效应会显著影响反演精度，因此该方法在低风速时的涌浪反演精度更高。通过将基于Sentinel-1卫星2020年的波模式SAR数据的反演结果与欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts, ECMWF)提供的再分析数据进行对比，发现高海况海浪有效波高反演结果明显偏低，而且该反演误差与风速、方位向截断波长之间存在显著相关性。为了提高有效波高的反演精度，本文进一步给出了海浪有效波高反演误差与风速、方位向截断波长之间的经验校正函数模型，结果显示，通过该模型修正后的海浪有效波高反演结果与ECMWF数据和浮标测量数据具有良好一致性。     

星载合成孔径雷达图像反演海面风场方法综述

合成孔径雷达作为微波雷达,具有全天候、全天时、高分辨率对海面成像的能力,能实现多波段、多极化、多视角的观测海面,可以提供大范围、高精度的实时动态海面信息,对其进行深入研究有着重要的意义。基于合成孔径雷达图像,分别以风向和风速反演为主线,对国内外海面风场反演的工作进行了详细的总结。     

基于SAR海浪方向谱的中国海海浪特性研究

基于Hasselmanns提出的SAR反演海浪方向谱的MPI算法,对2003-2012年间的中国海Envisat ASAR波模式数据进行了海浪方向谱反演。统计由反演的海浪方向谱得到的海浪有效波高数据,依据海浪浪级的划分,分析了中国海海浪浪级的分布特点,获得一些有参考价值的结果:(1)中国海3-4级海况的年出现概率最高,达85%;(2)中国海累月不同浪级的海浪出现概率分布符合高斯分布函数:f(x)=a*exp(-((x-1-b)/c)^2);(3)分析上述高斯分布函数的拟合系数a、b、c,发现其分布也有一定规律性。同时应用反演得到的海浪有效波高、平均波周期、平均波向等数据,分析了中国海的海浪时空分布特性,得到一些可供参考的结果。     

基于极化SAR数据的海浪信息反演

基于C波段极化AIRSAR数据,采用性能较好、计算简便的圆极化法提取极化方位角,利用极化SAR数据的反演算法反演海浪参数。将反演的海浪参数与NDBC浮标测得数据进行比对,结果显示两者反演海浪参数较为一致,精度符合海浪观测要求。同时,对海岸岬角在海浪传播过程中的折射作用进行了分析,发现海浪由开放水域向近岸浅水域传播过程中受到海岸岬角折射影响较大,结果符合近岸海浪传播特征。     

合成孔径雷达影像反演台风浪的研究

台风浪的研究对于船舶航行、避风以及港口、海洋和近岸建筑物的安全有着重要的现实意义.本文选用台风“莫拉克”(MORAKOT)发生时的ERS-2卫星的合成孔径雷达(SAR)海面影像为例进行了相关研究,采用遥感软件和Matlab编程相结合,得到了台风浪的主波波长、波向和周期.与同实测资料吻合较好的Mike21软件的数值模拟结果相比较,效果良好.     

卫星SAR图像的海洋大气边界层特征参数的反演

针对中国南海ERS-2／SAR三维对流涡旋图像,分别利用Young的协方差方法和惯性子域方法,反演了对流海洋大气边界层高度、海洋大气边界层垂直对流尺度速度、表面浮力通量、Obukhov长度、稳定性校正后的海面风速和海面风速稳定性校正因子。结果表明,2种反演方法的结果符合较好,在一定程度上说明利用协方差方法和惯性子域方法从卫星SAR图像反演海洋大气边界层参数的有效性。     

基于微波多载荷优势互补的海面风场联合反演方法研究

海面风场的遥感探测主要通过合成孔径雷达（Synthetic Aperture Radar,SAR）和微波散射计等微波遥感器进行,近年来波谱仪也可用来探测风场信息。各遥感器独立工作,具有不同的入射角、覆盖范围和分辨率,在风场探测方面各有其优势和局限性。本文基于各类微波遥感器独特的观测方式,根据各自的时空匹配规则,相互借助实现3种载荷的两两联合,波谱仪和散射计分别与SAR联合为其提供风向并得到SAR的风速结果,与ERA5的均方根误差分别为1.972 7 m/s和1.986 0 m/s,散射计与波谱仪相互联合为波谱仪去除风向模糊,去模糊的风向结果为26.758 9°,都符合目前风场反演公认的标准,风速和风向的均方根误差小于2 m/s和30°。本文解决了现阶段单模式观测风场的缺陷,为我国未来发射SAR、散射计、波谱仪多载荷卫星的风场反演提供互补信息的支持,为实现多载荷区域大范围高精度风场研究做准备。     

