Analysis of multi-frequency and multi-polarization SAR data for wetland mapping in Hamoun-e-Hirmand wetland

ABSTRACT

The complex, dynamic and narrow boundaries between vegetation types make wetland mapping challenging. Hereafter the case study of the Hamoun-e-Hirmand wetland is considered by analysing eight Synthetic Aperture Radar (SAR) Images acquired in dry and wet periods with three wavelengths (X-band ~ 3 cm, C-band ~ 6 cm, and L-band ~ 25 cm), three polarizations (HH, VV and VH), and four incidence angles (22°, 30°, 34° and 53°). Then, the Support Vector Machine (SVM) classification method was applied to classify TerraSAR-X, Sentinel-1, and ALOS-PALSAR images. The final wetland land cover map was created by combining the classification results obtained from each sensor. In the case in question, results show that TerraSAR-X (X-band, HH-53°) and Sentinel-1 data (C-band, VV-34°) were useful for determining the flooded vegetation area in the wet period. This is crucial for the conservation of water bird habitats since flooded vegetation is an ideal environment for the nesting and feeding of water birds. PALSAR data (L-band in both HH and VH polarizations, 30°) were capable of separating the classes of vegetation density in the wetland. In the dry period, Sentinel-1 (VV and VH, 34°) and TerraSAR-X (HH, 22° and 53°) had higher potential in land cover mapping than PALSAR (HH and VH, 30°). Based on these results, Sentinel-1 in VV and VH provides the highest ability to discriminate between dry and green plants. TerraSAR-X is better for separating meadow and bare land. The results obtained in this paper can reduce the ambiguity in selecting satellite data for wetland studies. The results can also be used to produce more accurate data from satellite images and to facilitate wetland investigation, conservation and restoration.     

Combining differential SAR interferometry and the probability integral method for three-dimensional deformation monitoring of mining areas

With the exploitation of coal resources, ground surface subsidence continues to occur in mining areas, destroying the ecological environment and significantly affecting the daily productivity and life of humans. The differential synthetic aperture radar interferometry (D-InSAR) technique is widely used to monitor ground surface deformation because of its unique advantages such as high accuracy and wide coverage. However, conventional D-InSAR technology provides only one-dimensional (1D) displacement monitoring along the radar line of sight (LOS). This article proposes a method based on an analysis of the mining subsidence law for true three-dimensional (3D) displacement monitoring by combining D-InSAR and a subsidence prediction model based on the probability integral method. In this approach, 1D displacement, obtained using D-InSAR, is then combined with the prediction model to obtain the 3D displacement of ground surface target points. Here, 3D displacement curves were obtained for the Fengfeng mining area (China) using RadarSat-2 images obtained on 9 January and 2 February 2011. True ground surface displacement was measured simultaneously by levelling when the 152under31 s working face was being exploited in Jiulong mine. Vertical displacement and inclined deformation calculated using the proposed method were compared with levelling survey data and the results showed average differences of 3.2 mm and 0.1 mm m^?1, respectively; the calculated maximum displacement in the east–west and south–north directions were 106 and 73 mm, respectively. The spatial distribution of the displacements was in accordance with the mining subsidence law. Thus, the new method can retrieve highly accurate 3D displacements caused by mining subsidence.     

基于时序像素跟踪算法的南伊内里切克冰川运动提取与特征分析

选用Sentinel-1A卫星TOPS模式下获取的8景升轨SAR数据，基于小基线集像素跟踪时序分析技术（Small BAseline Subset Pixel Tracking technique， SBAS-PT），获取了南伊内里切克冰川2018年1月至2018年12月期间不同时段的表面流速分布及其时空变化特征。研究结果表明：2018年南伊内里切克冰川1月到3月整体运动速率较小，从4月起速率明显增加，7月到8月达到最高，9月份起运动速率开始放缓，10月到12月期间冰川表面运动速率较小，全年的平均表面流速约为30cm·d^-1。总体而言，南伊内里切克冰川中上游区域流速明显高于冰川下游，冰川下游冰川物质消融减薄和补给量减少以及表碛物增多等因素致使冰川末端区域逐渐趋于稳定。     

面向地面沉降InSAR干涉图加权叠加方法

针对传统的单幅主影像生成的相干图在干涉叠加过程中相干性低的问题,文章提出了一种基于多幅主影像的合成孔径雷达差分干涉测量(differential interferometric synthetic aperture radar,D-InSAR)加权叠加的方法.该方法利用较少的合成孔径雷达(synthetic apert...     

