PSI技术在地表形变监测中的应用研究

基于时序SAR影像准确识别PS是永久散射体合成孔径雷达干涉(PSI)技术建模及形变信息提取中最为关键的问题之一。本文提出了一种改进的PS探测算法,它是基于时序SAR影像的振幅信息,利用振幅和振幅离差指数双阈值法获取PS候选点,对所有候选点进行相位稳定性分析,筛选出既满足雷达反射强度高、又符合散射稳定性要求的真实PS点,并基于所选PS点提取形变信息。实验结果表明,相比于已有PS探测方法,本文所提出的方法能够更准确、可靠地识别出时序SAR影像中的PS目标,进而提高了PSI形变探测结果的精度和可靠性。     

基于ROC曲线的永久散射体识别最佳阈值定量筛选

永久散射体识别是用PS-InSAR方法获取地面沉降数据的关键环节之一,其最佳阈值的设定直接影响PS点的精度和密度。本文基于大数据统计的分析方法——ROC曲线法定量分析和确定PS点识别的最佳阈值。选择3种典型的PS识别方法,绘制每种方法在不同阈值条件下的ROC曲线图,当ROC曲线下面积越大,方法越优。依据最佳阈值位于ROC曲线左上部位的特征,采用敏感度与特异度之和（Se+Sp）最大的方法可定量判定出最佳阈值的取值。在最佳阈值条件下,识别的PS点具有正选率足够高、误选率足够小,PS点的密度足够大的特性。为进一步验证该方法的可行性,本文以北京龙潭公园地区为PS识别的实验区,用振幅离差指数法、相关系数法,以及两种阈值相结合的双阈值法3种方法进行实验识别PS点,并根据ROC曲线判得3种方法的最佳阈值。研究结果发现：（1）振幅离差T_D识别PS点的最佳阈值为0.45;相干系数Tγ识别PS点的最佳阈值为0.45;振幅离差T_D、相干系数Tγ双重阈值识别PS点的最佳阈值（T_D,Tγ）为（0.50,0.50）。（2）用振幅离差T_D和相干系数Tγ双阈值法识别PS点,得到的ROC曲线下面积AUC=0.762,高于单阈值法,表明双重阈值法识别PS点优于单一阈值的PS点识别方法。研究表明ROC曲线可定量化确定PS点的最佳阈值,而且该方法可进一步推广于GIS空间分析、遥感解译过程中阈值的定量化筛选。     

卫星重力梯度测量数据的粗差探测

分别讨论了阈值法、Dixon检验法和小波算法应用于卫星重力梯度数据粗差探测的效果。为了克服这3种单一粗差探测方法的不足,提出了卫星重力梯度数据的粗差探测组合方案,即联合Dixon检验和小波算法,以及联合Dixon检验、阈值法和小波算法的组合方案。模拟结果表明,两种组合方案均能有效改善粗差探测的效果。     

改进的PS探测方法及其应用

提出一种改进的永久散射体PS(Persistent Scatterer)探测方法,首先基于时序SAR影像的振幅信息,利用振幅和振幅离差指数双阈值法获取PS候选点,然后根据干涉相位空间相关性,对所有候选点进行相位稳定性分析,筛选出既满足雷达反射强度高、又符合散射稳定性要求的真实PS点,最后基于所选PS点提取形变信息。选取上海市局部区域作为实验区,以16幅TerraSAR-X(TSX)影像为数据源,进行PS探测和形变信息提取。结果表明,相比于已有的PS探测方法,本文方法能够更准确、可靠地识别出时序SAR影像中的PS点。形变结果显示,研究区域内最大沉降速率为-51mm/a,平均沉降速率为-15.8mm/a,以水准实测数据进行检核,验证了基于改进的PS探测方法进行地表形变信息提取结果的可靠性。     

PSInSAR永久散射体的自动探测

为了有效探测合成孔径雷达差分干涉测量中的永久散射体,综合考虑永久散射体对雷达波的强反射特性和散射的稳定性,本文提出了三重阈值自动探测算法,即时序相关系数、振幅离差和振幅指数三重阈值串行结合的算法.该方法首先考虑回波信号的高信噪比特性,用平均相干系数和振幅两道阈值挑选出永久散射体候选点,然后考虑永久散射体强稳定性,用振幅...     