高分辨率全极化SAR水上桥梁参数反演

高分辨率SAR中,桥梁的各次反射回波表现为条带状,这给桥梁参数的反演带来了困难。本文提出了一种适用于高分辨率全极化SAR的水上桥梁参数反演方法。首先,通过极化散射特征区分出桥梁的单次、二次和三次反射回波目标。然后,结合微波反射和折射的原理,分析了高分辨SAR图像中桥梁的各次反射回波成条带状的原因,在此基础上提出了各次回波目标的提取方法和桥梁参数反演方法。最后,利用获取的AIRSAR数据反演了桥梁的上下桥高、桥厚、桥宽、桥长及桥塔高度等参数,通过与实测数据对比,结果表明,本文的方法能较准确地反演桥梁的各项参数,其中桥高误差仅为1.3%,结果也表明了在高分辨率条件下,C和L波段的桥梁参数反演能力相当。     

降雨对SAR风场反演的影响及校正

合成孔径雷达（Synthetic Aperture Radar, SAR）在风场反演中发挥着重要的作用,但由于受到降雨的影响,海面风场的反演精度会随之下降。本文利用Radarsat-2 SAR观测数据,准同步降雨数据和再分析风场资料对2014年台风"威马逊"外围风场受降雨影响的情况进行了分析,建立了雨致海表阻尼后向散射系数受降雨强度,入射角等因素影响的拟合模型,并对降雨引起的信号衰减,后向体散射进行了评估。实验发现雨致海表面阻尼作用抑制风致海面波的影响十分明显,且降雨造成的信号衰减随降雨强度和入射角的增大而增加,雨滴产生的后向体散射和雨致海表阻尼作用造成的后向散射系数变化随降雨强度的增大而增加,随入射角的增大而减小。实例表明本文建立的模型能够有效改善降雨条件下SAR风场的反演精度。     

全极化合成孔径雷达近岸风场反演研究

Coastal winds are strongly influenced by topology and discontinuity between land and sea surfaces. Wind assessment from remote sensing in such a complex area remains a challenge. Space-borne scatterometer does not provide any information about the coastal wind field, as the coarse spatial resolution hampers the radar backscattering. Synthetic aperture radar （SAR） with a high spatial resolution and all-weather observation abilities has become one of the most important tools for ocean wind retrieval, especially in the coastal area. Conventional methods of wind field retrieval from SAR, however, require wind direction as initial information, such as the wind direction from numerical weather prediction models （NWP）, which may not match the time of SAR image acquiring. Fortunately, the polarimetric observations of SAR enable independent wind retrieval from SAR images alone. In order to accurately measure coastal wind fields, this paper proposes a new method of using co-polarization backscattering coefficients from polarimetric SAR observations up to polarimetric correlation backscattering coefficients, which are acquired from the conjugate product of co-polarization backscatter and cross-polarization backscatter. Co-polarization backscattering coefficients and polarimetric correlation backscattering coefficients are obtained form Radarsat-2 single-look complex （SLC） data.The maximum likelihood estimation is used to gain the initial results followed by the coarse spatial filtering and fine spatial filtering. Wind direction accuracy of the final inversion results is 10.67 with a wind speed accuracy of 0.32 m/s. Unlike previous methods, the methods described in this article utilize the SAR data itself to obtain the wind vectors and do not need external wind directional information. High spatial resolution and high accuracy are the most important features of the method described herein since the use of full polarimetric observations contains more information about the space measured.This article is a useful addition to the work of independent SAR wind retrieval. The experimental results herein show that it is feasible to employ the co-polarimetric backscattering coefficients and the polarimetric correlation backscattering coefficients for coastal wind field retrieval.     

基于影像纹理特征和外部风向的星载 SAR 海面风场反演研究

在合成孔径雷达(Synthetic Aperture Radar,SAR)海面风场反演中,基于风条纹影像纹理特征的海面风向反演方法精度高,但是依赖于图像风条纹的存在,而外部风向信息与SAR资料时空分辨率不易匹配、精度较低,从而影响大面积、高分辨率海面风场反演的精度。针对此问题,提出一种将SAR图像风条纹线性纹理特征与外部风向信息相结合的星载SAR海面风向获取方法,在SAR影像线性纹理特征明显的区域采用二维连续小波变换得到高精度的海面风向,其余区域采用与之时空相匹配的数值预报模式风向填充;并利用地球物理模型函数进一步得到海面风速,进而实现高精度、大范围海面风场的反演。为验证本文方法的有效性,利用ENVISAT/ASAR数据进行风场反演试验,并将反演结果与浮标实测数据进行比对。结果表明:在线性纹理特征明显的区域,小波方法的反演精度优于快速傅里叶变换(FFT)法和数值预报模式风向;外部风向精度略低,但与SAR观测资料时空匹配性较好,弥补了风条纹风向的不足。二者的结合为星载SAR海面风场反演的业务化应用提供了支持。     