SAR interferometry in post-seismic ground deformation detection related to the 2001 Bhuj earthquake,India

The 2001 Bhuj earthquake, which occurred due to rupturing of a hidden reverse fault, caused large-scale ground deformation. The ground deformations in the Bhuj earthquake-affected region have been analysed using two interferometric synthetic aperture radar (InSAR) data sets. The data sets belong to the years 2003–2004 and 2004–2005, covering an area east of Bhuj falling on near-flat terrain north of Kutch Mainland Fault (KMF). Two interferograms have been generated successfully displaying the interference fringes in the study area, enabling us to draw interesting observational inferences. The 2003–2004 interferogram image exhibits upliftment of about 8 cm (surface motion towards the satellite) around Kunjisar village and also upliftment of 25 and 5 cm in the other two areas north of Kunjisar, whereas the interferogram image belonging to the year 2004–2005 reveals subsidence of about 17 cm (surface motion away from the satellite) in Kunjisar area along with subsidence of about 28 and 5 cm in the two areas north and northwest of Kunjisar, respectively. Hence, between the years 2003 and 2005, two different episodes of upliftment and subsidence have been observed in the study area. The ground upliftment during 2003–2004 probably indicates that the last phase of ground deformation in the earthquake-affected region has been followed by the onset of subsidence during 2004–2005 as the rock volume involved in stress–strain processes began to experience a relaxation phase.     

Estimation of land subsidence in deltaic areas through differential SAR interferometry: the Po River Delta case study (Northeast Italy)

ABSTRACT

River deltas are very complex environments vulnerable to flooding. Most of the world’s deltas are facing the immediate threat of land subsidence that jeopardizes the safety of millions of people worldwide. In Italy, the Po River Delta (PRD) (Northeast Italy) is an area historically affected by high rate of subsidence due to natural and anthropic factors. Even if the subsidence rates remarkably reduced during the last three decades, this process continues to be alarming in particular in low-lying sectors and along the coastline, where the loss of elevation, combined with the sea-level rise, increases the risk related to flooding. In this study, we monitored the subsidence affecting the entire PRD area with advanced differential interferometric synthetic aperture radar (A-DInSAR) techniques applied to three C-band SAR data sets acquired by the European Remote Sensing satellites, Environmental Satellite, and Sentinel-1A satellite in the last 25 years (from 1992 to 2017). The results of the interferometric processing, consisting of both mean velocity and displacement time series along the satellite line of sight, validated by comparison with levelling and global positioning system measurements, show increasing subsidence moving from the inland to the coastline, with maximum deformation velocities, for the most recent data, in the order of ?30 mm year^?1. In particular, many embankments near the coastal area are affected by high values of subsidence, which increase the flooding hazard of the entire deltaic territory. This work shows the importance of adopting A-DInSAR techniques to update the knowledge of the extent and rates of deformation of subsiding areas in low-lying territories such as river deltas. The outputs of such monitoring can be of primary importance for the future protection of the territory and the flooding risk mitigation.     

Advanced InSAR techniques for deformation studies and for simulating the PS-assisted calibration procedure of Sentinel-1 data: case study from Thessaloniki (Greece), based on the Envisat/ASAR archive

Using state-of-the-art InSAR techniques, namely persistent scatterers (PSs) and small baseline subset (SBAS) approaches, this study contributes to open geotechnical questions in the area of Thessaloniki (Greece) from a remote-sensing perspective. It also demonstrates the potential of these techniques for calibration purposes, with reference to the new C-band synthetic aperture radar (SAR) sensor on board the Sentinel-1 mission satellites. By exploiting the historical archive of Envisat/ASAR data, as well as a pair of the first Sentinel-1A SAR images, recent (2004–2010) deformation rates up to 18 mm year^–1 are detected over the study area. These results are then compared to the findings of previous InSAR and geophysical observations, indicating for example, subsidence or tectonic activity. On the other hand, the usefulness of the PS technique is shown over the same region for external SAR calibration purposes. This process simulates the PS-assisted calibration procedure to be applied systematically to Sentinel-1 SAR products.     

