基于同步风场的机载SAR海浪参数反演方法

针对机载合成孔径雷达(SAR)对海探测特点,采用多入射角法从SAR数据本身得到与海浪参数反演区域时空匹配的同步海面风速和风向,并结合线性变换关系,计算得到海浪初猜谱对应的仿真SAR图像谱,将仿真SAR图像谱和观测SAR图像谱输入代价函数中进行迭代运算,通过非线性方程的解算得到最适海浪谱;采用交叉谱法去除海浪传播180°方向模糊,最终得到海浪参数。论文提出的基于同步风场的机载SAR海浪参数反演方法,充分利用了机载SAR海洋环境探测的优势,解决了传统SAR海浪参数反演中初猜谱构造依赖外部风场的问题,机载同步飞行试验的海浪参数反演结果与浮标观测值的有效波高、波向的均方根误差分别为0.23 m和13.23°,验证了该方法的有效性,可为机载SAR海浪参数反演业务化提供支持。     

Measurement of ocean surface winds using synthetic aperture radars

A methodology for retrieving high-resolution ocean surface wind fields from satellite-borne synthetic aperture radar (SAR) data is introduced and validated. The algorithms developed are suited for ocean SAR data, which were acquired at the C band of either vertical (VV) or horizontal (HH) polarization in transmission and reception. Wind directions are extracted from wind-induced streaks that are visible in SAR images of the ocean at horizontal scales greater than 200 m. These wind streaks are very well aligned with the mean surface wind direction. To extract the orientation of these streaks, two algorithms are introduced, which are applied either in the spatial or spectral domain. Ocean surface wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated SAR images, together with the local SAR-retrieved wind direction. Therefore, several C-band models (CMOD IFR2, CMOD4, and CMODS) are available, which were developed for VV polarization, and have to be extended for HH polarization. To compare the different algorithms and C-band models as well as demonstrate their applicability, SAR-retrieved wind fields are compared to numerical-model results considering advanced SAR (ASAR) data from Environmental Satellite (ENVISAT), a European satellite.     

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。     

高海况海洋遥感信息提取技术研究进展

中等海况下,星载合成孔径雷达(Synthetic Aperture Radar,SAR)已经广泛应用于海洋动力环境要素的监测(风场、波浪、流场)。近年来,SAR高海况遥感,尤其是探测台风海面风场、巨浪、流场已经成为国内外研究热点,并突破了一些关键技术。利用SAR多极化成像模式对海观测和新发展的地球物理模式函数,可以提取高海况下的海面风速、风向、有效波高、流速和流向等海洋表面关键物理参数。这些环境要素可以用于海洋灾害监测预警;为海洋和大气数值模式提供准确的初始场和同化源,改进模式预报精度;为研究全球气候变化提供有力的观测依据。     

A semiempirical algorithm for SAR wave height retrieval and its validation using Envisat ASAR wave mode data

Many synthetic aperture radar(SAR) wave height retrieval algorithms have been developed.However,the wave height retrievals from most existing methods either depend on other input as the first guess or are restricted to the long wave regime.A semiempirical algorithm is presented,which has the objective to estimate the wave height from SAR imagery without any prior knowledge.The proposed novel algorithm was developed based on the theoretical SAR ocean wave imaging mechanism and the empirical relation between two types of wave period.The dependency of the proposed model on radar incident and wave direction was analyzed.For Envisat advanced synthetic aperture radar(ASAR) wave mode data,the model can be reduced to the simple form with two input parameters,i.e.,the cutoff wavelength and peak wavelength of ocean wave,which can be retrieved from SAR imagery without any prior knowledge of wind or wave.Using Envisat ASAR wave mode data and the collocated buoy measurements from NDBC,the semiempirical algorithm is validated and compared with the Envisat ASAR level 2 products.The root-mean-square-error(RMSE) and scatter index(SI) in respect to the in situ measurements are 0.52 m and 19% respectively.Validation results indicate that,for Envisat ASAR wave mode data,the proposed method works well.     

基于SAR极化比和纹理特征的海面溢油识别方法

针对海洋表面SAR影像的特点，采用基于灰度共生矩阵的纹理特征方法是提取海面溢油信息的常用方法，但实际海洋表面复杂的信息使得SAR图像上产生类似溢油现象的暗斑区域，这导致在利用纹理特征方法提取溢油信息时存在虚警率，降低了溢油信息的提取精度。基于RADARSAT-2 SAR四极化影像，本文提出基于SAR极化比影像的纹理特征识别方法对海面油膜进行识别提取。结果显示，基于SAR极化比影像的纹理特征识别方法可以有效且准确地提取海面溢油信息，相比于VV极化影像的纹理特征识别方法，溢油监测过程中的虚警率降低了17.96%，溢油监测总体精度达到96.83%。     

利用浅水地形及其SAR影像确定海面风向的一种方法

利用浅水地形的SAR影像以及基于浅水地形SAR仿真模型计算得到的仿真SAR影像,基于仿真SAR影像与真实SAR影像之间的相关性提出了一种确定海面风向的方法——最大相关系数法.以南沙双子礁海域为例,利用最大相关系数法确定出了一幅RADARSAT SAR影像成像时刻的海面风向,通过对结果的比较分析可以看出对于包含浅水地形的SAR影像应用该方法探测海面风向是可行的.     