复合雷达后向散射模型与合成孔径雷达、散射计和高度计海面雷达后向散射观测的比较分析

海洋微波散射模型相比于以经验统计建立的地球物理模式函数具有不受特定微波频率限制的优势。组合布拉格散射模型和几何光学模型形成了复合雷达后向散射模型。利用南海北部气象浮标2014年海面风速风向实测值作为散射模型输入,分别比较了复合雷达后向散射模型与RADARSAT-2卫星C波段SAR、HY-2A卫星Ku波段微波散射计的海面后向散射系数,偏差分别为(?0.22±1.88) dB (SAR)、(0.33±2.71) dB (散射计VV极化）和(?1.35±2.88) dB (散射计HH极化);以美国浮标数据中心(NDBC)浮标2011年10月1日至2014年9月30日共3年的海面风速、风向实测值作为散射模型输入,分别比较了复合雷达后向散射模型与Jason-2、HY-2A卫星Ku波段高度计海面后向散射系数,偏差分别为(1.01±1.15) dB和(1.12±1.29) dB。中等入射角和垂直入射下的卫星传感器后向散射系数观测值与复合雷达后向散射模型模拟值比较,具有不同的偏差,但具有相同的海面风速检验精度,均方根误差小于1.71 m/s。结果表明,复合雷达后向散射模型可模拟计算星载SAR、散射计和高度计观测条件下的海面雷达后向散射系数,且与CMOD5、NSCAT-2、高度计业务化海面风速反演的地球物理模式函数的计算结果具有一致性;复合雷达后向散射模型可用于微波遥感器的定标与检验、海面雷达后向散射的模拟。     

台风中降雨对中国高分3号合成孔径雷达观测信号的影响

Gaofen-3(GF-3), a Chinese civil synthetic aperture radar(SAR) at C-band, has operated since August 2016.Remarkably, several typhoons have been captured by GF-3 around the China Seas over its last two-year mission.In this study, six images acquired in Global Observation(GLO) and Wide ScanSAR(WSC) modes at verticalvertical(VV) polarization channel are discussed. This work focuses on investigating the observation of rainfall using GF-3 SAR. These images were collocated with winds from the European Centre for Medium-Range Weather Forecasts(ECMWF), significant wave height simulated from the WAVEWATCH-III(WW3) model, sea surface currents from climate forecast system version 2(CFSv2) of the National Centers for Environmental Prediction(NCEP) and rain rate data from the Tropical Rainfall Measuring Mission(TRMM) satellite. Sea surface roughness,was compared with the normalized radar cross section(NRCS) from SAR observations, and indicated a 0.8 correlation(COR). We analyzed the dependences of the difference between model-simulated NRCS and SARmeasured NRCS on the TRMM rain rate and WW3-simulated significant wave height. It was found that the effects of rain on SAR damps the radar signal at incidence angles ranging from 15° to 30°, while it enhances the radar signal at incidence angles ranging from 30° to 45° and incidence angles smaller than 10°. This behavior is consistent with previous studies and an algorithm for rain rate retrieval is anticipated for GF-3 SAR.     

全极化SAR图像中溢油极化特征研究

相比于单极化SAR图像,全极化SAR图像不仅能体现海面目标的几何特征、后向散射特征,还能体现目标的极化特征。因此,在溢油检测方面,极化SAR更具优势。特征提取作为溢油检测的关键步骤,直接影响到溢油检测的精度。在本文中,我们分析了全极化SAR图像中海面溢油的极化特征,如极化散射熵、平均散射角等。并提出了新的极化特征P,该特征参数能够反映海面目标电磁散射过程中布拉格散射机制和镜面散射机制的比例。为了研究极化特征溢油检测的能力,本文基于SIR-C/X-SAR和Radarsat-2全极化SAR图像开展了相关实验,并对比分析了溢油的多种极化特征。实验结果显示,在中低风速情况下,C波段溢油探测效果优于L波段;本文提出的极化特征P对海面散射机制敏感;基准高度和特征参数P在C波段比其他极化特征更适于溢油检测。     