Towards automated mapping and monitoring of potentially dangerous glacial lakes in Bhutan Himalaya using Sentinel-1 Synthetic Aperture Radar data

The majority of glacial lakes around the world are located in remote and hardly accessible regions. The use of remote sensing data is therefore of high importance to identify and assess their potential hazards. However, the persistence of cloud cover, particularly in high mountain areas such as the Himalayas, limits the temporal resolution of optical satellite data with which we can monitor potentially dangerous glacial lakes (PDGLs). The ability of Synthetic Aperture Radar (SAR) satellites to collect data, irrespective of weather and at day or night, facilitates monitoring of PDGLs by without compromising temporal resolution. In this study, we present a semi-automated approach, based on a radar signal intensity threshold between water and non-water feature classes followed by post-processing including elevations, slopes, vegetation and size thresholds, to delineate glacial lakes in Sentinel-1 SAR images in Bhutan Himalaya. We show the capability of our method to be used for delineating and monitoring glacial lakes in Bhutan Himalaya by comparing our results to 10 m resolution Sentinel-2 multispectral data, field survey data, meteorological data, and a time series of monthly images from January to December 2016 of two lakes. Sentinel-1 SAR data can, moreover, be used for detecting lake surface area changes and open water area variations, at temporal resolution of six days, providing substantial advantages over optical satellite data to continuously monitor PDGLs.     

基于PS-InSAR的天津地区沉降监测及分析

城市地面沉降监测是保障城市安全建设和健康发展的重要手段之一，而传统的沉降监测方法无法大尺度反映地面形变信息。针对近几年天津地区出现大面积沉降现象，利用Sentinel-1A数据基于永久散射体干涉测量技术开展城区大范围沉降监测研究并分析了地面沉降原因。结果表明：近年来天津地区多处出现地面沉降，严重沉降区集中天津的武清区、北辰区以及郊区乡镇结合区域的王庆坨镇、胜芳镇、左各庄镇、静海镇以及大寺镇,其最大沉降漏斗位于王庆坨镇，沉降速率为-63.2 mm/a。经分析发现天津地面沉降与地下水过度开采、大型工业区的迁移和建设以及活动断裂带地质活动有关。     

基于PS-InSAR的天津地区沉降监测及分析

城市地面沉降监测是保障城市安全建设和健康发展的重要手段之一,而传统的沉降监测方法无法大尺度反映地面形变信息。针对近几年天津地区出现大面积沉降现象,利用Sentinel-1A数据基于永久散射体干涉测量技术开展城区大范围沉降监测研究并分析了地面沉降原因。结果表明：近年来天津地区多处出现地面沉降,严重沉降区集中天津的武清区、北辰区以及郊区乡镇结合区域的王庆坨镇、胜芳镇、左各庄镇、静海镇以及大寺镇,其最大沉降漏斗位于王庆坨镇,沉降速率为-63.2 mm/a。经分析发现天津地面沉降与地下水过度开采、大型工业区的迁移和建设以及活动断裂带地质活动有关。     

多源遥感数据小麦识别及长势监测比较研究

小麦是我国主要的农作物之一,对于我国的经济发展有着重要意义.遥感技术经过不断发展,已成为提取小麦及长势研究的重要手段.利用高光谱珠海一号OHS-2A卫星、多光谱Sentinel-2A卫星以及MODIS等多源遥感数据,以雄安为研究区,采用支持向量机的方法进行小麦提取,结合野外实测数据利用混淆矩阵进行精度评价分析;分别对比...     

基于D-InSAR技术的淮南矿区地面沉陷监测

针对常规的通过大地水准测量、GPS测量监测矿区地面沉陷的技术存在监测周期长、成本高、无法全面监测等缺陷,提出了一种基于D-InSAR技术的矿区地面沉陷监测方法。以淮南矿区为试验区,采用两轨法D-InSAR技术,利用该地区2个时相的ALOS PALSAR数据获取了淮南矿区试验时间段内的地面形变图,分析了淮南矿区各矿的地面沉陷信息。结果表明,煤矿开采区存在5~25 cm不同程度的沉陷,与实际情况相符,因此,基于D-InSAR技术的监测方法可以作为一种获取矿区大范围的地表沉陷信息的有效方法。     

Surface displacement of the Mw 7 Machaze earthquake (Mozambique): Complementary use of multiband InSAR and radar amplitude image correlation with elastic modelling

