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。     

短基线INSAR相干点探测及应用

提出一种结合子孔径相关测度的时序高相干点探测方法,首先对时序SAR影像进行谱分解获得子孔径视图,通过时序子孔径相关测度进行强散射点筛选,然后分别根据振幅离差和干涉相位空间相关性,对目标点进行相位稳定性分析,探测出既满足强散射且在时间序列上散射稳定的高相干点。利用改进的点探测方法和短基线INSAR技术,对北京2003—2009年间40景ASAR影像进行相位建模,获取地面沉降时空分布特征,分析典型地物时序沉降过程,研究北京地面沉降与地下水开采关系。结果表明:相比已有方法,本文结合子孔径相关测度的高相干点探测结果更准确可靠;利用本文点探测方法反演的历史累积沉降信息,与水准结果一致,平均速率之差在3.69 mm/a以内,中误差为1.36 mm/a;研究区地面沉降最大速率达92.25 mm/a,空间不均匀分布明显,地面沉降量与地下水开采量呈分段的非线性相关。     

高分辨率PSI上海市沉降探测及分析

本文在改进的永久散射体(PS)探测方法基础上,应用高分辨率永久散射体雷达干涉(PSI)探测上海市地表沉降,并对沉降原因进行了详细分析。实验选取2008年4月至2010年1月间,由德国卫星TerraSAR-X(TSX)所获取的18幅X波段(波长为3.1 cm)高分辨率SAR影像为数据源,进行PS探测、PSI建模、形变提取和分析。实验结果表明,改进的PS探测方法探测出的PS点是合理和可靠的,且高分辨率SAR影像对地面硬目标识别能力较强,显著提高了PS点的密度和覆盖范围。沉降探测结果显示,最大相对沉降速率达30 mm/yr,平均沉降速率为11.5 mm/yr。     

基于永久散射体雷达差分干涉测量的城市地面沉降研究——以上海地面沉降监测为例

基于永久散射体雷达差分干涉测量技术,提出探测水久敞射体的振幅信息双阈值方法,研究上海陆家嘴地区在1992～2002年的地面沉降,获得该地区的线性和非线性沉降量以及区域沉降场,证实了地表形变在1 km范围内具有强相关性.结果显示陆家嘴地区在1992～2002年间的线性沉降速率为13.2 mn/a,总体半均沉降速率为16.8 mm/a,与实测结果之间具有较高的一致性.研究表明,PS-DInSAR技术不仪可有效探测地表离散目标的线性形变,还可探测其非线性形变以及获取地表区域形变场,并且可监测地表形变的时序变化过程.除了可用于城市沉降监测外,PS-DInSAR技术还可用于地震、火山、滑坡等地质灾害的监测.     

PSI技术在上海地表沉降监测中的应用

应用永久散射体雷达干涉(PSI)技术进行地表沉降监测研究,对PSI建模时采用的各相位分量的空间相关特性和沉降结果精度进行详细分析。试验选取覆盖上海地区的16幅高分辨率TerraSAR-X(TSX)SAR影像为数据源,进行PSI建模、形变提取和精度分析,并使用地面水准数据进行对比验证。结果表明,根据PS各相位分量的空间相关特性进行PS点的识别是合理的。与水准数据对比,两类年沉降速率结果具有很好的一致性,差异均值和标准偏差分别为1.6 mm/a和±4.6 mm/a,最小和最大差异量分别为0.198 7 mm/a和10.132 mm/a,证实了PSI技术在上海地区地表沉降监测的应用是有效和可靠的。     

利用时序DInSAR监测填海造陆地区地表沉降

通过研究时序DInSAR相位模型,利用振幅离差、时间相干系数和统计分析多重方法提取了相干点目标,并根据不同相位分量的时空特性分离出形变相位,继而提取出相干点目标上的沉降速率。以上海市临港新城主城区为实验区,利用24景Envisat ASAR影像,得到了2007-10～2010-02间的沉降速率分布,并分析了冲填土年代对沉降的影响。     

PS-InSAR在沛县矿区地表沉降监测中的应用

以徐州北部重要煤矿产地沛县为例,采用永久散射体时序分析技术(PS-In SAR)对2007~2011年间的18景ALOS PALSAR影像进行时序分析,反演了该地区这4 a间由于煤矿开采造成的地表形变过程。实验结果表明,(1)实验区域存在两处较大矿区形变,分别为沛城煤矿和孔庄煤矿,其沉降中心区沉降速率分别达到-38 mm/y和-18 mm/y,且与实际矿区的空间分布位置一致;(2)受孔庄煤矿开采的影响,沛县北部的省道321以及县内道路沉降也较为明显,沉降速率为-8 mm/y;(3)其他形变区域中心形变速率为-6^-16 mm/y。     