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.     

海上溢油极化特征及其探测研究

The SAR(Synthetic Aperture Radar) has the capabilities for all-weather day and night use. In the case of determining the effects of oil spill dumping, the oil spills areas are shown as dark spots in the SAR images.Therefore, using SAR data to detect oil spills is becoming progressively popular in operational monitoring, which is useful for oceanic environmental protection and hazard reduction. Research has been conducted on the polarization decomposition and scattering characteristics of oil spills from a scattering matrix using allpolarization of the SAR data, calculation of the polarization parameters, and utilization of the CPD(Co-polarized Phase Difference) of the oil and the sea, in order to extract the oil spill information. This method proves to be effective by combining polarization parameters with the characteristics of oil spill. The results show that when using Bragg, the oil spill backscattering machine with Enopy and a mean scatter α parameter. The oil spill can be successfully identified. However, the parameter mechanism of the oil spill remains unclear. The use of CPD can easily extract oil spill information from the ocean, and the polarization research provides a base for oil spill remote sensing detection.     

Nearshore Wave Field Analysis Using SAR Images

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GF-3号SAR卫星遥感围填海监测方法研究——以大连金州湾为例

依据不同围填海类型在高分三号(GF-3)合成孔径雷达(synthetic aperture radar,SAR)卫星遥感影像上可分性,建立围填海遥感分类体系及相应的围填海类型解译标志,进而分析SAR图像岸线提取方法,构建GF-3围填海监测技术流程。采用几何主动轮廓模型进行GF-3 SAR影像自动提取海岸线,获得围填海专题图。通过外业精度调查验证GF-3 SAR卫星遥感影像可以有效获取围填海信息。     

基于C-2PO模型和CMOD5.N地球物理模式函数的SAR风速反演性能评估

本文选取142幅RADARSAT-2全极化合成孔径雷达（SAR）影像，在没有入射角输入的情况下，首先利用C-2PO模型进行海面风速反演。随后，将同一时空下的ASCAT散射计风向作为初始风向，提取相应雷达入射角，利用地球物理模式函数（GMF） CMOD5.N对142幅SAR影像进行风速计算。反演结果与美国国家资料浮标中心海洋浮标风速数据对比，结果显示:CMOD5.N GMF和C-2PO模型均可反演出较高精确度的海面风速，其均方根误差分别为1.68 m/s和1.74 m/s。此外，研究发现，在低风速段，CMOD5.N GMF的风速反演精度要明显优于C-2PO模型。针对这一现象，本文以SAR系统成像机理为基础，以低风速SAR图像为具体案例，给出了3种造成这一现象的原因。     

Ocean wave parameters retrieved directly from compact polarimetric SAR data

We aim to directly invert wave parameters by using the data of a compact polarimetric synthetic aperture radar(CP SAR) and validate the effectiveness of ocean wave parameter retrieval from the circular transmit/linear receive mode and π/4 compact polarimetric mode. Relevant data from the RADARSAT-2 fully polarimetric SAR on the C-band were used to obtain the compact polarimetric SAR images, and a polarimetric SAR wave retrieval algorithm was used to verify the sea surface wave measurements. Usin...     

对ENVISAT ASAR level2算法固有误差的分析

欧洲空间局的ENVISAT ASAR level 2算法是从合成孔径雷达(SAR)单视复图像反演涌浪方向谱的算法.该算法假设双峰海浪谱的SAR图像交叉谱是涌浪的图像交叉谱和风浪的图像交叉谱之和.实际上双峰海浪谱的SAR图像交叉谱中还有一个混合项,正是该混合项导致ENVI-SAT ASAR level 2算法有固有误差.利用遥感仿真的方法分析了不同海况条件下该算法的这一固有误差,结果表明,只有在有效波高较小、或风浪的成分较少、或双峰海浪的传播方向较靠近SAR距离向、或波长较长时固有误差才较小,ENVISAT ASAR level 2算法对海浪谱的反演才较为适用.     