In this paper we investigate the surface displacement related to the 2006 Machaze earthquake using Synthetic Aperture Radar Interferometry (InSAR) and sub-pixel correlation (SPC) of radar amplitude images. We focus on surface displacement measurement during three stages of the seismic cycle. First, we examined the co-seismic stage, using an Advanced SAR (ASAR) sensor onboard the Envisat satellite. Then we investigated the post-seismic stage using the Phase Array L-band SAR sensor (PALSAR) onboard the ALOS satellite. Lastly, we focussed on the inter-seismic stage, prior to the earthquake by analysing the L-band JERS-1 SAR data. The high degree of signal decorrelation in the C-band co-seismic interferogram hinders a correct positioning of the surface rupture and correct phase unwrapping. The post-seismic L-band interferograms reveal a time-constant surface displacement, causing subsidence of the surface at a ∼ 5 cm/yr rate. This phenomenon continued to affect the close rupture field for at least two years following the earthquake and intrinsically reveals a candidate seismogenic fault trace that we use as a proxy for an inversion against an elastic dislocation model. Prior to the earthquake, the JERS interferograms do not indicate any traces of pre-seismic slip on the seismogenic fault. Therefore, slip after the earthquake is post-seismic, and it was triggered by the Machaze earthquake. This feature represents a prominent post-seismic slip event rarely observed in such a geodynamic context.     

D-InSAR monitoring of crustal deformation in the eastern segment of the Altyn Tagh Fault

In recent years, the differential Interferometric Synthetic Aperture Radar (D-InSAR) technique has been widely used in monitoring deformation on the Earth's surface. Compared with conventional approaches (such as global positioning system (GPS) monitoring), application of the D-InSAR technique has many advantages in surface deformation monitoring. In this paper, the D-InSAR technique is applied to study the crustal deformation characteristics of the eastern segment of the Altyn Tagh Fault (ATF), which is an important boundary of crustal deformation in the north-eastern area of the Tibetan Plateau. To the north of the boundary, the deformation gradually decreases from 2.8 cm in the west to 0.8 cm in the east; to the south of the boundary, the deformation presents different characteristics at the two sides of the western part of the North Qilian Shan Fault (NQF). At the south-west side, the deformation is intense, with relatively weaker deformation of 1.6～2.1 cm inside the Changma Basin and stronger deformation of 2.2～6.0 cm outside the Changma Basin. At the north-east side, the deformation is smaller than that in the other side, with a decrease from 1.3 cm in the west to nearly 0 cm in the east. North-east to the western part of the NQF, there exists negative deformation. This is because when the northern margin of the Tibetan Plateau was moving to the north-east, it was blocked off by the rigid Alashan Block and was bent down close to the north-east of the Qilian Shan Orogen to form a foreland basin. This paper also shows that currently the ATF is active and has left-lateral strike-slip. The slip rate of the eastern segment of the ATF is 4.7 mm/year. For different locations, the slip rate is different.     

利用Sentinel-1A合成孔径雷达干涉时间序列监测陇东地区地面沉降变形

基于覆盖陇东地区同一轨道的97景Sentinel-1A卫星影像,在ISCE和StaMPS数据处理平台上利用PS-InSAR技术进行叠加数据处理,获得研究区自2014年10月至2019年5月的年平均地表LOS向形变场,并对形变场结果进行二维网格滤波处理,获取沉降中心的变化特征。研究结果表明：陇东地区主要存在两类形变,一类是由构造活动引起的地表形变,主要分布在海原断裂与六盘山东麓断裂转换区附近,跨海原断裂年平均形变约为1 mm/a,而六盘山东麓断裂附近断层无明显变形,鄂尔多斯块体内部变形微弱;另一类则是由人类工业活动,如煤矿开采、地下水开采活动等导致的地表沉降,主要影响区域为华亭矿区和宁正矿区,均呈现漏斗状沉降形态,年均最大沉降分别约为8 mm/a和30 mm/a。     

Surface Deformation Field of Eastern Gansu Province by PS-InSAR Technique with Sentinel-1A