基于时序合并的PS-InSAR方法在雄县及周边区域地表形变监测中的应用

本文提出了一种基于时序合并的PS-InSAR(TSC-PS-InSAR)监测方法,提取雄县及周边区域地表形变信息。形变区域最大沉降速率为-79 mm/a,沉降原因为地下水超采。结果表明,TSC-PS-InSAR方法在无需先验模型的条件下,能显著提高PS目标数量,且监测结果与StaMPS方法提取的形变信息在沉降趋势及沉降量级上保持了良好的一致性,验证了本文方法在实际应用中的可靠性和可行性。     

黄土填方区地表沉降时序InSAR监测分析

“削山填沟造地”等岩土工程在湿陷性黄土沟壑地区屡见不鲜,掌握填方区沉降情况具有重要意义。本文收集了2017年11月—2020年12月获取的56景TerraSAR-X StripMap模式影像,利用时序InSAR技术监测了陕北某湿陷性黄土填方地基工程的沉降信息,并与2017年11月—2020年12月期间监测区3个水准点的沉降测量结果比对。结果表明,在填方区地表以沉降为主,在挖方区地表以抬升为主,研究区存在有1处较为明显的地表沉降情况,位于填挖边界线附近填方区内,形变速率范围为-40~-20 mm/a,最大形变速率达-49.9 mm/a,累计量为-151.6 mm,时序InSAR形变结果和实地水准结果吻合性较好,垂直方向形变速率中误差为1.8 mm/a,表明时序InSAR技术在湿陷性黄土填挖方区变形监测中具有较好的应用价值。     

复杂环境下地基SAR粗差探测及应用

雷达视线受施工机械等的间断遮挡导致部分影像产生相位奇异值，从而造成解缠错误及误差传递，简单的相关影像处理难以识别受遮挡影像。本文提出了改进的基于小波变换的信号奇异性检测方法，通过对地基SAR PS点时序相位特征进行分析，将遮挡影像识别转化为粗差探测问题；由PS点相位序列与影像位置关系，根据测区PS点相位序列的奇异点集合得到受遮挡影像集；最后将受遮挡影像剔除后得到的地基SAR监测结果与精密全站仪、水准与游标卡尺数据进行对比分析。结果表明：本文提出的方法用于受遮挡影像的识别是可行的，解决了地基SAR在实际工程应用中可能存在的影像遮挡带来的测量数据含有粗差的问题，提高了监测区域伪影像检测的效率与准确性。     

PALSAR和ASARPSI显著地表沉降探测与分析

永久散射体雷达干涉(PSI)已被广泛应用于城市缓慢沉降监测,但针对显著性地表沉降监测及PSI适用性的探讨较少。本文选取天津市与廊坊市城郊结合部的典型工业化城镇为研究区,分别以2007至2010年间的23幅L波段(23.6 cm)ALOS PALSAR影像和2007至2009年间的23幅C波段(5.6 cm)ENVISAT ASAR影像为数据源,使用基于相位空间相关性分析的PSI方法进行时空沉降提取,并对两个平台的结果进行对比分析和交叉验证。在此基础上,结合长短波SAR对沉降敏感性不同的特征探讨该PSI方法应用于显著沉降解算的可靠性,并结合地质条件及地下水开采信息对实验区沉降的时空分布进行深入分析和解释。研究表明,两平台的沉降结果十分吻合,在沉降漏斗区二者均方根误差(RMSE)为6.5 mm/a;实验区地表沉降呈现出显著的非均匀性,最大沉降速率超过200 mm/a,造成严重沉降的主要原因为地下水的大量开采;证实了PSI方法在显著地表沉降监测方面的有效性和可靠性。     

An iterative PS-InSAR method for the analysis of large spatio-temporal baseline data stacks for land subsidence estimation

