DEM error retrieval by analyzing time series of differential interferograms

International audience2-pass Differential Synthetic Aperture Radar Interferometry (D-InSAR) processing have been successfully used by the scientific community to derive velocity fields. Nevertheless, a precise Digital Elevation Model (DEM) is necessary to remove the topographic component from the interferograms. This letter presents a novel method to detect and retrieve DEM errors by analyzing time series of differential interferograms. The principle of the method is based on the comparison of fringe patterns with the perpendicular baseline. First, a mathematical description of the algorithm is exposed. Then, the algorithm is applied on a series of four one-day ERS-1/2 interferograms

Radar-Coding and Geocoding Lookup Tables for the Fusion of GIS Data and SAR images in Mountain Areas

International audienceSynthetic aperture radar (SAR) image orthorectification induces an important alteration of information due to the side-looking geometry of SAR acquisition. In high-relief areas, the difficulty is increased by the foldover effect: The images acquired with low incidence angles cannot be registered by a bijective transformation like polynomial transformations, as usually proposed by conventional software. In this letter, a simple and efficient method, fitted to geocoded data and SAR images, is introduced to propose a generic coregistration tool that takes SAR geometry into account without requiring the exact sensor model, specific parameters, and precise navigation data. This method is based on a simulated SAR image and on the computation of lookup tables (LUTs) that represent the coordinate transform from one geometry to the other. Results are presented on a high-relief area in the Alps, where satellite and airborne SAR images are used for glacier evolution monitoring. A comparison to other sensor-independent approaches has been performed, showing that the proposed approach performs better in mountain areas. The resulting LUTs allow merging SAR data with the georeferenced data, either in ground geometry by orthorectifying the SAR information or in radar geometry by the inverse transformation, namely, radar-coding data from a geographic information system, to improve the analysis of SAR images and the result interpretation

The RESEARCH project. Soil-related hazards and archaeological heritage in the challenge of climate change

Archaeological Heritage, naturally endangered by environmental processes and anthropogenic pressures, is today increasingly at risk, because of intense human activities and climate change, and their impact on atmosphere and soil. European research is increasingly dedicated to the development of good practices for monitoring archaeological sites and their preservation. One of the running projects about these topics is RESEARCH (Remote Sensing techniques for Archaeology; H2020-MSCA-RISE, grant agreement: 823987), started in 2018 and ending in 2022. RESEARCH aims at testing risk assessment methodology using an integrated system of documentation and research in the fields of archaeology and environmental studies. It will introduce a strategy and select the most efficient tools for the harmonization of different data, criteria, and indicators in order to produce an effective risk assessment. These will be used to assess and monitor the impact of soil erosion, land movement, and land-use change on tangible archaeological heritage assets. As a final product, the Project addresses the development of a multi-task thematic platform, combining advanced remote sensing technologies with GIS application. The demonstration and validation of the Platform will be conducted on six case studies located in Italy, Greece, Cyprus, and Poland, and variously affected by the threats considered by the Project. In the frame of RISE (Research and Innovation Staff Exchange), RESEARCH will coordinate the existing expertise and research efforts of seven beneficiaries into a synergetic plan of collaborations and exchanges of personnel (Ph.D. students and research staff), to offer a comprehensive transfer of knowledge and training environment for the researchers in the specific area. This paper aims at illustrating the results of the activities conducted during the first year of the Project, which consisted in developing an effective risk assessment methodology for soil-related threats affecting archaeological heritage, and defining the scientific requirements and the user requirements of the Platform. The activities have been conducted in synergy with all the Partners and were supported by the possibility of staff exchange allowed by the funding frame MSCA-RISE

Co-seismic ground deformation of Yushu Earthquake detected with D-InSAR technique

An earthquake of magnitude 7.1 suddenly occurred in Yushu county of Qinghai province on April 14, 2010. This paper presents the studies of using the data of Advanced Land Observing Satellite-Phased Array type L-band Synthetic Aperture Radar (ALOS-PALSAR) before and after the earthquake to examine and calculate the co-seismic ground deformation. The differential SAR interferometry (D-InSAR) technique is used. The results show that the earthquake caused the ground deformation over a large area. The extension of the ground deformation followed the south-east to east direction and along the Yushu-Ganzi fault zone. The largest deformation was found about 350 mm at 33.7°N 96.81°E. It is along the line of sight (LOS) of SAR and can be detected with D-InSAR technique. The detected ground deformation was mainly uplifting. The detected ground deformation has an important value for evaluating the extent of ground damage and seismicity in Yushu after earthquake, inferring the nature of the quake faulting, and studying characteristics of seismic deformation. 2010-04-14青海玉树发生7.1级地震后, 作者利用震前和震后获取的日本ALOS卫星PALSAR遥感数据, 开展了差分干涉雷达(D-InSAR)地震同震形变测量与分析。结果表明: 玉树地震引起较大范围地表变形, 地震变形沿玉树—甘孜断裂带向南东东方向扩展, 在N33.7°, E96.81°附近达到最大形变量, D-InSAR监测到雷达视向上的最大形变量为35cm。地表形变特征对于评价玉树地震破坏程度、推断断层性质、研究地震形变和地震孕育特征具有重要的参考价值