一种改进的CFAR船只探测方法

提出了一种改进的CFAR船只探测算法。该方法采用PNN模型来估计海面雷达后向散射的概率分布模型,利用CFAR技术来确定整体阈值,采用基于交叉验证技术的黄金分割搜索法估算高斯分布的形状参数,使用区域生长法去除虚警。使用Radarsat图像对该方法进行了检验,并与改进前的算法进行了比较,结果显示该文的探测算法在探测精度和探测速度上均明显优于改进前的算法。     

激光扫描点云准确快速去噪方法

激光点云数据中孤点和离群点等噪声的自动去除方法是激光点云数据处理的研究热点。本文针对现有孤点的平均点间距阈值探测法存在远距离点云误判的问题,对平均点间距附加距离权重后再根据阈值进行了判断;针对离群点的生长探测法存在效率低的问题,采用均匀八叉树结构以格网为单位进行了生长探测。试验证明了改进方法的自适应性和高效性。     

基于SBAS-InSAR技术的大坝形变探测与监测

针对大坝安全运营的形变监测问题,研究基于多基线干涉合成孔径雷达（SBAS-InSAR）技术的大坝形变探测与监测方法。设置时间基线阈值,生成大坝差分干涉相位图;利用改进的戈尔茨坦滤波（Goldstein）算法,滤波处理大坝差分干涉相位图;采用最小不连续的区域增长解缠算法,相位解缠大坝差分干涉相位图;通过相干系数阈值法,在大坝相位解缠图内选取高相干点;建立大坝形变探测与监测的高程测量估计数学模型;通过奇异值分解法,求解数学模型,实现大坝探测与监测结果。实验证明：该方法可有效生成大坝差分干涉图,并去除大坝差分干涉图的内部噪声;可有效探测与监测大坝内各监测点的形变量。     

自适应阈值定权最小二乘3D匹配算法

针对点云精配准中最小二乘3D算法的先验权值无法自动确定的问题,提出了一种自适应阈值定权的最小二乘3D匹配算法。以待匹配点云与目标点云中对应同名点间欧式距离作为约束条件,通过自适应阈值的方式,对同名点先验权重系数进行约束,提高了先验权重系数的有效性。通过实验证明,自适应阈值约束算法提高了最小二乘3D算法的精度和收敛速度,且优于主流的迭代最邻近点算法。     

PSInSAR中PS的自动探测

为了有效探测PSInSAR中的永久散射体,充分考虑永久散射体对雷达波的强反射特性及强稳定性,文中提出三阈值探测法,即联合采用时序相关系数、振幅离差和振幅指数3重阈值串行结合的算法,该方法首先考虑雷达回波信号的强信噪比,用平均相干系数和振幅两道阈值挑选出永久散射体候选点,然后考虑永久散射体强稳定性,用振幅离差阈值从永久散射体后选点中进一步精选出永久散射体。最后利用澳门地区的30幅Envisat影像进行实验,证明该方法有效且可靠。     

PS-InSAR技术地面沉降研究与展望

近年来,合成孔径雷达差分干涉测量(D-InSAR)技术在许多领域取得了良好的应用成果,但D-In-SAR确受时间失相干因素影响很大,同时大气效应也会影响D-InSAR的测量精度。1999年Ferrettit提出了永久散射体技术(Perm anent Scatterer,PS),它通过识别SAR图像中的永久散射体,消除大气影响,充分利用长基线距的干涉图像对,最大限度地提高数据的利用率,能取得毫米级的地表形变测量精度,因而大大增强了干涉测量的环境适应能力及其精度。本文着重介绍了PS技术原理,对其与D-InSAR相互关系进行了讨论,最后在地面沉降监测等领域开展这项研究潜力进行了展望。     

基于雷达干涉永久散射体网络探测地表形变的算法与实验结果

为削弱常规卫星DInSAR技术在区域地表形变探测应用中时空失相关与大气延迟的负面影响,探索和发展了基于永久散射体(PS)观测网络建模与参数稳健估计的算法并开发一套完整的计算程序,可达到分离和提取线性与非线性形变时间序列、地形数据误差与大气信号的目的。以上海市沉降场为对象,选取1992~2002年间ERS-1/2卫星所获取的26幅SAR影像为源数据,分别开展模拟和真实数据的实验,证实该算法和计算程序是有效而可靠的。     