South-west of Tehran, the capital city of Iran, is subjected to a high deformation rate due to excessive groundwater extractions. Persistent Scatterrer SAR Interferometry (PS-InSAR) technique is used to monitor Tehran’s deformation. Three time series data including two Sentinel-1A (S-1A) spanning from 2014 to 2017, and an ENVISAT-ASAR data stack spanning from 2004 to 2010, are analyzed. The PS-InSAR technique does not perform well on ENVISAT-ASAR due to poor selection of PS points induced by large perpendicular baselines and strong temporal decorrelation of the dataset. In this paper, a novel Iterative PSI method (IPSI) is proposed to increase the PS points which are lost in PS-InSAR technique because of the unsuccessful derivation of the absolute phase value due to an integer ambiguity. The method selects PS points based on simultaneous analysis of their amplitude and phase. Results demonstrate that the density of PSs has been increased by about 4.5 times. Line of Sight (LOS) velocities obtained from both S-1A and ENVISAT-ASAR data analysis are highly compatible with each other, indicating the reliability of the both applied methods. The maximum cumulative displacements are estimated as 39.6 cm and 88.4 cm for Sentinel-1A and ENVISAT-ASAR datasets respectively. Moreover, the subsidence area has grown in the period between the data acquisition time. The methods are successfully validated by subsidence rates obtained from precise leveling and GPS observations.     

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.     

Subsidence monitoring in coal area using time-series InSAR combining persistent scatterers and distributed scatterers

In coal mining areas, ground subsidence persistently happens, which produces serious environmental issues and affects the development of cities. To monitor the ground deformation due to coal mining, a modified time-series InSAR technique combining persistent scatterers (PSs) and distributed scatterers (DSs) is presented in this paper. In particular, DSs are efficiently identified using classified information and statistical characteristics. Furthermore, a two-scale network is introduced into traditional PSI to deal with PSs and DSs in a multi-layer framework by taking the advantage of the robust of PSs and the widely distribution of DSs. The proposed method is performed to investigate the subsidence of Huainan City, Anhui province (China), during 2012–2013 using 14 scenes of Radarsat-2 images. Experimental results show that the proposed method can ease the estimation complexity and significantly increase the spatial density of measurement points, which can provide more detailed deformation information. Result shows that there are obvious subsidence areas detected in the test site with subsidence velocity larger than 5 cm/year. The proposed method brings practical applications for non-urban area deformation monitoring.     

干涉雷达永久散射体自动探测--算法与实验结果

基于理论与模拟实验分析,提出并实现“双重阈值”PS自动探测算法,即时序相关系数阈值法和振幅离差指数阈值法相结合,达到PS自动探测时间效率与可靠性的统一。选用覆盖上海地区的26幅ERS-1/2 C波段SAR图像(1992~2002年),双重阈值PS探测算法得到了检验,实验结果表明,该方法能够有效地提取可靠的PS目标。     

Mexico City subsidence observed with persistent scatterer InSAR

We analyzed 23 satellite SAR (synthetic aperture radar) scenes using Persistent Scatter Interferometry (PSI) to study subsidence in Mexico City associated with groundwater withdrawal. The data were acquired by the Envisat ASAR system between January 2004 and July 2006. The spatial pattern of subsidence and the maximum subsidence rate (300 mm/year) are similar to earlier studies. Comparison to independent GPS data indicates RMS agreement between the two techniques of 6.9 mm/year, about the level expected based on joint data uncertainty. Significant annual variation in the GPS vertical data is not observed, suggesting minimal aquifer recharge during the rainy season, and justifying a simple linear model of phase variation through time for the PSI analysis.     

Hybrid conventional and Persistent Scatterer SAR interferometry for land subsidence monitoring in the Tehran Basin,Iran

Excessive groundwater extraction has caused land subsidence in a large rural area located southwest of Tehran, Iran. We used radar images to estimate the temporal and spatial variation in the magnitude of the subsidence. Due to the large perpendicular baselines and rapid temporal decorrelation of the available data, the application of conventional synthetic aperture radar interferometry (InSAR) to monitor the deformation was not possible. Instead, we applied a recently developed Persistent Scatterer InSAR (PSI) method but found that displacements were underestimated in some areas due to high deformation rates that cause temporal aliasing of the signal. We therefore developed a method that combines conventional InSAR and PSI to estimate the high deformation rates in the southwestern Tehran Basin. We used rates estimated from conventional small temporal baseline interferograms to reduce the likelihood of aliasing and then applied PSI to the residual phase. The method was applied to descending and ascending ENVISAT ASAR images spanning from 2003 to 2009. Mean line-of-sight velocities obtained from both orientations that were further decomposed into horizontal and vertical deformation components were highly compatible with each other, indicating the high performance of the applied method. The mean precision of the estimated vertical component is 2.5 mm/yr. We validated our results using measurements from a continuous GPS station located in one of the subsiding areas. The results also compare favourably with levelling data acquired over a different time interval. Finally, we compared the estimated displacements to hydraulic head variations and geologic profiles at several piezometric wells. We found that the geology is the most important factor controlling the subsidence rate in the southwestern Tehran Basin, regardless of the water level decline.