DEFORMATION MONITORING IN AND AROUND THE NATIONAL CAPITAL REGION OF INDIA USING DINSAR TECHNIQUE

Urbanization increases the pressure on land and ground water. Due to pressure on land and over extraction of the ground water for modernization and development, deformation of land increase. The traditional deformation monitoring techniques are costly and time taking. The Differential Interferometry Technique (DInSAR) has capability to monitor regional scale deformation. Recently Vasundra region of the NCR has experienced a road subsidence near to the multiple stories building. In the study we have attempted to identify the Vasundra and nearby region by the DInSAR technology to identify the deformation in Delhi and NCR focused on the Vasundra area of Ghaziabad, Uttar Pradesh, India. This is one of the developed and planned area in the Ghaziabad District. The Sentinel-1 C data has been used to monitor the deformation in that area. The Vasundra area has been deformed due to heavy rainfall and water logging in the surrounding area by which the road has been subsided up to 30 feet. Using the sentinel data we were able to identify the subsidence in Vasundra and nearby areas. Since the Sentinel scene was very big so a clear picture of the deformation indication in the NCR region are found which need more in-depth study further. Conclusively it can be said that DInSAR technique with Microwave data is a competent tool to monitor the minute deformation

Analysing landslides in the Three Gorges Region (China) using frequently acquired SAR images

Spaceborne Synthetic Aperture Radar (SAR) sensors obtain regular and frequent radar images from which ground motion can be precisely detected using a variety of different techniques. The ability to remotely measure slope displacements over large regions has many uses and advantages, although the limitations of an increasingly common technique, Differential SAR Interferometry (D-InSAR), must be considered to avoid the misinterpretation of results. Areas of low coherence and the geometrical effects of mountainous terrain in SAR imagery are known to hinder the exploitation of D-InSAR results. A further major limitation for landslide studies is the assumption that variable rates of movement over a given distance cannot exceed a threshold value, dependent upon the SAR image pixel spacing, the radar sensor wavelength and satellite revisit frequency. This study evaluates the use of three SAR image modes from TerraSAR-X and ENVISAT satellites for monitoring slow-moving landslides in the densely vegetated Three Gorges region, China. Low coherence and episodically fast movements are shown to exceed the measureable limit for regular D-InSAR analysis even for the highest resolution, 11-day interferograms. Subsequently, sub-pixel offset time-series techniques applied to corner reflectors and natural targets are developed as a robust method of resolving time-variable displacements. Verifiable offsets are generated with the TerraSAR-X imagery and the precise movement history of landslides is obtained over a period of up to four years. The capability to derive two-dimensional movements from sub-pixel offsets is used to infer a rotational failure mechanism for the most active landslide detected, and a greater understanding of the landslide behaviour is achieved through comparisons with likely triggering factors and 2D limit equilibrium slope stability analysis

Managing the natural disasters from space technology inputs

Natural disasters, whether of meteorological origin such as Cyclones, Floods, Tornadoes and Droughts or of having geological nature such as earthquakes and volcanoes, are well known for their devastating impacts on human life, economy and environment. With tropical climate and unstable land forms, coupled with high population density, poverty, illiteracy and lack of infrastructure development, developing countries are more vulnerable to suffer from the damaging potential of such disasters. Though it is almost impossible to completely neutralise the damage due to these disasters, it is, however possible to (i) minimise the potential risks by developing disaster early warning strategies (ii) prepare developmental plans to provide resilience to such disasters, (iii) mobilize resources including communication and telemedicinal services and (iv) to help in rehabilitation and post-disaster reconstruction. Space borne platforms have demonstrated their capability in efficient disaster management. While communication satellites help in disaster warning, relief mobilisation and telemedicinal support, Earth observation satellites provide the basic support in pre-disaster preparedness programmes, in-disaster response and monitoring activities, and post-disaster reconstruction. The paper examines the information requirements for disaster risk management, assess developing country capabilities for building the necessary decision support systems, and evaluate the role of satellite remote sensing. It describes several examples of initiatives from developing countries in their attempt to evolve a suitable strategy for disaster preparedness and operational framework for the disaster management Using remote sensing data in conjunction with other collateral information. It concludes with suggestions and recommendations to establish a worldwide network of necessary space and ground segments towards strengthening the technological capabilities for disaster management and mitigation