Assessment of number and distribution of persistent scatterers prior to radar acquisition using open access land cover and topographical data

Persistent scatterer synthetic aperture radar interferometry (PSI) is a powerful remote sensing technique to detect and measure deformation of the Earth‘s crust – such as subsidence and landslides – with an accuracy of a few millimeters. Deformation is measured at specific points in a radar image called persistent scatterers (PS), which are characterized by long-term constant backscattering properties (high coherence) of the radar signal. Reliable PSI processing requires a stack of 15–50 SAR images and more, and processing is time-consuming (computational costs) and expensive (referring to both, costs for the SAR data and labor costs). Previous research for PS assessment used already acquired SAR data. This paper presents two new methods for predicting PS prior to the radar recording of the area of interest using freely available or low-cost land cover data, topographical maps and OpenStreetMap data. In the procedure, the distance between the assessed PS is calculated and classified regarding to the applicability for PSI processing. Additionally, the dispersion of the assessed PS within the site is analyzed. The results of the two assessment methods are validated using data of real PSI processing. Here, we show that the developed PS assessment techniques are fast and reliable tools to test the spatial applicability of PSI.     

Comparison of ERS-SAR and spot data for sugar beet crop cover assessment

The present work was aimed to compare the abilities of radar and optical satellite data to estimate crop canopy cover, which is a key component of productivity estimates. Three ERS-1 SAR images were obtained of East Anglia (UK) in 1995 and one ERS-2 SAR image in 1996. The images covered a study area around the IACR Brooms Barn Sugar Beet Research Institute. Field data comprising radiometric and biophysical measurements of the crop canopy were collected in two fields from June 22 to August 3, 1995 to coincide with ERS-1 SAR overpass dates. In 1996, field data were collected in two fields from June 11 to July 29 on a weekly basis. A previously calibrated version of the water cloud model was inverted to estimate Leaf Area Index (LAI) from ERS-1 and ERS-2 SAR backscatter and soil moisture samples. Canopy cover was estimated from the radar-estimated LAI using a standard exponential relationship that has a well-established coefficient for sugar beet. Radio-metrically and atmospherically corrected data from three SPOT images in 1995 and one SPOT image in 1996 were used to calculate the Optimised Soil Adjusted Vegetation Index (OSAVI), from which crop canopy cover was estimated using a relationship determined previously by canopy modelling. The crop cover values estimated by satellite were in good agreement with those measured on ground with the Parkinson radiometer. Radar data may be able to provide useful estimates of canopy cover for crop production modelling, especially in the case of loss of optical data due to cloud.     

An efficient application of fusion approach for hot spot detection with MODIS and PALSAR-1 data

Hot spot detection with satellite images, especially with synthetic aperture radar (SAR) images is still a challenging task. Several researchers have used TM/optical data for identification of hot spot but the use of SAR data is very limited for this type of application. The fusion of SAR data with TM/optical data may add additional information which in turn will lead for enhancement of detection capability of the hot spot. Therefore, this study explores the possibility of fusion of Moderate Resolution Imaging Spectroradiometer (MODIS) and Phased Array L-band Synthetic Aperture Radar (PALSAR) satellite images for the hot spot detection. Image fusion is emerging as a powerful tool where information of various sensors can be used for obtaining better results. For this purpose, vegetation greenness and roughness information which is obtained from MODIS and PALSAR satellite images, respectively, are used for fusion, and then, a contextual-based thresholding algorithm is applied to the fused image for hot spot detection. The proposed approach comprises of two steps: (1) application of genetic algorithm-based scheme for image fusion of MODIS and PALSAR satellite images, and (2) classification of the fused image as either hot spot or non-hot spot pixels by employing a contextual thresholding technique. The algorithm is tested over the Jharia Coal Field region of India, where hot spot is one of the major problems and it is observed that the proposed thresholding technique classifies the each pixel of the fused image into two categories: hot spot and non-hot spot and the proposed approach detects the hot spot with better accuracy and less false alarm.     