Through taking 97 Sentinel-1A SAR images from October 2014 to May 2019 covered most parts of Eastern Gansu province as experimental data, we monitored the surface deformation applying PS-InSAR technique for superimposed data processing based on ISCE and StaMPS to obtain the annual mean LOS rate of surface deformation field. Moreover, we filtered the LOS velocity field using two-dimensional mesh filtering to obtain the variation characteristics of the subsidence center. Our results reveal that there have two patterns of surface deformation. (1) Ground deformation caused by tectonic activity mainly locates around Haiyuan fault, whose mean annual LOS rate of deformation is ~1mm/a. However, there is no obvious deformation near the Liupanshan fault. Meanwhile, the internal deformation of the Ordos Block is subtle. (2) Another surficial deformation caused by mining activity occurs in the regions of Huating Mining Area and Ningzheng Mining Area, in which a ground subsidence funnel has been found. According to the time series deformation characteristic analysis of the settlement center, we know the mean annual LOS rate of deformation in the Huating Mining Area and Ningzheng Mining Area are ~8 mm/a and ~30 mm/a, respectively.     

C波段无线网络通信技术及在飞行试验遥测中应用构想

在分析国内外C波段无线网络通信研究进展基础上,结合现行飞行试验遥测中遇到的技术瓶颈,提出了将C波段无线网络通信技术应用于飞行试验遥测中的构想,建立基于C波段的无线网络的空地一体化遥测网络体系。C波段空地网络化遥测链路的建立,扩展遥测数据传输可用频段的同时增加上行通道,建立机载网络系统与地面监控网络的网络通信链路,为未来空天地一体化遥测网络的建立建立技术基础;同时利用通用的网络管理流程,对整个测试资源动态配比,提高试飞效率。     

Sensitivity of Sentinel-1 backscatter to characteristics of buildings

In this study, Sentinel-1 interferometric wide swath (IW) mode backscatter is analysed with respect to physical parameters of buildings in Tallinn, Estonia. Dependence on height, alignment, density, shape, and material is shown and discussed. Distribution of backscatter was estimated with respect to each of the parameters, and a correlation matrix of all physical parameters and backscatter values was computed. Height has the strongest effect on backscatter values for both polarization bands, while shape and alignment to orbit has weaker effect on the backscatter. Relationship of co-polarized and cross-polarized backscatter with how a building is aligned with respect to the satellite’s look angle indicates that double bounce from wall–ground interactions is still the dominant scattering mechanism detected by Sentinel-1 in IW mode with 20 m resolution. In order to establish possible detection problems related to specifically oriented buildings at different latitudes, dihedral backscatter is modelled for buildings of oblong and square shapes. Results from this study should be used to improve existing and develop new urban area detection methods based on Sentinel-1 data.     

Sentinel-2 Satellite Image Fusion Methodand Quality Evaluation Analysis

Sentinel-2 satellite sensors acquire three kinds of optical remote sensing images with different spatial resolutions.How to improve the spatial resolution of lower spatial resolution bands by fusion method is one of the problems faced by Sentinel-2 applications.Taking the Sentinel\|2B image as the data source,a high spatial resolution band was generated or selected from the four 10m spatial resolution bands by four methods:the maximum correlation coefficient,the central wavelength nearest neighbor,the pixel maximum and the principal component analysis.We fused the one high spatial resolution band produced and six multispectral bands with 20 m spatial resolution by the five fusion methods of PCA,HPF,WT,GS and Pansharp to produce six multispectral bands with 10 m spatial resolution and the fusion results were evaluated from three aspects:qualitative and quantitative (information entropy,average gradient,spectral correlation coefficient,root mean square error and general image quality index) and classification accuracy of fused images.Results show that the fusion quality of Pansharp with the maximum correlation coefficient is better than other fusion methods,and the classification accuracy is slightly lower than the GS with the pixel maximum of the highest classification accuracy and far higher than the original four multispectral image with 10 m spatial resolution.According to the classification accuracy of experimental data,different fusion methods have different advantages in extraction of different ground objects.In application,appropriate schemes should be selected according to actual research needs.This research can provide reference for Sentinel-2 satellite and similar satellite data processing and application.     

D-InSAR技术在煤矿区沉陷监测中的研究

文章介绍了近年来D-InSAR技术在煤矿区沉陷监测的应用和发展,探讨了该技术用于监测煤矿区沉陷的可行性、与传统的变形监测技术对比所具有的优势,并指出了目前该技术在煤矿区沉陷监测中存在的问题及解决方法。