基于理论的气旋条件下双极化C波段合成孔径雷达波参数检测

Theoretical-based ocean wave retrieval algorithms are applied by inverting a synthetic aperture radar(SAR)intensity spectrum into a wave spectrum, that has been developed based on a SAR wave mapping mechanism. In our previous studies, it was shown that the wave retrieval algorithm, named the parameterized first-guess spectrum method(PFSM), works for C-band and X-band SAR at low to moderate sea states. In this work, we investigate the performance of the PFSM algorithm when it is applied for dual-polarization c-band sentinel-1(S-1) SAR acquired in extra wide-swath(EW) and interferometric wide-swath(IW) mode under cyclonic conditions.Strong winds are retrieved from six vertical-horizontal(VH) polarization S-1 SAR images using the c-band crosspolarization coupled-parameters ocean(C-3 PO) model and then wave parameters are obtained from the image at the vertical-vertical(VV) polarization channel. significant wave height(SWH) and mean wave period(MWP) are compared with simulations from the WAVEWATCH-III(WW3) model. The validation shows a 0.69 m root mean square error(RMSE) of SWH with a –0.01 m bias and a 0.62 s RMSE of MWP with a –0.17 s bias. Although the PFSM algorithm relies on a good quality SAR spectrum, this study confirms the applicability for wave retrieval from an S-1 SAR image. Moreover, it is found that the retrieved results have less accuracy on the right sector of cyclone eyes where swell directly affects strong wind-sea, while the PFSM algorithm works well on the left and rear sectors of cyclone eyes where the interaction of wind-sea and swell is relatively poor.     

A novel synthetic aperture radar scattering model for sea surface with breaking waves

In this study a novel synthetic aperture radar(SAR) scattering model for sea surface with breaking waves is proposed. Compared with existing models, the proposed model considers an empirical relationship between wind speed and wave breaking scattering to present the contribution of wave breaking. Moreover, the scattering weight factor p, and wave breaking rate q, are performed to present the contribution of the quasi-specular scattering term, Bragg scattering term, and wave breaking scattering t...     

海洋溢油合成孔径雷达图像特征提取及其关键度分析

就SAR图像溢油检测的方法论而言,用于识别溢油和疑似现象的定性或定量的统计特征量选择,通常是任意的。对于不同的分类模型,所选用的特征量也不尽相同。主要是进行海洋SAR图像特征提取及其关键度分析。其目的是将"最小距离"判别法应用于海上溢油和疑似溢油的识别研究。首先,针对海洋SAR图像溢油检测常用的特征量,进行冗余处理;然后,引入关键系数,定量地研究特征量的关键度,提取显著特征量;藉以构造一个多维的特征矢量空间,以适于最小距离判别法在特征矢量空间中进行溢油和疑似溢油的识别研究。     

Semisupervised heterogeneous ensemble for ship target discrimination in synthetic aperture radar images

Ship detection using synthetic aperture radar (SAR) plays an important role in marine applications. The existing methods are capable of quickly obtaining many candidate targets, but numerous non-ship objects may be wrongly detected in complex backgrounds. These non-ship false alarms can be excluded by training discriminators, and the desired accuracy is obtained with enough verified samples. However, the reliable verification of targets in large-scene SAR images still inevitably requires manual interpretation, which is difficult and time consuming. To address this issue, a semisupervised heterogeneous ensemble ship target discrimination method based on a tri-training scheme is proposed to take advantage of the plentiful candidate targets. Specifically, various features commonly used in SAR image target discrimination are extracted, and several acknowledged classification models and their classic variants are investigated. Multiple discriminators are constructed by dividing these features into different groups and pairing them with each model. Then, the performance of all the discriminators is tested, and better discriminators are selected for implementing the semisupervised training process. These strategies enhance the diversity and reliability of the discriminators, and their heterogeneous ensemble makes more correct judgments on candidate targets, which facilitates further positive training. Experimental results demonstrate that the proposed method outperforms traditional tri-training.     

背景场对变分方法海面风速反演结果的影响

利用前期提出的合成孔径雷达反演海面风场变分方法新解法,开展背景场对合成孔径雷达反演海面风场变分方法风速反演结果影响的模拟试验分析。模拟试验表明,变分方法有效解决了直接反演方法的两大缺陷:一是当背景场风速较大的时候,合成孔径雷达后向散射系数对风速不敏感,直接导致较大的风速反演误差;二是当背景场风向存在误差时,将导致后向散射系数更大的误差,进而导致风速反演结果更大的误差。进一步试验表明,当背景场风速较大时,变分方法风速误差低于直接反演方法风速误差。而当背景场风向误差较小时,直接反演方法风速误差比变分方法风速误差小。