永久散射体差分干涉测量技术中SAR影像精配准的一种新方法

提出并实现了一种基于加权最小二乘的低相干SAR像对精配准新方法。该方法借助一幅与主、辅影像相干性都较高的第三幅影像来完成低相干SAR影像对的初步配准,利用加权最小二乘法求出二者间的坐标映射函数,从而快速高效地实现低相干SAR影像对的高精度亚像元级配准。采用ERS-1/2实际数据的配准实验,验证了该方法可以提高低相干SAR像对的干涉图质量,提高二者之间的相干性和控制点的配准精度,改善低相干SAR影像对的配准效果,在一定程度上解决了PS InSAR技术中低相干SAR影像对的配准问题。     

Exploring The Generation Of Digital Elevation Models From Same-Side Ers Sar Images: Topographic And Temporal Effects

This paper presents an attempt to explore the generation of digital elevation models (DEMs) by radargrammetry from same-side ERS-1/2 synthetic aperture radar (SAR) images. Two ERS-1 and two ERS-2 C-band (wavelength 5·6 cm) SAR images along parallel descending orbits, acquired in 1996 and 1997, are used to form four stereopairs. The test area is western Hong Kong which is dominated by mountains/hills that are largely covered by evergreen-broadleaf trees. The stereopairs covering the same area but with different time intervals (varying from 16 days to 1·5 years) have an intersection angle of 4·5° and a relatively small overlap of 30% (30 km). In addition to the effect of topography, the effect of temporal correlation on the accuracy of the resulting DEMs is also analysed for the first time. From the experimental results obtained in this study, the following conclusions may be drawn: (a) with same-side ERS-1/2 SAR images, an accuracy of 30 to 35 m is achievable; (b) the accuracy of a resulting DEM degrades almost linearly with an increase in slope when the terrain slope is below 30°, and in the areas with slope over 30°, the accuracy of the DEM is significantly degraded and even becomes unacceptable; (c) the worst accuracy is obtained in the foreslope directions and the best accuracy is obtained in the backslope directions; (d) the time interval between two SAR images has no significant effect on the accuracy of the DEM in general; (e) the time interval between two SAR images has no significant effect on the reliability of image matching.     

ENVISAT ASAR重轨INSAR用于东南极冰盖格罗夫山角峰地区冰流探测的初步结果

由于可以探测到视线向的微小形变量，重复轨道雷达干涉测量（INSAR）成为探测极地冰流的有效手段。基于ERS-1／2SAR影像的INSAR已经成功获取了南北极许多地区的冰流信息。采用最新的ENVISAT ASAR影像，利用干涉方法获得了东南极内陆格罗夫山地区的首幅ASAR干涉条纹图（其中包括地形信息和冰流信息）。其与利用该地区1996年ERS-1和JERS-1数据所获得的干涉条纹进行对比表明，在格罗夫山角峰群内分布有两个冰流子系统，且状态较为稳定，ENVISAT ASAR数据在冰盖干涉测量方面具有良好的性能和应用潜力。     

航天雷达遥感的作用与发展

本文论述了迄今为止唯一获得地球表面航天雷达图像的Seasat SAR、SIR-A及SIR-B三颗成象雷达系统在地球科学研究中的作用,对未来十年以ALMAZ ZAR、ERS-1 SAR、JERS-1 SAR、SIR-C、Radarsat SAR和EOS SAR为主的国际性主动微波遥感系统进行分析,指出研究过程中新的概念和趋势,展望了90年代航天雷达遥感技术发展及应用的前景.     

粗／精轨道数据对卫星InSAR DEM精度影响的对比分析

本文在介绍InSAR系统中卫星轨道状态矢量内插方法的基础上，从理论和实际两方面分析了轨道数据误差对参考椭球面相位、地形干涉相位和数字高程模型（DEM）精度的影响。以上海局部地区作为实验场，采用ERS-1／2卫星SAR影像数据，分别使用欧洲空间局粗略轨道数据和荷兰Delft大学空间研究中心精密轨道数据进行了干涉处理，生成了两种情况下的DEM，并对相关精度进行了对比与分析。研究结果表明，使用精轨数据建立的DEM的精度明显高于基于粗轨数据建立的DEM的精度。