合成孔径雷达图像中海洋内波的特征检测

海洋内波在合成孔径雷达(SAR)图像中具有特定纹理分布,因此可以根据海洋内波SAR图像的纹理分布特性,进行内波海面特征检测。利用功率谱对具有不同纹理特征的SAR图像进行分析,并对特征进行分类统计得出内波的功率谱特征。在海洋内波区域,利用多孔小波变换及多尺度融合提取海洋内波特征,在此基础上对波-流散射系数进行提取。提出了"内波特征的功率谱特征-多孔小波综合检测算法",为海洋内波参数反演奠定了基础。     

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。     

Separation of ocean features from multifrequency full-polarization SAR imagery

Different ocean features usually appear in synthetic aperture radar (SAR) images simultaneously. This makes the image compli- cated and hard to understand. Because of lower signal-to-noise rate , it is much more difficult to separate different ocean features than to separate different land features. A completely novel method is presented to separate ocean features from multifrequency po- larimetric SAR imagery. AIRSAR data from Jet Propulsion Laboratory (JPL), National Aeronautics and Space Administration (NASA) are used in the case studies and good results are achieved.     

基于合成孔径雷达影像的海洋溢油纹理特征参数分析

溢油已是当前海洋生态环境破坏的主要因素之一,因此对海洋溢油的检测分析是当前海洋环境保护的一个重要课题。传统的溢油提取仅仅是单独依靠光学影像的光谱信息或者合成孔径雷达(SAR)影像的后向散射系数信息进行提取,这会造成很多同谱异物或者粗糙度相近似的地物错分,因此除了利用传统的影像信息以外,还需结合影像的纹理信息,从而提高溢油提取的精度,减少错分地物的数量。选用2006年渤海地区的三景同轨SAR影像作为数据基础,应用基于灰度共生矩阵的方法对其进行纹理分析。该方法可以很好地对图像区域和表面进行感知并能够从像元的灰度相关性上对纹理特征进行详细描述,因此适合于SAR影像的海洋溢油检测。在纹理分析的过程中有很多的参数需要选择,参数选择的好坏将直接影响最终提取结果的精度。通过对纹理分析过程中的参数进行讨论、实验、选择与验证,最终确定了基于灰度共生矩阵纹理分析中各参数的值,并选择了局部平稳、非相似性、对比度、变化量4个特征量作为溢油提取的纹理特征统计量。将纹理特征与SAR自身的后向散射系数相结合,通过神经网络分类法对其进行分类,并计算出分类精度为80.65%,分类效果良好。由此说明了将影像的传统信息与纹理信息相结合进行溢油提取是一种可行而有效的方法,同时也为后续的海洋溢油检测工作奠定了一定的基础。     

Modification of SAR spectra associated with surface wind fields in the sea off the Kii Peninsula: A case study

Using surface wave parameters and a high-resolution surface wind field derived from Synthetic Aperture Radar (SAR) image mode data, we have investigated the spatial modification of SAR spectra. We found a surface wind front, formed by sheltering effect of the Kii Mountains, separating high and low wind-speed regions in a sea area of an European Remote-Sensing Satellite (ERS) SAR image off the Kii Peninsula. A swell system propagating westward dominates in the whole sea area covered by the SAR image. The wavelength retrieved from the SAR spectra in the sheltered (non-sheltered) region is longer (shorter). Since the distributions of surface wave parameters and surface wind speed are so well correlated, it can be considered that the SAR spectra are modified differently by the sheltered/non-sheltered surface winds. In order to examine the phenomena observed on the SAR image we have estimated the wind-wave SAR spectrum using the SAR surface winds, a wind-wave spectrum model and a SAR wave imaging model. We assume that the SAR spectrum related to the swell is homogeneous in the area imaged by SAR, and that the SAR spectrum of the wind-wave components causes the observed SAR spectra modification. Differences between the observed SAR spectra and the estimated SAR spectra in the sheltered and non-sheltered regions agree well with each other. In the present case, it can be concluded that the observed SAR spectra can be regarded as a linear combination of the wind-wave SAR spectra and the swell SAR spectra.     

Estimates of ocean wavelength and direction from X-and L-band synthetic aperture radar data collected during the Marineland experiment

Simultaneously obtainedX- andL-band synthetic aperture radar (SAR) data collected during the Marineland Experiment were spectrally analyzed by fast Fourier transform (FFT) techniques to estimate ocean wavelength and direction. An eight-sided flight pattern was flown over the same ocean area in order to study the sensitivity of the spectral estimate on radar look direction. These spectral estimates were compared with in situ wave measurements made by a pitch-and-roll buoy. The comparison revealed that theX-band SAR detected all gravity waves independent of radar look direction, while theL-band SAR detected all range-traveling gravity waves but failed to detect waves in three of four cases in which the waves were traveling within 25° of the azimuth direction. The analysis also indicates that azimuth-traveling waves appear longer and more range-traveling in the SAR imagery than observed by in situ instrumentation. It is postulated that degraded azimuth resolution due to scatterer motion is responsible for these observations.